KVL is based on the assumption that there is no fluctuating magnetic field linking the closed loop. This is not a safe assumption for high-frequency (short-wavelength) AC circuits.[2] In the presence of a changing magnetic field the electric field is not a conservative vector field. Therefore, the electric field cannot be the gradient of any potential. That is to say, the line integral of the electric field around the loop is not zero, directly contradicting KVL.But then Electrobooms arguments are convincing too.
It is often possible to improve the applicability of KVL by considering "parasitic inductances" (including mutual inductances) distributed along the conductors.[2] These are treated as imaginary circuit elements that produce a voltage drop equal to the rate-of-change of the flux.
From WikipediaQuoteIt is often possible to improve the applicability of KVL by considering "parasitic inductances" (including mutual inductances) distributed along the conductors.
Thanks HackedFridgeMagnet, "KVL is based on the assumption that there is no fluctuating magnetic field linking the closed loop" which is true and KVL only holds up for a static field. However, if you take into account all of the parasitic and stray circuit elements then KVL still holds up if you have a vaying magnetic field, however, you've got a different circuit than what you started with. Both Lewin and Electroboom are right, all depends on whether you model in the parasitics. KVL still holds for varying magnetic field if and only if you model in the parasitic circuit elements
KVL is based on the assumption that there is no fluctuating magnetic field linking the closed loop. This is not a safe assumption for high-frequency (short-wavelength) AC circuits.[2] In the presence of a changing magnetic field the electric field is not a conservative vector field. Therefore, the electric field cannot be the gradient of any potential. That is to say, the line integral of the electric field around the loop is not zero, directly contradicting KVL.
It is often possible to improve the applicability of KVL by considering "parasitic inductances" (including mutual inductances) distributed along the conductors.[2] These are treated as imaginary circuit elements that produce a voltage drop equal to the rate-of-change of the flux.
Maybe the demonstration by Walter Lewin doesn't really show what he is trying to show?
I would also say that both are right in a certain way.I agree. Especially with the last part. This has been discussed before and it seems Dr. Lewin is just trolling.
Kirchoffs law doesn't hold in a magnetic field if you don't model the effect of the field on the inductance. But does work if you model the parasitics of the wire as instructors.
This is an excellent paradox to get people thinking. But Dr. Lewin should explain that the problem is a bad circuit model ignoring what should not be ignored rather than the ever so useful Kirchhoffs law being wrong.
I would also say that both are right in a certain way.I agree. Especially with the last part. This has been discussed before and it seems Dr. Lewin is just trolling.
Kirchoffs law doesn't hold in a magnetic field if you don't model the effect of the field on the inductance. But does work if you model the parasitics of the wire as instructors.
This is an excellent paradox to get people thinking. But Dr. Lewin should explain that the problem is a bad circuit model ignoring what should not be ignored rather than the ever so useful Kirchhoffs law being wrong.
That said, even if we consider a perfect setup and a real discrepancy, my take here would be that KVL could still perfectly apply. We would just have to consider the loop having extra voltage sources from any induced voltage. That wouldn't defeat it, but make us consider that our circuit model is incomplete.
That said, even if we consider a perfect setup and a real discrepancy, my take here would be that KVL could still perfectly apply. We would just have to consider the loop having extra voltage sources from any induced voltage. That wouldn't defeat it, but make us consider that our circuit model is incomplete.
Simply put:
You don't get to pick and choose when you follow a law and when you don't.
This is physics, not politics~~
Tim
Not sure I got your point, nor that you got mine.
I've yet to agree with KVL not being met, until I get a consistent and formal proof of that.
Any electrical circuit made of physical, non-ideal components and non-zero length, non-zero impedance connections between them will get inductive and capacitive coupling with its surroundings. If you devise the real, physical circuit that it actually is...
physics is a domain where this is strictly prohibited. :)
I have a hard time believing that Lewin is "just trolling" or trying to get students to think as some have suggested, after reading his responses to Mehdi and others on his original video. I think this link will work, if not just look for ElectroBOOM's comment on the video, it should be near the top: https://goo.gl/JsKHb8.
If Lewin has a more subtle point he's trying to make, he's doing a good job of hiding it.
In electric engineering terms we say, it DOES matter how I twist or coil the leads of my voltmeter.
He'll do a video when he gets back from vacation in a week :popcorn:Thanks for you polite request on our behalf.
(https://i.imgur.com/6bDVfdr.png)
In electric engineering terms we say, it DOES matter how I twist or coil the leads of my voltmeter.
In the real world it can (and in this case demonstrably does) matter how you twist or coil the leads. There is transformer coupling happening which is not shown on your theoretical circuit.
He'll do a video when he gets back from vacation in a week :popcorn:There may be moderation. I see the prof’s answer in the thread, but not your comment.
(https://i.imgur.com/6bDVfdr.png)
As a relevant point of interest, you cannot have a half-turn transformer winding. It is always an integer number of turns. You have to connect the ends of your 'half turn' winding together somehow, for current to flow. Making the wire longer, as in including the test leads of a meter for example, does not alter the fact that the circuit still completes the same magnetic path as a complete turn would do. The longer wire intercepts a more diffuse magnetic field but over a longer distance, and the induced EMF is the same as if it were a tightly wound turn.Fractional turns can be done. http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.187.2764&rep=rep1&type=pdf (http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.187.2764&rep=rep1&type=pdf)
In the case of an induced emf the potentials in a circuit are no longer determined, they depend on the path and thus Kirchhoff's Loop Rule is not valid. Kirchhoff's Loop Rule is a special case of Faraday's Law (namely when phi/dt=0). Thus Faraday's Law is always valid.
For case 2 we say "in a variable field a voltage is induced in the voltmeter's leads", or "the leads act as voltage sources, too", or whatever, which is nothing more than (a wrong way of) saying that "the path DOES matter when moving charges in a variable (non-conservative) field".
If this were intentionally done to make his students think about the problem, his video would congratulate the student who figures out the omission/trick of how he produced this result
He even takes this argument so far to the point of saying that Kirchoff's voltage law does not apply to circuits with inductors, because they have a changing magnetic field:
http://web.mit.edu/8.02/www/Spring02/lectures/lecsup4-1.pdf (http://web.mit.edu/8.02/www/Spring02/lectures/lecsup4-1.pdf)
If you want to play this "path" game, and insist that voltage is not by default the lowest energy path between the two points, then you have to say that the voltage between those point is undefinable, no?
He even takes this argument so far to the point of saying that Kirchoff's voltage law does not apply to circuits with inductors, because they have a changing magnetic field:
http://web.mit.edu/8.02/www/Spring02/lectures/lecsup4-1.pdf (http://web.mit.edu/8.02/www/Spring02/lectures/lecsup4-1.pdf)
Thanks for the reference. This helps making it much clearer what he was meaning - especially on page 3.
He even takes this argument so far to the point of saying that Kirchoff's voltage law does not apply to circuits with inductors, because they have a changing magnetic field:
http://web.mit.edu/8.02/www/Spring02/lectures/lecsup4-1.pdf (http://web.mit.edu/8.02/www/Spring02/lectures/lecsup4-1.pdf)
Suppose you put the probes of a voltmeter across the terminals of an inductor (with very small resistance) in a circuit. What will you measure? What you will measure on the meter of the voltmeter is a "voltage drop" of Ldi/dt. But that is not because there is an electric field in the inductor! It is because putting the voltmeter in the circuit will result in a time changing magnetic flux through the voltmeter circuit, consisting of the inductor, the voltmeter leads, and the large internal resistor in the voltmeter
a case of theoretical physics vs practical engineering approaches.
The meter wires are part of the circuit and the orientation of the wires determines the results.
He even takes this argument so far to the point of saying that Kirchoff's voltage law does not apply to circuits with inductors, because they have a changing magnetic field:
http://web.mit.edu/8.02/www/Spring02/lectures/lecsup4-1.pdf (http://web.mit.edu/8.02/www/Spring02/lectures/lecsup4-1.pdf)
Thanks for the reference. This helps making it much clearer what he was meaning - especially on page 3.
We've discussed this many times in previous threads. Dr. Lewin gave his world famous SUPER DEMO as he refers to it in 2002, I guess. But he didn't invent it. It is an exact recreation of the experiment in this 1982 paper:
http://www.phy.pmf.unizg.hr/~npoljak/files/clanci/guias.pdf (http://www.phy.pmf.unizg.hr/~npoljak/files/clanci/guias.pdf)
In the paper, everything is explained very simply without drama. It's no mystery. The meter wires are part of the circuit and the orientation of the wires determines the results.
The meter wires are part of the circuit and the orientation of the wires determines the results.
What happens if we remove the voltmeters? How do we measure the voltage without the voltmeters? We will need to take an electric charge and drag it through the circuit from A to B. How much energy do we need to move our charge from A to B?
The answer is: it depends. If we go from A to B through the left side, or through the right side. Not only that the energy is different for each half of the circuit, but it has an opposite sign. No chance to get a zero for the whole loop.
As a relevant point of interest, you cannot have a half-turn transformer winding.
http://www.phy.pmf.unizg.hr/~npoljak/files/clanci/guias.pdf (http://www.phy.pmf.unizg.hr/~npoljak/files/clanci/guias.pdf)
Question:
If we remove the voltmeters and their leads, what is the voltage between A and B?
An even simpler question:
No voltmeters, no leads, no wires. Is the voltage between A and B positive, or negative? <- drama, it's both! :o
It is not like he taught advanced physics. From what I've seen his lectures were more like physically themed perfo rmances rather than actual lectures. This was fine for the first year EEs that have never seen physics before.
What happens if we remove the voltmeters? How do we measure the voltage without the voltmeters? We will need to take an electric charge and drag it through the circuit from A to B. How much energy do we need to move our charge from A to B?
The answer is: it depends. If we go from A to B through the left side, or through the right side. Not only that the energy is different for each half of the circuit, but it has an opposite sign. No chance to get a zero for the whole loop.
We've discussed this many times in previous threads. Dr. Lewin gave his world famous SUPER DEMO as he refers to it in 2002, I guess. But he didn't invent it. It is an exact recreation of the experiment in this 1982 paper:
http://www.phy.pmf.unizg.hr/~npoljak/files/clanci/guias.pdf (http://www.phy.pmf.unizg.hr/~npoljak/files/clanci/guias.pdf)
In the paper, everything is explained very simply without drama. It's no mystery. The meter wires are part of the circuit and the orientation of the wires determines the results.
QuoteWhat happens if we remove the voltmeters? How do we measure the voltage without the voltmeters? We will need to take an electric charge and drag it through the circuit from A to B. How much energy do we need to move our charge from A to B?
The answer is: it depends. If we go from A to B through the left side, or through the right side. Not only that the energy is different for each half of the circuit, but it has an opposite sign. No chance to get a zero for the whole loop.
Well, when measuring voltage, why are we "dragging the electron" where it doesn't want to go? Isn't the usual way to do this to let the electron go where it wants? If you have to drag it one way and input energy, and the opposite is true for the other direction, it will take the other way every time. This is why the electrons go in a circle, here, right? From A to B via route 1, and B to A via route 2?
so hmm. it this a close analogy?
A mobius strip doesn't have a front and a back.... So therefore all the dummies using the term front and back are really talking about a special case (which is pretty much everything except a contrived thought experiment). So it is therefore an OUTRAGE for textbooks to be incorrectly stating that things have fronts and backs when it is not universally the case?
[Kirchhoff's Voltages Law (KVL) failure] would be sorta like doing a momentum analysis between two colliding steel balls without figuring the effect of a magnet under the table.:-+
Before taking his degree, Kirchhoff had begun his work in original
research, and published a remarkable paper on electrical conduction in
a thin plate, especially a circular one. His problem was to find the
current in any branch of a network of linear conductors. Starting
from Ohm's familiar law, he derived two results long recognized in
electrical science as Kirchhoff 's laws.
Come to re-think of it, and as he's clearly not an idiot, I was then willing to believe that he actually did that on purpose, just to make young students aware of the question: using simplistic models while thinking they hold true in the real world, which is a very common pitfall. This would be all good if he made it clear in the end that it was his intent instead of making it even more confusing, to the point that he even managed to confuse some very experienced engineers, using his position of authority.Precisely.
Now if he was genuinely trying to instill advanced physics notions in young heads, I think this was a very bad way of doing it from a pedagogical standpoint.
I'll say the professor was correct when he said we can not always apply KVL. Of course, if we first transform the real circuit into a lumped circuit, where we add the externally induced voltages as voltage sources internal to our circuit, then we obtain a new circuit that obeys KVL.
I'll say the professor was correct when he said we can not always apply KVL. Of course, if we first transform the real circuit into a lumped circuit, where we add the externally induced voltages as voltage sources internal to our circuit, then we obtain a new circuit that obeys KVL.
Wow. I was not even aware that there is such a controversy over Kirchhoff's law.
I though Kirchhoff's laws were derivable from Faraday's law and Maxwell equations in general. But quick search shows that it is not very easy.
Dr. Lewin's response to this is: You can't do that! You can't just move the EMF from one side of the equation to the other! That's dead wrong! That's criminal. (https://bit.ly/2qzwkh0 (https://bit.ly/2qzwkh0))
You can't do that with changing magnetic fields. Curl-E = -dB/dt, so there is no scalar potential that describes electron motion. That is what Walter Lewin was showing. Everything else is just noise.
... is a very big claim that two points on the same circuit measure differently... This is why many people have a big problem with this.
However, there are no such inductors or capacitors. If we consider their existence, they must be infinitesimal. There are infinite infinitely tiny inductors and capacitors, and for Kirchhoff to hold you will have to apply it to infinite meshes.
This is just a simple example, but we can see that Kirchhoff is not adequate to model situations like that.
For a finite number of lumped components where space and time can be disconsidered, Kirchhoff is fine.
But add space and time and you'd be better off with a theory that takes that into consideration, and that is Faraday-Maxwell.
However, there are no such inductors or capacitors. If we consider their existence, they must be infinitesimal. There are infinite infinitely tiny inductors and capacitors, and for Kirchhoff to hold you will have to apply it to infinite meshes.
This is just a simple example, but we can see that Kirchhoff is not adequate to model situations like that.
For a finite number of lumped components where space and time can be disconsidered, Kirchhoff is fine.
But add space and time and you'd be better off with a theory that takes that into consideration, and that is Faraday-Maxwell.
Say the EMF induced in the loop is 1V. Say the total resistance is 1 ohm, so you have 1 amp flowing around the loop. Take any point in the loop and go around the loop adding up the IR drop. Go all the way around the loop. You always end up with 1V, not zero.No in this case you will end up with 0v if you measure it.
So how are you going to model this to make Kirchoff's law work? An infinite number of resistors dR and an infinite number of voltage sources dV? (I don't think so.)
Say the EMF induced in the loop is 1V. Say the total resistance is 1 ohm, so you have 1 amp flowing around the loop. Take any point in the loop and go around the loop adding up the IR drop. Go all the way around the loop. You always end up with 1V, not zero.No in this case you will end up with 0v if you measure it.
So how are you going to model this to make Kirchoff's law work? An infinite number of resistors dR and an infinite number of voltage sources dV? (I don't think so.)
You're misinterpreting Faraday-Maxwell.
I am fairly sure Maxwell-Faraday describes a case where the loop is magnetically closed but electrically open circuit.I'm fairly sure you are misinterpreting it.
But maybe I wasn't clear. Say you have the resistive loop. If you could measure say a section 1/10th of the way around. (I admit it is not easy to accurately measure in the presence of the magnetic field.) So that section has resistance 1/10th of an ohm and has current 1A flowing. You should measure 0.1V. So there are 10 pieces, and if you add them up, you get 1V, not 0V. You could divide it up in other numbers of sections with the same result.In your example you are measuring just one section of the loop. In the thought experiment, you are measuring the voltage across two points which are connected by two half loops of wire.
OK, well take the original demo, but instead of two resistors, make the whole loop one big resistor. That is, a loop made out of resistive material:
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=569548;image)
Say the EMF induced in the loop is 1V. Say the total resistance is 1 ohm, so you have 1 amp flowing around the loop. Take any point in the loop and go around the loop adding up the IR drop. Go all the way around the loop. You always end up with 1V, not zero.
So how are you going to model this to make Kirchoff's law work? An infinite number of resistors dR and an infinite number of voltage sources dV? (I don't think so.)
OK, well take the original demo, but instead of two resistors, make the whole loop one big resistor. That is, a loop made out of resistive material:
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=569548;image)
Say the EMF induced in the loop is 1V. Say the total resistance is 1 ohm, so you have 1 amp flowing around the loop. Take any point in the loop and go around the loop adding up the IR drop. Go all the way around the loop. You always end up with 1V, not zero.
So how are you going to model this to make Kirchoff's law work? An infinite number of resistors dR and an infinite number of voltage sources dV? (I don't think so.)
Interestingly yes you would get zero volts in this case!
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=569761;image)
It turns out you can poke any two points in this circle and have the points sit at 0V...
1) Voltage1 = Potential in point A - Potential in point B
2) Voltage2 = The energy required to move a unit of charge between A and B
It turns out you can poke any two points in this circle and have the points sit at 0V...
That is wrong. Your model is wrong. It led you to the wrong conclusion.
Do you find following model as matching your "whole loop one big 1 Ohm resistor" ?
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=570035;image)
But what happens if we instead remove the restive ring but leave the probe wires connecting to the same two points in space connected to nothing? Do we measure nothing?
No, that still would have each voltage source + resistor pair cancelling out to 0V.
I'm not sure how to make a model with lumped components that violates KVL.
QuoteI'm not sure how to make a model with lumped components that violates KVL.
LOL. You basically said: "you are wrong, but I cannot prove it" :-DD
Using Faraday's law on the resistive loop, integrating E dot dl around the loop doesn't equal zero.
KVL holds for lumped circuits. This isn't a lumped circuit.
So to dispprove KVL within Time varying magnetic fields I suggest you need to prove it in the lab.
IMO I don't think Dr Lewin did this.
We've discussed this many times in previous threads. Dr. Lewin gave his world famous SUPER DEMO as he refers to it in 2002, I guess. But he didn't invent it. It is an exact recreation of the experiment in this 1982 paper:
http://www.phy.pmf.unizg.hr/~npoljak/files/clanci/guias.pdf (http://www.phy.pmf.unizg.hr/~npoljak/files/clanci/guias.pdf)
In the paper, everything is explained very simply without drama. It's no mystery. The meter wires are part of the circuit and the orientation of the wires determines the results.
Using Faraday's law on the resistive loop, integrating E dot dl around the loop doesn't equal zero.
But what happens if we instead remove the restive ring but leave the probe wires connecting to the same two points in space connected to nothing? Do we measure nothing?
I'm thinking you have no current path through the meter, so you you measure nothing.
I do want to do this continuous resistive ring as a physical experiment, but i first need to figure out the correct way to probe this.
I do want to do this continuous resistive ring as a physical experiment, but i first need to figure out the correct way to probe this.
However, if we change the position of the voltmeter and of the leads we are going to have whatever voltages we want between 0 and 1V, in absolute terms.
So what do we take from that?
Kirchhoff doesn't always hold.
No. We can't measure whatever voltage we want between 0 and 1V.
You shall check model of ring split ring into 10 parts or 4 parts each having 1/4V and 1/4R accordingly. BTW we talked about such case in this thread already.
Now to the part of KVL not holding any more: it seems people have different understandings of what KVL means. If you know it as "summed up voltages across a loop in a circuit are zero" then _yes_ it does not hold in this case. Because in the experiment shown by Dr. Lewing the voltages do not sum up to zero.
And I will trust him when he says that at MIT they did the experiment with superconductors _which cannot have an electric field inside them_ so there is no voltage across the "ring" that magically makes KVL hold.
Almost right. If the emf is 1V, with equal resistances in the loop you can measure any voltage you want between -0.5V and +0.5V.
Trying to localize in lumped components an inherently distributed phenomena will lead you to contradictions. Trust me, I know because I too did it, before seeing the light. :-)
If you take a ring of superconducting material and connect it to a resistor at one side, the voltage across the resistor will read whatever is appropriate according to faraday. If, however, you measure across the superconducting ring you will read 0 Volts.
Yes.
Edit: Now I'm sorry, this is not a chat but a forum so i should probably explain myself a little. What you get from faraday is the voltage *across the closed loop*. So thats Superconducting Ring + Resistor. From the resistance of the total loop (which is 0R for super conductor + resistance of resistor) you calculate the the current. Now take the resistance of the super condcutor, which is 0, and multiply it with the current. You will get 0V across the super conductor.
"Prove it"
That's what Lewin did.
Yes.
Edit: Now I'm sorry, this is not a chat but a forum so i should probably explain myself a little. What you get from faraday is the voltage *across the closed loop*. So thats Superconducting Ring + Resistor. From the resistance of the total loop (which is 0R for super conductor + resistance of resistor) you calculate the the current. Now take the resistance of the super condcutor, which is 0, and multiply it with the current. You will get 0V across the super conductor.
Oh, really? When it is convenient, you just forget about EMF.
We take 1.0V battery with 0.001 Ohm internal resistance, connect it to 1 Ohm resistor. 1A current will flow. Now take the resistance of the battery which is 0.001, and multiply it with the current. Result is 0.001V. So battery miraculously is not 1V anymore but 0.001V? :palm:
I did not forget about EMF, how do you come to that conclusion? Faraday gives us the voltage across the closed loop. You have a loop consisting of 2 components, one is superconducting and will not have any voltage across it. The other is a resistor, which can have a voltage across it if there is current flowing through it. So, naturally, all voltage in the circuit will be across the resistor.
I did not forget about EMF, how do you come to that conclusion? Faraday gives us the voltage across the closed loop. You have a loop consisting of 2 components, one is superconducting and will not have any voltage across it. The other is a resistor, which can have a voltage across it if there is current flowing through it. So, naturally, all voltage in the circuit will be across the resistor.
"all voltage in the circuit will be across the resistor" .. where superconductor loop terminals are connected meaning same voltage will be present on the both ends of the loop as well. So you do not measure different voltages by manipulating with test leads, this is dumb. Actual effect of test lead placement is explained in the document linked here so many times already.
You can't do that with changing magnetic fields. Curl-E = -dB/dt, so there is no scalar potential that describes electron motion. That is what Walter Lewin was showing. Everything else is just noise.
Yeah, but that "noise" is a very big claim that two points on the same circuit measure differently, he states that as a fact and uses a flawed demonstration to try and prove it. This is why many people have a big problem with this.
I did not forget about EMF, how do you come to that conclusion? Faraday gives us the voltage across the closed loop. You have a loop consisting of 2 components, one is superconducting and will not have any voltage across it. The other is a resistor, which can have a voltage across it if there is current flowing through it. So, naturally, all voltage in the circuit will be across the resistor.
"all voltage in the circuit will be across the resistor" .. where superconductor loop terminals are connected meaning same voltage will be present on the both ends of the loop as well. So you do not measure different voltages by manipulating with test leads, this is dumb. Actual effect of test lead placement is explained in the document linked here so many times already.
No, this is precisely what this is all about. If you measure at the same two points of a circuit you can get different readings on a voltmeter in the presence of an EMF. The reason this is the case and is *not dumb* is that in the presence of EMF the electric field is not a conservative vector field. Your voltage will vary depending on which path you take.
You want to know the voltage across the superinductor, you integrate along a line through the superconductor. Your voltage will be zero, because inside an ideal conductor the electric field is always zero.
You want to know the voltage across the resistor, you integrate along a line through the resistor. Your voltage will not be zero.
ogden, first I want to point out that SPICE is for simulating, not for proving.
Second, SPICE is not aware of the electric and magnetic fields.
ogden, first I want to point out that SPICE is for simulating, not for proving.
Second, SPICE is not aware of the electric and magnetic fields.
I did not ask to prove Maxwell's equations using SPICE :palm: Before you even consider to spread your wizdom, you really shall read what we actually were talking about.
As for your attempt to model a distributed circuit (where voltage is non single-valued) with a lumped circuit (where voltage is single-valued) to show that voltage is not multi-valued, I guess it's logically flawed.
Solve the mesh circuit with the emf, do the math. You will see the light.
Almost right. If the emf is 1V, with equal resistances in the loop you can measure any voltage you want between -0.5V and +0.5V.
Yes, current induced in the measuring wires.
Solve the circuit shown in Lewin's "Science and believing are different things", do the math.
Now I am no longer convinced you will see the light, but it's still worth a shot.
QuoteNo. We can't measure whatever voltage we want between 0 and 1V.
Almost right. If the emf is 1V, with equal resistances in the loop you can measure any voltage you want between -0.5V and +0.5V.
This is a good thread to ask. Does anyone know the original publication of these two Kirchoff laws 1st and 2nd, not voltage and current laws as usually wrongly tittled.
EDIT to answer the post below: I am not your tutor. Lewin has already solved it in his video
Your problem is even worse from the standpoint of spice simulation, because everything is distributed but still, off the top of my head, the voltage between two points forming an angle alpha with the center will be different when you measure it from one side out of the loop |V| = (alpha/2pi) * emf and from the other side of the loop |V| = (2pi - alpha)/2pi * emf (you need to fix the signs).
Where did I lose the resistance? I didn't. If the emf is 1V, the current is 1V/1ohm = 1amp.
Why do you think the measured voltage should depend on the value of the resistance? Is it not a uniform resistance loop?
What do you expect by raising the total resistance to 2 ohms?
also with 1V emf, and the measure points on a diameter, you will measure -0.5V on one side, from outside the loop, + 0.5V from the other side
"Each half of the loop is 0.5V EMF generator"
EMF on half loop?
What's next? Magnetic monopoles?
I am sorry, I can't help you fill those gaps.
Continue facepalming.
Just watched "Science and believing are different things", did the math. Left meter reads -900mV, right 100mV. In both - calculation and "lumped simulation". Funny that LTspice does not scream at me ;)
Can you please highlight on the circuit the two (2) nodes that give two different values of voltage between them?
These are all abstraction tools. Some tools you pick for some jobs. Some tools you pick for others.
The explanation video promised by Prof. Walter Lewin.
https://www.youtube.com/watch?v=AQqYs6O2MPw (https://www.youtube.com/watch?v=AQqYs6O2MPw)
Can you please highlight on the circuit the two (2) nodes that give two different values of voltage between them?So you are believer.
What a waste of time indeed.
And if your aim was to find an equivalent lumped circuit where you could see 0.1V and 0.9V you should have not bothered to add all those inductances.
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=572381;image)
In Section 30-6 we saw that we cannot define an electric potential for an
electric field (and thus for an emf) that is induced by a changing magnetic flux.
This means that when a self-induced emf is produced in the inductor of Fig. 30-13,
we cannot define an electric potential within the inductor itself, where the flux
is changing. However, potentials can still be defined at points of the circuit that
are not within the inductor-points where the electric fields are due to charge
distributions and their associated electric potentials.
Moreover, we can define a self-induced potential difference VL across an
inductor (between its terminals, which we assume to be outside the region of
changing flux). For an ideal inductor (its wire has negligible resistance), the magnitude
of VL is equal to the magnitude of the self-induced emf EL.
If, instead, the wire in the inductor has resistance r, we mentally separate the
inductor into a resistance r (which we take to be outside the region of changing
flux) and an ideal inductor of self-induced emf EL. As with a real battery of emf
E and internal resistance r, the potential difference across the terminals of a real
inductor then differs from the emf. Unless otherwise indicated, we assume here
that inductors are ideal.
There is indeed 0.9V and 0.1V on those resistors, it's Ohms law after all.
Where I stop agreeing is the claim that the mid point of the circle is both at 0.9V and 0.1V at the same time.
It's only at those voltages at the ends of the wire where it touches the resistors, but the voltage gradualy changes between the two as you move the measurement point along the wire. So i thing the experiment is misleading in the way it is explained.
The first equation is Kirchhoff's KVL law. In words, "the sum of all voltages in a closed loop = zero".
However I still don't agree with the demo experiment. But I do agree with some of it. There is indeed 0.9V and 0.1V on those resistors, it's Ohms law after all. Where I stop agreeing is the claim that the mid point of the circle is both at 0.9V and 0.1V at the same time. It's only at those voltages at the ends of the wire where it touches the resistors, but the voltage gradualy changes between the two as you move the measurement point along the wire. So i thing the experiment is misleading in the way it is explained.
Inside a source of emf that is open-circuited, the conservative electrostatic field created by separation of charge exactly cancels the forces producing the emf. Thus, the emf has the same value but opposite sign as the integral of the electric field aligned with an internal path between two terminals A and B of a source of emf in open-circuit condition
Voltage is the difference in electric potential between two points. The difference in electric potential between two points (i.e., voltage) in a static electric field is defined as the work needed per unit of charge to move a test charge between the two points.
So to measure from A to B, arrange your leads vertically so they are parallel to the magnetic field and perpendicular to the E field. Or in some other way shield the leads from the fields.
So now apply Faraday's law. First integrate the flux over the surface of your measurement loop. There is no net flux through the area surrounded by the measurement leads and the line from A to B, because of the way the wires are arranged or shielded.
You are splitting the loop in half, so they each have the same flux which is half the total flux. So either way you pick, there is an EMF of 0.5V. Then integrate around the path of the measurement leads and either half of the loop. If you go one way, you get 0.5V-0.1V=0.4V. If you go the other way, 0.9V-0.5V=0.4V. OK. So the true voltage is is 0.4V.
And yes, if you move the test points toward one of the resistors, you would "slice the pie" of the surface of the current loop differently, and the voltage you measured would continuously change and end up just the voltage across the resistor.
So your model, using lumped coupled coils or transformers, works. It gives you the "true" answer. I get it. It agrees with Electroboom and it agrees with Faraday's law. There's nothing wrong with it.
This is basically the same thing bsfeechannel did in his analysis back in reply #106. Some of the reactions were "you are just picking a path that gives you the answer you want".
But based on the standard way that electrical engineers look at measurements, this is the correct path. Again, fair enough.
edit: And yes, if you choose this path, the resistive ring always measures 0V.
So to measure from A to B, arrange your leads vertically so they are parallel to the magnetic field and perpendicular to the E field. Or in some other way shield the leads from the fields.
So now apply Faraday's law. First integrate the flux over the surface of your measurement loop. There is no net flux through the area surrounded by the measurement leads and the line from A to B, because of the way the wires are arranged or shielded.
I am not sure to understand this.
You do know that the flux depends on the area orthogonal to the field that is enclosed by the contour, right?
How on earth do you plan to place or shield your leads to avoid intercepting the flux when you are partitioning a disk? You should shield the area, but then forget connecting to a circuit immersed in the field.
For shielding, I was thinking more like coaxial shields around the test leads.
For shielding, I was thinking more like coaxial shields around the test leads.
Just put whole experiment into transformer core like this:
(http://www.edn.com/ContentEETimes/Images/01Steve%20T/LivAnaPotCores140/Pot%20Cores%201.jpg)
Dr. Lewin just uploaded another video.
Okay our voltmeters suck... so really what is the problem?
The experiment is never explained how the voltmeter 'selects' what voltage it can see. There is no mention given to the importance of the path that the voltmeters probe wires take and why they are routed in that exact way. It just leaves you head scratching how is it possible to see two different voltages at the same point. It demolishes your intuitive notion of voltage in circuits. Many electronics engineers after university are likely still confused as to how it works.
Okay our voltmeters suck... so really what is the problem?
The experiment is never explained how the voltmeter 'selects' what voltage it can see. There is no mention given to the importance of the path that the voltmeters probe wires take and why they are routed in that exact way. It just leaves you head scratching how is it possible to see two different voltages at the same point. It demolishes your intuitive notion of voltage in circuits. Many electronics engineers after university are likely still confused as to how it works.
Most simply don't care ;D
Okay our voltmeters suck... so really what is the problem?
The experiment is never explained how the voltmeter 'selects' what voltage it can see. There is no mention given to the importance of the path that the voltmeters probe wires take and why they are routed in that exact way. It just leaves you head scratching how is it possible to see two different voltages at the same point. It demolishes your intuitive notion of voltage in circuits. Many electronics engineers after university are likely still confused as to how it works.
Most simply don't care ;D
Well to be honest i wouldn't be surprised. Most people in university just memorise things to pass the test and are not even interested in understanding it.
It takes lots of enthusiasm for electronics to really get yourself to understand the field.
...And then they become walkers searching lost beans in some corporation, ruining everyones work with their idiocy.
Well to be honest i wouldn't be surprised. Most people in university just memorise things to pass the test and are not even interested in understanding it.
It takes lots of enthusiasm for electronics to really get yourself to understand the field.
Yeah, and those are probably the ones jerking off the most about how they are STEM educated and making fun of any non-STEM students during university. Which is funny, because if you just leave all the complicated stuff out of EE you can break it down to get pretty simple in practice.
I still don't think Lewin uses the right way to make his point nor quite the right examples
, but I must admit he at least opened our eyes on something we tend to use without actually really *caring* about all the underlying theory, as Dave said. When we do our work properly, it still doesn't change anything much, but now we know we don't use KVL the way it was intended, and that our definition of "voltage" is in all aspects more practical than theoretical.
Maybe a bad analogy?
It's like trying to argue that Newtons laws are "for the birds" and are just a special case of general relativity. You aren't wrong by saying that, but geeze, try going into NASA and telling all the space probe engineers that Newtons laws are "for the birds", you'd get laughed out of the room.
Bad probing is the result of performing a measurement of a desired quantity in such a way that the resulting measured value differs from the actual value of the quantity by more than than our defined error margin allows for.
Seems to me it's simple to resolve, put the meter HALFWAY and see what you read...
Seems to me it's simple to resolve, put the meter HALFWAY and see what you read...
When you do that, what are you supposed to read? Because there's two different resistors in parallel that are in series too, with the same current going through both... I*R1? -I*R2?
KVL is not a special case of Faradays law even if it looks similar. Instead it is a tool used in analysis of abstracted schematic circuits. If you are to unravel all of these mathematical circuit modeling tools far enough you would eventually get to Maxwells equations, but its not as simple as sticking an extra voltage into KVL, you would end up with multiple pages of math before you get there. Our circuit schematics are the equivalent of "spherical cows in vacuum" in physics, its an abstraction that optimizes and simplifies the math for quick and easy computation. In physics the well known F=m*a equation(Often called Newtons 2nd law) is also wrong in certain cases (Rockets and mass–energy equivalence) and we still use it with its limitations in mind rather than saying its for the birds.
So is it bad probing? I think we need a definition of what that is first. Its hard to find a formal definition of it but lets say we use something like this:QuoteBad probing is the result of performing a measurement of a desired quantity in such a way that the resulting measured value differs from the actual value of the quantity by more than than our defined error margin allows for.So by this definition Dr. Lewin is not doing bad probing since he is indeed measuring the voltage he is after within tolerances required by the particular demonstration.
It's kinda similar with that "current flowing through a capacitor" video. Electrons don't actually flow through the capacitor, but that interpretation along with AC impedance is the practical and easiest way to design and analyse circuits and that's why it's used and is a perfectly valid way of thinking. Ironically, it's Maxwell's displacement current theory that helps validate the concept here. So the deeper into the theory you go, the more it backs up the "incorrect" current flow viewpoint.
Let’s look at when are Kirchoff’s Laws would be violated. Notice that both laws assume the
time rate of change of something is approximately 0. This means they are true in the ‘static’
or ‘low frequency’ limit. The circuits that you will deal with in this course work under this
limit. However, it’s interesting to note that KCL is violated inside the capacitor because
charge can build up on the capacitor plates, so if part of your closed surface passes between
the plates the net charge changes significantly with time. However if you consider the
capacitor as a whole ‘lumped element’ and include both plates inside the closed surface, the
charges on opposite plates cancel out and KCL will still work. Similarly, KVL is violated
inside the inductor because a significant magnetic flux passes through the coil, so if your
closed path runs along the coil’s wiring a voltage drop occurs even across the perfect metal
wire. However if you consider the inductor as a whole ‘lumped element’ and recognize its
total voltage as the induced electromotive force due to Lenz’s Law, KVL will still work.
If two meters that are part of super experiment circuit shows 0.1V and 0.9V accordingly, then such "halfway" meter shall read 0.4V.Seems to me it's simple to resolve, put the meter HALFWAY and see what you read...When you do that, what are you supposed to read? Because there's two different resistors in parallel that are in series too, with the same current going through both... I*R1? -I*R2?
It is discussed/explained in this thread many times by the way
It's -0.1V and 0.9V.
Oh, oh, ok. This, but with only one voltmeter in the center:
Yes, not only is KVL for the birds, but KCL is too!
The reason we are arguing about KVL is that Dr. Lewin is trying to apply KVL to electric fields rather than circuits and is then blaming KVL for being wrong just because he is using it wrong.
Dr. Lewins circuit with two resistors and a mysterious current forced trough it without having a circuit component doing the actual current pushing. It breaks the circuit abstraction by doing things that are not supposed to happen and as a result breaks the math used to analyze circuits (Like KVL).
He is a physicist and has likely not done enough circuit analysis and modeling to see that KVL is not just Faradays law with a missing voltage.
He is not using it wrong. And you say so, too:
Yes, KVL works for lumped circuit abstraction only. When the premises for lumped circuit analysis are missing, KVL is for the birds.
No. In order to see KVL as Faraday's law with a missing voltage, lumped circuit assumptions need to be met. All fluxes should be confined inside the lumped components and you should not be allowed to run circles around them. It's as easy as that. No refinement of the theory (the concept of inductance used in the 'extended KVL' you mention is based on Faraday's law), no need to add parasitics, no nothing.
An engineer should know the limits of their tools and theories.
KVL is lumped circuits stuff. Circuit not lumped ----> KVL for the birds.
Edit: changed highlighted part, able->allowed
And what can electroboom say in reply, now?
Can you show me a source that claims that KVL is allowed to be used outside of lumped cirucit schematics? And if it does use it as a simplified version of Faradays law does it ever say its valid in a non DC scenario?
Because he is analyzing a circuit that is NOT LUMPED. He is INSIDE the frigging coil!!!
He is not using it wrong. And you say so, too:
Can you show me a source that claims that KVL is allowed to be used outside of lumped cirucit schematics? And if it does use it as a simplified version of Faradays law does it ever say its valid in a non DC scenario?
An engineer should know the limits of their tools and theories.
KVL is lumped circuits stuff. Circuit not lumped ----> KVL for the birds.
An engineer should know the limits of their tools and theories.
KVL is lumped circuits stuff. Circuit not lumped ----> KVL for the birds.
And that is the entire reason why Dr Lewin's experiment is flawed. He's trying to use a practical lumped circuit to show how his non-lumped "inside the inductor" Faraday thinking is right.
And that's wrong, or at best misleading, even though what's he's saying and explaining is not wrong.
An engineer should know the limits of their tools and theories.
KVL is lumped circuits stuff. Circuit not lumped ----> KVL for the birds.
And that is the entire reason why Dr Lewin's experiment is flawed. He's trying to use a practical lumped circuit to show how his non-lumped "inside the inductor" Faraday thinking is right.
And that's wrong, or at best misleading, even though what's he's saying and explaining is not wrong.
>>>asks me to find a mistake on my own>>Edit: typos (some of them) and added part on equations on board.
that is by far the best way to teach Trust me I have been teaching Physics for 58 years. If present a student on a silver plate what (s)he did wrong they will quickly forget. But if they have to put in the effort to find their mistake (after I have sent them my lectures which address their topic) they will never forget.
Lewin is not using KVL wrong, because he is not using it. He is using Faraday. Watch his video "Science and believing..." and follow the mesh analysis. You might have been confused by the fact that he drew what appears to be a circuit with lumped elements (and in fact, many posts ago, I said "I am not calling it schematics on purpose") but thatcurly arrowmagnetic field representation inside the central mesh is telling it all. He is using Faraday.
And, in fact, he is getting path depending voltages.
No incongruences whatsoever.
And why is he using Faraday and not KVL?
Because he is analyzing a circuit that is NOT LUMPED. He is INSIDE the frigging coil!!!
If you insist in using KVL, for example at the mesh with the two voltemeters, you find and impossible result.
Impossible for Kirchhoff, but not for Faraday.
As for the rest of your post, I sense confusion. I don't know how to say it. KVL works only in the lumped component assumption. Real world components like inductors, coupled coils and transformers can be modeled with lumped components AS LONG AS YOU DO NOT MESS WITH THEIR FLUXES. In this case you can mend KVL in 'generalized KVL'.
If in your circuit you are able to mess with the flux, say goodbye to KVL and 'generalized KVL'. You need to apply Faraday, or you will find inconsistent results.
There is, therefore, no 'practical lumped circuit'. Neither in the real world, nor on the blackboard (or whiteboard).
Summary:
1. Title is "my sincere apologies"
2. 90% of video is arguing against the nonexistent strawman who is apparently suggesting that Farady's law is incorrect, and Kirchoffs is always correct. Take great glee in squashing this strawman by repeating the same thing he has stated like a broken record for the past week.
3. State that anyone with a masters in electronics who suggests that the different readings are only* due to placement of the probing leads is an idiot.
4. Clarifies that the "sincere apology" is for being too blunt in laying out his 100% correct argument against the fairy tale strawman while completely brushing off the actual point of contention.
*but let's forget that I was the one to apply real oscilloscpes and their readings to a real test circuit. If we applied these real oscilloscopes to my theoretical model, we would apparently learn that [start broken record]
Super shorter summary:
"I can see the sailboat, and you can't."
Next up:
"Newton's laws are just a special case of relativity. It's a crime that we call these things laws, when it is really Newton's Loopholes."
You have to remember that Electroboom is making a really really bad claim here. Electroboom is claiming that induction in the probe wires is what causes the result.
Sorry but Mehdi got owned here.... if he is going to do a video like that he should brush up first. As Lewin said, this is embarrassing for him.
b) KVL in non lumped circuit: He is wrongfully applying KVL to a non lumped circuit so it does not work because its not meant to work
Mesh analysis is a big part of the circuit analysis toolkit and is used on lumped circuits. This is another reason why i get the feeling he is mixing lumped and real circuits as if they are the same thing.
As soon as you draw a resistor symbol you are creating a lumped model of a resistor.
So rather than saying KVL is wrong he should have said ether "KVL can't be applied here because this is not a lumped cirucit" or "Here is a lumped equivalent circuit that is required to apply KVL"Good if you want your students to think in a compartmentalized way. Like technicians. But if you are forming scientists, or even engineers, you should teach them to question the limits of the tools (practical and theoretic) they use.
Yes that is the main point of using a lumped circuit. You don't have to mess with the fluxes.
[...]
The only case where i can see lumped models of wires being a bad idea is when the wires are physically moving during the circuits operation.
Nobody is stopping you from only analyzing circuits with non lumped models, but don't expect anyone else to do so. Most people enjoy calculating the result in a few lines of math rather than a few pages (And still get the same result).
You just embarrassed yourself - because induced EMF in the probe wires is actual cause of "surprising" result. Dr.Lewin explains it in the video "Believing and Science are Very Different".
He overall main mistake is that for some reason he thinks voltage must exist across the wire portion of the induction loop.
In all seriousness... has anyone checked this guy even is actually qualified? Is it just a show? His videos are entertaining but his video on this is absurd junk science. What is scary is the amount of people on here, and youtube, and reddit, who are siding with Mehdi...
It's not KVL, it's Faraday.
I called it mesh analysis to make the sentence short. And in fact he is analyzing the meshes, applying Faraday. Where's the big difference with lumped circuit analysis? That the emf is not localized. This is best seen when you bring the voltmeter inside the loop and you probe the points on a diameter. Now, if you use Faraday and the emf is not localized, the emf contribute appears in BOTH sub-meshes, proportional to the area encircled by the sub-mesh. If you localize it as if it were a lumped circuit, the emf contribute appears only in one sub-mesh, no matter the area.
And where is it written that that lumpiness is contagious?
Come on, what should he have done? Invent a new symbology? I've never seen that in any of the EM books I've read.
You should have enough mental flexibility to understand what is going on.
Lewin's circuit IS A CASE WHERE A LUMPED MODEL IS INAPPROPRIATE.
How can this be so hard to grasp?
Seriously? After all these umptillion pages of discussion you still have not realized that Lewin's circuit cannot be analyzed with lumped circuit theory?
Nobody is saying that you have analyze all circuits with 'non lumped models' only. You just have to do that only when it is necessary. Such is the case of Lewin's circuit.
Oh, for the love of... Physics! :-)
I have created a lumped element model that behaves identically to Dr. Lewins experimental circuit on the first page of this thread:
https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/msg1945312/#msg1945312 (https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/msg1945312/#msg1945312)
Your model DOES NOT BEHAVES IDENTICALLY to Dr. Lewins experimental circuit.
In Lewin's circuit you can have two different voltage readings from the VERY SAME TWO NODES.
Your circuit cannot do that. You get two different reading from TWO DIFFERENT COUPLES OF NODES. I do not even have to check it because I know that Spice can not tolerate that kind of ambiguity. I have already written about it, some twelve billions posts ago. And if you want to see -0.1V and 0.9V on those two resistors, you could have placed just one coil, with the two resistors in series. Et voilà, the magic dual reading. Except it isn't referred to the same two nodes.
Also, note that the 'extended KVL' is just Faraday under disguise. The original KVL cannot even account for lumped inductances and trasformers. It is indeed for the birds when you have these kind of components in the circuit. But we can still save the appearances by moving the emfs on the other side and pretend it's a voltage drop or a voltage generator (so to speak) and happily simulate our circuits in Spice - it won't scream at you because in this case you can still have single-valued potentials.
But that WORKS only if the components are lumped, i.e. you do not mess with their fluxes. When you can mess with the fluxes, you can no longer pretend to have lumped components, so even the extended KVL is for the birds - you need to account for the distributed emf 'manually'. You can simulate a different, similar circuit in Spice to help out in solving the equations, but you won't see that magic trick of the voltage across the very same two points assuming different values at the same time.
Come back when Spice can give TWO different voltages from the very same TWO NODES. Not three, not four. TWO.
I'll be waiting for you in my igloo in Hell.
In any case the key point is: having voltages depending not only on the endpoints but also on the path, is no magic at all. It is basic electromagnetism - it is a behavior that goes down to the bone of EM structure. Starting from the definition of rotor, passing through Stokes theorem and adding in a pinch of experimental result (Faraday's law).
And that is really basic physics.
The voltage across the meter reads 0V.
This video at 9:30 shows this experimentally:
So when do i get to see a real life voltmeter showing two voltages?
So when do i get to see a real life voltmeter showing two voltages?
I'm not sure why sectokia posted a link to this video, then deleted his posts.Because it kind of proves EB right, contrary to his critique?
I was wrong.
Lewin is the fraud.
I'm not sure why sectokia posted a link to this video, then deleted his posts. But I think it's worth watching if you are interested and have half an hour to kill.
Some people will say he found the proper way to make this measurement. Others will say that he is just choosing a measurement path that gives him what he wants:
https://youtu.be/JpVoT101Azg (https://youtu.be/JpVoT101Azg)
So when do i get to see a real life voltmeter showing two voltages?
I see you excluded going around the flux. Naughty boy! :-)
But I can do this with an arm tied behind my back. Bring the voltmeter inside Lewin's two resistors loop, solder its probes on opposite points on the diameter. Wiggle the probes around.
There you go. You can read anything you like from -0.1V to +0.9V (ok, it's either AC or pulsed so the sign is more about phase in the AC case).
Don't tell me you want to see a voltmeter giving two readings from the same two points and the same path.
Am I the only one sensing a shifting goalpost, here?
I am afraid I cannot help you further in solving your confusion. All I can do is suggest you read Ramo, Whinnery, Van Duzer. It will clarify a lot about lumped circuits, distributed circuits and field analysis for waveguides, resonant cavities and antennas. There's a whole world out there, beyond Kirchhoff's columns.
I'm not sure why sectokia posted a link to this video, then deleted his posts. But I think it's worth watching if you are interested and have half an hour to kill.
Some people will say he found the proper way to make this measurement. Others will say that he is just choosing a measurement path that gives him what he wants:
<YOUTUBE>
:-// If you really want to see it in real life, your best bet may be to take a few minutes and set it up yourself. If you lived next door, I could invite you to see my setup in person. Dr Lewin did make a video using volt meters as well as a scope but I can understand wanting to see it for yourself. Some wire, a bolt, battery, couple of resistors and a couple of cheap analog meters.
I'm not sure why sectokia posted a link to this video, then deleted his posts. But I think it's worth watching if you are interested and have half an hour to kill.Great video. Well worth watching.
Some people will say he found the proper way to make this measurement. Others will say that he is just choosing a measurement path that gives him what he wants:
https://youtu.be/JpVoT101Azg (https://youtu.be/JpVoT101Azg)
He also understands how Maxwell-Faraday interacts with reality too rather than just seeing it as an equation.
He credits someone called Kirk McDonald for his explanation of the "Lewin paradox".
3) Dr. Lewin is right about everything in his videos except his claims about KVL are wrong.
In all seriousness... has anyone checked this guy even is actually qualified? Is it just a show? His videos are entertaining but his video on this is absurd junk science. What is scary is the amount of people on here, and youtube, and reddit, who are siding with Mehdi...
I think it's far more alarming that people ridicule the desire to understand and learn, and start talking in "siding with" terms when a younger engineer wants to question a professor and ask for clarification in order to gain and spread understanding, and does it in a completely civil way, with a lot of more thought and actual experiments put into it than what goes to usual lecture question. I would be extremely happy for such well-formed and scientifically sound questioning from someone outside the formal scientific circles.
Even more alarming is that an academic person who has been actually teaching is completely unable to handle this kind of situation, which should be everyday practice when it comes to science and learning.
He also understands how Maxwell-Faraday interacts with reality too rather than just seeing it as an equation.
The equation summarizes reality. That's why you, I and everyone in this forum need to study Maxwell.
Maxwell didn't come up with his equations out of an exercise of math. He collected experimental data from Faraday, Ampere and Gauss, tried to figure out what was going on, i.e., what the REALITY was, and proposed the equations that better describe it.
More important, after he grasped the deep meaning of that REALITY, he could predict, among other amazing things, the existence of something that REALITY was not making so obvious in his time: the propagation of radio waves.
Fifteen or so years later Heinrich Hertz proved with an EXPERIMENT that the equations were right.
When you see people treating Maxwell just "as an equation" it is because they understand the solidity of the theory, have proved its efficacy in practice and have absolute confidence in its predictions.
Instead of taking this opportunity to show the limitations of Kirchhoff and encourage people to learn Maxwell, people are transforming the discussion into a libel against the old professor.
but Mehdi's not responsible for other "people" transforming the discussion into any "libel".
But I think it's worth watching if you are interested and have half an hour to kill.
To say there is "EMF in the wires" makes no sense. According to Faraday's law, in this case the EMF is the time rate of change of the magnetic flux through a surface. The surface defines the EMF. It is not located at specific points in the path that defines the surface.
I'm saying this is Faraday's law:To say there is "EMF in the wires" makes no sense. According to Faraday's law, in this case the EMF is the time rate of change of the magnetic flux through a surface. The surface defines the EMF. It is not located at specific points in the path that defines the surface.
Wait... So you say that there is no EMF induced in the straight wire which is located in the changing magnetic field and only complete/closed loop results in EMF?
To say there is "EMF in the wires" makes no sense. According to Faraday's law, in this case the EMF is the time rate of change of the magnetic flux through a surface. The surface defines the EMF. It is not located at specific points in the path that defines the surface.
Wait... So you say that there is no EMF induced in the straight wire which is located in the changing magnetic field and only complete/closed loop results in EMF?
Those is not just a theoretical thing. It is verifiable. If there was an emf there would be a static build up at each end of the wire that you could measure the e field of. But there isn't. It only becomes measurable when you close the loop. If you close it with a resistor there is a static build up on either side of it that you can measure.
Those is not just a theoretical thing. It is verifiable. If there was an emf there would be a static build up at each end of the wire that you could measure the e field of. But there isn't. It only becomes measurable when you close the loop. If you close it with a resistor there is a static build up on either side of it that you can measure.
I think the charge moves in the wire even if it's not a closed loop, if you could measure it you'd see a + q in one end and a minus q in the other end.
I think the charge moves in the wire even if it's not a closed loop, if you could measure it you'd see a + q in one end and a minus q in the other end.
I think the charge moves in the wire even if it's not a closed loop, if you could measure it you'd see a + q in one end and a minus q in the other end.
And which end will have a plus and which will have a minus?
Imagine your AB segment in a uniformly distributed time-varying B field. It is all the same, spatially.
Which end will get the plus, and which end will get the minus?
Can't decide?
Well, let's create a square loop with AB as its side. Use the right hand rule to find out how the current will flow with that flux varying configuration. Now you can tell me which extreme of AB is plus and which is minus, correct?
Except...
That it all depends which 'side of the loop' AB is on.
Think of two square clocks with a common AB side. Is the seconds hand going up or down? Does it depends on which clock the hand belongs to?
I think the charge moves in the wire even if it's not a closed loop, if you could measure it you'd see a + q in one end and a minus q in the other end.
And which end will have a plus and which will have a minus?
Imagine your AB segment in a uniformly distributed time-varying B field. It is all the same, spatially.
Which end will get the plus, and which end will get the minus?
Can't decide?
Well, let's create a square loop with AB as its side. Use the right hand rule to find out how the current will flow with that flux varying configuration. Now you can tell me which extreme of AB is plus and which is minus, correct?
Except...
That it all depends which 'side of the loop' AB is on.
Think of two square clocks with a common AB side. Is the seconds hand going up or down? Does it depends on which clock the hand belongs to?
Sure you can decide. You follow the usual rules of direction with magnetic fields.
This example shows the wire moving trough the magnetic field, but you can just as well keep the wire stationary and move the magnetic field instead.
And you are the one who does not shift goalposts, eh?
There is no motional emf in Lewin's circuit.
In your example, the velocity of the moving bar is breaking the symmetry.
Please answer the question:
How do you decide which extreme of the bar has the plus and which has the minus when your bar is STATIONARY with respect to a SPATIALLY UNIFORM but TIME-VARYING B field?
Are you capable of answering THIS question without changing the problem?
EDIT: As for the antenna example, of course that breaks KVL as well, but we are trying to keep things simple here. So our circuit is in the domain of quasi-static electrodynamics, where the d/dt of the field is so small that the concatenation of B and E fields dies off in a very short distance. We are in fact disregarding the displacement current in Ampere-Maxwell's equation. So, no radiation.
How do you decide which side is plus and which is minus in the case of a bar, stationary with a spatially uniform, time-varying magnetic field?
Same question applies to GeorgeoftheJungle, of course. He too did not answer.
How do you decide which side is plus and which is minus in the case of a bar, stationary with a spatially uniform, time-varying magnetic field?
Same question applies to GeorgeoftheJungle, of course. He too did not answer.
A varying magnetic field pushes q in one direction, that's how you know where q is going to move to. Berni has even drawn it for you. What am I missing?
How do you decide which side is plus and which is minus in the case of a bar, stationary with a spatially uniform, time-varying magnetic field?
Same question applies to GeorgeoftheJungle, of course. He too did not answer.
A varying magnetic field pushes q in one direction, that's how you know where q is going to move to. Berni has even drawn it for you. What am I missing?
Yes but that picture is not very helpful for a varying uniform field. When you have a varying non uniform field you get induction in that straight piece of wire because the field lines appear to be moving in relation to the wire.
When you have a varying uniform field its only the magnitude of the field that changes, the actual field lines stay in the same place. This field will try to push electrons in a circle around the field lines. This can be imagined as every field line trying to get electrons to circle around it at the same time. On a straight wire this makes the electron get pulled in both directions simultaneously since some field lines are on one side and some on the other side of the wire. Once you put a bend in the wire this makes the electrons easier to move in the direction the wire is bending. So as a result the fields on the outside of the bend are mostly pushing the electrons into the side of the wire while the fields on the inside of the curve are pushing electrons more along the direction of the wire. This makes the fields on the inside of the bend win out and start moving electrons along the wire according to the left hand rule.
Sorry if this explanation is not very scientific but i think it makes the concept easier to grasp.
You do realize you are making up rules on the fly, do you?
So, let me get this straight (pun intended).
Let's consider a square loop, with AB side perfectly straight. According to your model, there is no 'partial emf' on that side, right? And if you bend it a bit, the sign of the 'partial emf' will change according to the curvature of that side?
Or, let's just consider an AB segment alone: according to your rule: when it is straight there is no charge build up, but if it is bent in one way the charges are + on A and - on B, while if it is bent the other way the charges are - on A and + on B, correct?
Man, am I glad I do not live in the same universe as you. Looks pretty much more complicated than the universe I am in.
KVL breaks in the case of radiation, correct. But it also breaks in the case of induction.
Its not the curvature itself that causes voltage, but the overall trend the wire is taking. A square is still bending around to form a loop that creates the usual direction.
I will admit i don't fully understand the underlying magic that determines why things move in the specific directions inside fields but the overall effects this causes seam to point towards this.
I would love to live in a simpler universe but magnetic and electric effects are linked trough the effects of Einsteins relativity and that stuff does all sorts of weird things.
It looks like you are trying to say you can define emf only if you can identify an area to associate to it.
Well, that's progress. That's what Faraday has tried to tell you since the nineteenth century.
Correct, but not as weird as you think.
I suggest to brush up your physics on some good book, like Purcell (Electricity and Magnetism, second volume of the Berkeley physics series), and then look up the practical applications of the basic concepts in books like Ramo, Whinnery, VanDuzer (Fields and Waves in Communication Electronics).
As for the further goalpost shifting at the end of your post, please... Leave caps out - we are trying to keep things simple here. If we are having trouble understanding each other with a simple circuit like that, what do you think would happen if you introduce another paradox generating element, like the two caps back to back?
And no, KVL did not work with Lewin's circuit. You had to introduce that magical emf term to make your numbers check. That's Faraday at work. In fact, you cannot locate that voltage anywhere with a voltmeter, can you? I am talking about that circuit, do not try to modify it. Let down those scissors, I tell you!!!Its not introducing a magical emf out of nowhere.
EDIT: Repetitia juvant.
What happens if we pull the resistors out of the loop and make sure we cannot interfere with the flux that is generating the emf? That we have a series of two resistors and a black box with two terminals. Now you can call that the secondary of a hidden transformer. Now you can located the voltage it 'generates' with a voltmeter. It's right there, at its two terminals! Now you can delude yourself KVL works, and call it, instead of Faraday's Law, "extended KVL" or "modified KVL" or "modern KVL". Lumped circuit theory works, all voltages we can measure are uniquely defined. Now the quarrel "KVL vs Faraday" is just a language barrier.
But when the resistors are inside the loop, say goodbye to lumped circuit theory and uniquely defined voltages. You have to take paths into account.
I will admit i don't fully understand the underlying magic that determines why things move in the specific directions inside fields but the overall effects this causes seam to point towards this.
I would love to live in a simpler universe but magnetic and electric effects are linked trough the effects of Einsteins relativity and that stuff does all sorts of weird things.
I do have at least some understanding on all of those areas, just that some i don't know well in to the detail and especially not down into the deep math behind it. Its just not something i deal with on a regular basis. Electronics engineering has so many abstractions in place that there is no need to delve this deep into the fundamental math under it all. Hence why most electronics engineers know about Maxwell and what he did, but they never used his equations on the job. Its just easier and faster to use the derived "easy bake" equations for calculating everything you would need, but if you dig down and dissect a lot of those equations you tend to find some Maxwells equation somewhere in there.
Contrary to popular belief engineers are mostly not math geniuses, they are just really good at looking up the right equation and quickly punching it into a calculator. Its simply the fastest way to get work done on a deadline.
The explanation video promised by Prof. Walter Lewin.
https://www.youtube.com/watch?v=AQqYs6O2MPw (https://www.youtube.com/watch?v=AQqYs6O2MPw)
If we engineers deliberately neglect the fundamentals, how can we criticize Lewin who is teaching them?
If we engineers deliberately neglect the fundamentals, how can we criticize Lewin who is teaching them?
I would not call high level abstraction as negligence. It is common sense. We criticize Dr.Lewin because he neglect fundamentals himself (read "Lewin’s Circuit Paradox" by Dr. Kirk T. McDonald - you'll see). I do not see anybody who is against Maxwell's equations or saying that Kirchhoff's law *always* hold. Those who do not agree (to "KVL for the birds") say that Kirchhoff’s loop equations apply to Lewin’s circuit.
We criticize Dr.Lewin because he neglect fundamentals himself (read "Lewin’s Circuit Paradox" by Dr. Kirk T. McDonald - you'll see). I do not see anybody who is against Maxwell's equations or saying that Kirchhoff's law *always* hold. Those who do not agree (to "KVL for the birds") say that Kirchhoff’s loop equations apply to Lewin’s circuit.
So, you criticize Lewin because someone else wrote an article criticizing him? Not because you yourself master the fundamentals and is in a position to confront him? What kind of engineers do we want to be?
Just a bunch of dilettantes ranting at random in forums? Let's shut up and do our homework. Thank you.
I already provided my position here in this thread. That's why I just refer to article I agree to and do not repeat what is already said. Don't blame me if you did not read thread or do not remember what I did say or whatever.
Those who do not agree (to "KVL for the birds") say that Kirchhoff’s loop equations apply to Lewin’s circuit.
You better behave
Kirchhoff died absolutely ignorant of the confirmation of Maxwell's theory so that's why his theory doesn't account for that. Period.
Here's a dollar, kid. Go get yourself a better education.
Here's a dollar, kid. Go get yourself a better education.
So, you criticize Lewin because someone else wrote an article criticizing him? Not because you yourself master the fundamentals and is in a position to confront him? What kind of engineers do we want to be? Just a bunch of dilettantes ranting at random in forums? Let's shut up and do our homework. Thank you.
No they don't. Suppose that Kirchhoff didn't know about Faraday's law of induction. I show a loop of wire with two resistors and hide the solenoid under the table. I ask Kirchhoff to measure the voltages with a voltmeter. Kirchhoff wouldn't know how to explain how a loop of wire with two resistors and no voltage source has some voltage on them. Worse, he wouldn't know how to explain why the voltmeter shows diferent voltages depending on the position of the voltmeter.
Kirchhoff wouldn't know how to explain how two pieces of wire hanging out in the breeze (that today we call dipole antenna) suddenly have voltages and currents without no visible voltage source connected to them.
Although Faraday demonstrated the phenomenon of induction in 1831, he couldn't find a mathematical formulation and therefore his theories were rejected by the scientists of the time. Meanwhile in 1845 Kirchhoff came up with his law that do not account for any kind of varying field for that matter. In 1865, Maxwell could finally produce his now famous equations that gave a mathematical formulation to Faraday's law.
Kirchhoff died in october 1887. Hertz published his first paper confirming Maxwell's equations in november 1887.
So there is no paradox in Lewin's explanations. Kirchhoff died absolutely ignorant of the confirmation of Maxwell's theory so that's why his theory doesn't account for that. Period.
So who told you that the loop is a secondary of a transformer? Certainly not Kirchhoff. Because when that theory could finally be confirmed, he was DEAD. End of story.
Don't you see how detrimental this attitude is to science and understanding?
IMHO, this is also the actual mistake Lewin is making.
Honest questioning and discussion should be valued.
Not everyone is as strong as a person as you or me or ogden. Not everyone wants to fight. Some may actually get upset about they way Lewin arrogantly attacks their "qualifications" when they just asked honest questions, especially if you are in the role of a student. They won't ask more questions, but instead, do as you teach them to do: close up your desire for understanding, just shut up and "learn". But, just reading isn't the way you learn science. You need to really understand, and for that, asking questions, yes, even questioning your professor - would be the right thing to do.
But I guess we'll disagree on this. And, I think you are genuinely a bad person for not even trying to think about this side of the coin - and the life goes on :).
It just seams to me that Dr. Lewin has a different idea of what KVL actually is, this is what is leading him to the conclusion of KVL being just a special case of Faradays law with no magnetic field (Its not, you can't even stick an electric field into KVL).
Kirchhoff (KVL) IS a special case of Faraday.
What does Maxwell say? That the EMF along a closed line in space is a function of how the surface integral of a magnetic field across an arbitrary surface bounded by the closed line varies in relation to time.
The magnetic field can vary in intensity and direction. The surface can vary in size, direction and/or shape (including the closed line).
When that surfce integral does not vary with time, EMF is zero. And that coincides exactly with what Kirchhoff said: that the sum of the voltages around a mesh (a closed line) is zero.
In what circumstances does the surface integral equal zero? When the magnetic field AND the surface are constant, for example, among many other cases.
So Kirchhoff ended up being a subset Faraday. I even drew it as a Venn diagram many messages ago in this thread.
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=583322;image)
I did some experimentation with a stepped pulse instead of the nice Gaussian, but still working on that.
I really don't see how Kirchhoff's law could possibly be used to analyze something like this (and truly be successful).
So you need to apply a similar voltage step response across your solenoid coil (Not just a pulse).
I think is pretty standard for excitation pulses to be 1 Volt in these sims.
Yes this is what i find to be the issue. Faraday and Kirchhoff are put into the same basket while they describe different things.
Here is a definition of Faradays law:
"The electromotive force induced in a circuit by variation of the magnetic flux through the circuit is proportional to the negative of the time rate of change of the magnetic linkage"
Here is a definition of Kirchhoff voltage law:
"The algebraic sum of all the voltages around any closed loop in a circuit is equal to zero"
Kirchhoff on the other hand does talk about the voltages summing to zero. Notice that it says "all the voltages" so this implies induced EMF too as that's a voltage inside the loop.
In a circuit mesh schematic a wire has zero length, zero resistance and zero reactance. These wires are immune to all field effects. Building the two resistor circuit with such wires in the real world results in a circuit that must have a circumference of zero, this means it also must have a loop area of zero, zero area means no induced EMF and KVL works.
This however has a problem because Dr. Lewins circuit clearly has a loop area larger than zero so it makes the circuit mesh model act different(You get 0V on both resistors). We fix this by replacing out ideal wires with inductors.
This plugs in Faradays law and tells it about how big the loop area is.
YES I KNOW that Kirchhoffs voltage law does indeed break in certain special cases, i'm not saying it always works.
Can you explain in what way is it a special case of Faradays law, if the two laws describe two separate concepts?
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=583322;image)
That diagram i fully agree with. Kircchhoffs laws are an abstracted application of Maxwells equations and are meant to be only used on lumped circuit meshes.
Since the mid-20th century, it has been understood that Maxwell's equations are not exact, but a classical limit of the fundamental theory of quantum electrodynamics.
When Kirchhoff says all the voltages, he is not considering any kind of EMF.
If, however, you have a constant magnetic flux, Kirchhoff holds. So Lewin has no problem with Kirchhoff.
QuoteSince the mid-20th century, it has been understood that Maxwell's equations are not exact, but a classical limit of the fundamental theory of quantum electrodynamics.
from https://en.wikipedia.org/wiki/Maxwell%27s_equations#Limitations_for_a_theory_of_electromagnetism (https://en.wikipedia.org/wiki/Maxwell%27s_equations#Limitations_for_a_theory_of_electromagnetism)
you might have to fix your Venn diagram.
Does that mean Maxwell "is for the birds"?
That depends on the symmetry of the induced field. Let me give you my take on that paper (who appears to be a draft considering there is at least a minor error and a (?) meaning what, exactly? Do you know if this was ever published and where is the definitive version?)
Well, it's interesting but it is nonetheless amazing that to compute the emf on an open path, the area always pops out.
What happens if your EMF is ZERO? Doesn't that ring you a bell? Where did you see ZERO before?
Ahh! KIRCHHOFF! He says that "The algebraic sum of all the voltages around any closed loop in a circuit is equal to ZERO"!!!!!!!QuoteKirchhoff on the other hand does talk about the voltages summing to zero. Notice that it says "all the voltages" so this implies induced EMF too as that's a voltage inside the loop.
Here is where your problem lies. When Kirchhoff says all the voltages, he is not considering any kind of EMF. In Kirchhoff's wonderful world there is absolutely NO EMF whatso-fluxing-ever!QuoteIn a circuit mesh schematic a wire has zero length, zero resistance and zero reactance. These wires are immune to all field effects. Building the two resistor circuit with such wires in the real world results in a circuit that must have a circumference of zero, this means it also must have a loop area of zero, zero area means no induced EMF and KVL works.
Philosophical question: if Kirchhoff only applies to circuits that cannot exist, why do we need his stupid theory?Quote(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=583322;image)
That diagram i fully agree with. Kircchhoffs laws are an abstracted application of Maxwells equations and are meant to be only used on lumped circuit meshes.
You do not only have a problem with Kirchhoff, Maxwell and Lewin. You also have a problem with Georg Cantor.
Between you and me. Forget all you know about circuits. Follow the guidelines I published in a previous message. Study calculus, vector analysis and a good book on electromagnetism. You'd be better off than struggling with theories you do not master.
Physics has no use for Kirchhoffs law since it doesn't deal with anything physical.
The problem is that calculating all of this for a real physical circuit involving only a few components would already result in a LOT of math.
So KVL only interacts with Faradays law when circuit mesh modeling deems it necessary.
Physics has no use for Kirchhoffs law since it doesn't deal with anything physical.
Kirchhoff, one of the most important physicists of the 19th century, must be rolling over in his grave.
QuoteThe problem is that calculating all of this for a real physical circuit involving only a few components would already result in a LOT of math.
You don't get it. You have an impressive equipment on your bench all of it making extensive use of Maxwell and yet you have no clue about the theory used to design it.
In Kirchhoff's world you wouldn't have coaxial cables, ground planes, canned circuits, EMI certification, impedance matching, delay lines, coupling, decoupling, transformers, inductors, motors, generators, radiation, etc., etc., etc.
Kirchhoff is from a time when the only source of electrical energy widely available were batteries. There were no changing fields. No transients. No kind of interference. Only well-behaved DC circuits. Today, even toys using batteries have SMPSs with inductors and transformers, these specifically making use of Faraday's law.
So you can't escape Maxwell. It's everywhere these days. When we say Kirchhoff, we are in reality saying Maxwell, or Faraday in case of induction, under certain VERY special conditions. But it is still Maxwell.
Don't fool yourself or you'll end up like Cyriel Mabilde: an advocate of ignorance.
QuoteSo KVL only interacts with Faradays law when circuit mesh modeling deems it necessary.
So you're saying that on your planet the laws of Nature obey the desires of the engineer? I'm moving there right now.
KVL applies to any lumped electric circuit; it does not matter whether the circuit elements are linear, nonlinear, active, passive, time-varying, time-invariant, etc. In other words, KVL is independent of the nature of the elements.
so physics doesn't really need KVL and KCL.
Why doesn't everyone write software in a hex editor? Its the most fundamental way of doing it after all. Its just simply more practical to work on a higher level with a compiler. Yes you are missing out on some fine details with all these high level language abstractions, but in 99% of cases it doesn't matter and it does get the job done significantly faster.
I was making an example of why circuit analysis is useful in order to justify why one might want to use KVL rather than the more the accurate alternatives (the answer is deadlines).
But at least the bent laws help things calculate faster in my real world, the trick is bending them just right so that it acts almost the same as in the real world while only taking 1% of the math to get there.
So, never try anymore to hide your lack of knowledge behind excuses like that.
Abstraction and neglect of the fundamentals are orthogonal things.
Abstraction means to take away from the designer tasks and routines that are necessary but will not have any kind of influence on the result. So, if you have a menial task to do, you hand it down to a computer, or another person, or company, or the compiler, etc., so that you can concentrate on the specifics of your project. However this doesn't remove from the designer the responsibility to have full mastery of the fundamental concepts of his field.
If abstraction were the same as neglect of the fundamentals, any computer science or software engineering course will be just a class on some stupid "high level" language and nothing more.
So. You have, say, a radar to design. You have a tight deadline. You turn to your colleague and say "Bugger that! Let's use Kirchhoff and go home."
The math required for the work with Kirchhoff requires a decade or so of learning. You do not learn Kirchhoff in the first grade, do you? If the math required for Kirchhoff were so simple, you wouldn't have spice programs out there to solve them for you.
The basic math required to work with Maxwell requires less than 100 hours of study. And if the equations get really complex, you also have proper software to deal with them.
So, never try anymore to hide your lack of knowledge behind excuses like that. Convince yourself and others of the need to be ready to learn something new every day.
And this is exactly why KVL is an abstraction of Maxwells equations. It makes things easier while not influencing the result (when used correctly).
Don't worry i seen plenty of programmers that don't understand how a computer works and consider C being too low level. Some even stick to purely interpreted languages like javascript, php or python. I do think they should at least conceptually understand the inner workings of computers. Large software projects are often massive cobbled together messes with chunks of code that nobody understands why they are needed and how they work but if you touch them things break horribly so everyone stays away from them and works around them. Tight deadlines encouraging to just cobble on more rushed code until the project becomes unmaintainable. But that's a topic for another day.
Actually i was working on some phased array stuff recently and i used even more abstraction than just Kirchhoff.
I was trying to calculate the directionality of a phased array and i wanted to do it fast so that i could later use iterative optimization methods on it. I could have simulated each point in space and its interaction to the neighboring points so that i get a simulation of wave propagation trough the medium. Takes a lot of computation to do and im too lazy to program all of that. Well... instead i just did trigonometry to find the distance to each element and pretended there is an ideal delay line with its delay proportional to the distance. Worked great and it would spit out a directionality graph for all possible angles in the blink of an eye(Without even trying to optimize the code). Is this magical delay line what is actually happening on a phased array? Hell no. Does it act similar enough? For my use case plenty enough.
When the abstraction works i will definitely say "Bugger that!" to the more complicated alternatives. If the abstraction doesn't work then i will go down the long path. I don't work in an academic institution to needlessly waste time obsessing about the underlying mechanisms for cases where they are simply not important.
Well i was introduced to Kirchhoffs laws before high school. Then actually had to use them in high school to manually solve circuit meshes. Inside the circuit mesh abstraction its really easy to use.
...[snip]
I found this realization of intertwined units quite eye opening back in university. It can help you understand how non electrical things work a lot faster.
Berni, Electroboom and Cyriel Mabilde know how to measure the voltage in the demonstration circuit.
They all demonstrated it properly.
Clearly bsfeechannel and Dr Lewin don't know how to measure the voltage.
The moment you put voltmeter on as Dr Lewin did, you are measuring a scalar voltage. He did that.
But unfortunately he did it incorrectly and drew the wrong conclusion.
Maxwell-Faraday is a model the same as any other. It has limitations, and can be used successfully if it fits within them.
It is not magic. It isn't even particularly complex.
btw bsfeechannel please update your venn diagram to fix your mistake, people will get the wrong idea.
Isn't it annoying when Nature does not conform to our preconceived notions of reality?I guess it would be.
But on a brighter note we seem to agree that KVL is at lease useful for characterising transformers.
ps. I would have liked to have watched your video further but the robot voice was hurting me.
Maybe someone on EEBblog could do an English (or other language) voice over?
And this is exactly why KVL is an abstraction of Maxwells equations. It makes things easier while not influencing the result (when used correctly).
Because in many of your "abstractions" you used KVL instead of Maxwell, you think that KVL is an abstraction of Maxwell. Don't say that anymore.
Saying that means that every time you have a problem solvable by Maxwell, you can immediately apply KVL "used correctly" and that's it.
It implies that you can get away without understanding the underlying phenomena. No, you can't.
That's what Cyriel Mabilde disastrously did. That's what Lewin is desperately trying to warn you about.
Why you can get away with that in computing? Because those languages, including machine code, are all equivalent in computing power. So you can get a program working without knowing the details under the hood at the expense of a messy code.
Kirchhoff and Maxwell are NOT equivalent. If Kirchhoff and Maxwell were languages, Kirchhoff would describe a machine with LESS computing power than Maxwell.
Again. Who told you that you could reduce the problem to KVL? Kirchhoff? Certainly not. Kirchhoff is a bird. He doesn't know anything about propagation, delay lines, fields, etc.
You had to use MAXWELL, and you did it almost unconsciously, to reduce to problem to Kirchhoff. So you confirm what I said in one of my first messages on this thread about how we engineers are so used to that practice that we forget that we are in fact using Maxwell and implicitly reducing the problem to Kirchhoff.
You can abstract, but you cannot use this as an excuse to ditch the fundamentals. What people are doing is not even trying to study Maxwell, consequently not understanding what the flux is going on and criticizing Lewin for THEIR ignorance.
This is the most stupid educational move I've seen in decades.
TLDR.
Now that I've made you a convert, let's help others to avoid saying stupid things like "Physics has no use for Kirchhoffs law since it doesn't deal with anything physical."
I was almost using that quote as a signature. But then I decided to give you a second chance.
For some reason i was not allowed to insert inductors into the equivalent model and not allowed to have a voltage on a non closed loop wire segment.
Absolutely nothing wrong in that video (Okay maybe apart from the voice)
Hey, bsfeechannel, where do you come from?
You have demonstrated in the transformer video how useful the circuit mesh abstraction is. Transformers don't have additional winding that make leakage inductance, they don't have a physical resistor inside them that causes core losses. Yet it acts pretty much like that was the case so that's why the real transformer model uses it. It makes things much simpler to work with while acting close enough.
You even use such simplifications before you get to the equivalent circuit model. For example you consider two turns in a coil as simply being 2 times a single turn, while showing segments of wire that go up diagonally to connect the two and a set of wires coming out and then showing a voltage across the two wires without closing them into a loop.
For some reason i was not allowed to insert inductors into the equivalent model and not allowed to have a voltage on a non closed loop wire segment.
Absolutely nothing wrong in that video (Okay maybe apart from the voice)
If Berni, Electroboom and Cyriel Mabilde got it wrong then let us know what you think voltages are on the loop in Dr Lewins experiment.
After all these posts, you still don't get it.
you must not add extra flux into the loop
So, let me ask you again: what is 'extra flux'?
You do realize you are saying that the reading does not depends on the endpoints only but also on the path?Yes
So, you are saying Lewin is right.No
And yet, you still talk about "voltage on the loop" as if it were a property of the loop.?? I talked about measuring the voltages at A and D but only because I think that is what Dr Lewin is trying to do.
I had to make a lot of implicit assumptions to REDUCE the model. That is stated in the video. These assumptions were only possible because Maxwell told me what is going on. Kirchhoff can't explain them in any way. For instance, where does the leakage inductance come from? What exactly produces it? How can it be modeled as a lumped component? Why do we have a magnetizing current on the primary even without a load on the secondary. Is that a "parasitic" current? Can we reduce it? If we can, how? How will this affect the other parameters?
While I think about that and derive the calculations to model the device, Kirchhoff sits in the corner like Jack Horner. I only call him to the party in the last minute, when all the components of my model are figured out.
So Kirchhoff is just a fancy interface in the end to hide a complicated mechanism. It serves no purpose in the design of the transformer.
The arrow indicates where you are going to place your voltmeter, and then the loop will be closed. If the diagonal wire bothers you, just rotate the top loop clockwise a little until the connecting wire becomes perpendicular.
Because my transformer and Lewin's experiment have a crucial difference. While the transformer has a fixed topology, Lewin's experiment doesn't. And Maxwell showed that topology is everything in electromagnetism.
If you move the voltmeter an isty bitsy tiny little femtometer, it will measure a different voltage. Your voltmeter may not be sensitive enough to catch very small variations, but they will be there. There's simply no right way to measure voltages on Lewin's experiment. It is undefined.
Since Kirchhoff knows nothing about how your circuit is arranged in space, if you want to reduce Lewin's experiment to Kirchhoff you have to define the topology, either explicitly, or implicitly like in the case of a transformer, but once you do that, it will not be Lewin's experiment anymore.
For more details, revisit this post:
https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/msg1962869/#msg1962869 (https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/msg1962869/#msg1962869)
I just don't agree in his application of Kirchhoffs law to prove its wrong. It needs a lumped circuit mesh to work right
and i was able to turn his circuit into a valid and accurately behaving circuit mesh in 5 minutes where it shows that Kirchhoff indeed works.
I will get to the shortcomings of the lumped representation later, but for now, let me ask you: how did you dimension the probe's inductors? Would those values change if the probes' cables were twice as long, and covered a different area?
It's sad to hear Dr. Lewin attack Mehdi with the education jab, just so unnecessary.
Mehdi's approach and professional comments on this topic clearly show he is of the highest moral character and only wishes to constructively discuss the topic. A very well done to him.
Anxious to hear Lewin's response to the last video.
I read Belcher's paper. Nowhere he says KVL always holds or that Lewin is wrong.
We've been discussing this topic for a month now and, although apparently the vast majority of EEs on this forum understands what is at stake, there are still a few people who think that Mehdi is a hero, Lewin is a charlatan, I am a troll, and Maxwell is just a complicated version of Kirchhoff.
The problem seems to be that Lewin's "Kirchhoff is for the birds" rant is being perceived as an attack on those who learned to rely on Kirchhoff. But Lewin's rant is directed at some of those who TEACH circuit analysis.
Science validated by upvoting.
This is worrisome.
Mehdi fought the old professor and lost. But made a video to appear that he won.
When there's paper with real arguments you talk about youtube comments??
You really shall read Prof. Belcher's document
which says that Mehdi won his argument.
I promised not to interact with you on this matter, but... are you asking me where is the paper stating what I put into quotes in my previous post?
Well, it's Belcher's document.
You can not measure two different voltages when you measure in the exact same two points at the exact same point in time.
I will give it a go at explaining the problem but I'm to lazy to draw something
Well, then in case you missed that - same document states "KVL holds, as argued by Mehdi Sadaghdar"
You can not measure two different voltages when you measure in the exact same two points at the exact same point in time.
Aaaaand... we're back to square one.
You can not measure two different voltages when you measure in the exact same two points at the exact same point in time.
Aaaaand... we're back to square one.
Please point out what part of my short statement is wrong.
And if that is not wrong then what was the point of that experiment?
Please point out what part of my short statement is wrong.
And if that is not wrong then what was the point of that experiment?
I do have to agree with Sredini this time.
The problem is that this ideal voltmeter still needs wires to connect to the points of interest on the circle and that's how you can get different voltages depending on what path these wires take, they are as much part of the circuit as the loop itself.
If you take the formal definition of voltage that says that the voltage is the integral of all forces acting on electrons along a path. Then you do get a different number depending on what path do you take trough the loop. By definition there are indeed two possible voltages across the two points. This is because both the electric field of charge separation and the magnetic EMF count towards the total voltage.
Allow me to apologize for being so blunt, but I was really disappointed by Electroboom's latest video and the reaction of his fans.
The answer to your question, though, is in the many many posts of this thread. Please, browse through it and you will see that it is indeed possible for two voltmeters whose probes' tips are attached to the very same two points to read different values at the same time. There are also youtube video showing this, if you do not believe it.
The reason is in the different flux intercepted by the two meshes the circuit is partitioned into.
If you are curios, there are thirteen pages awaiting for you.
The reason is in the different flux intercepted by the two meshes the circuit is partitioned into.
Maybe if you read it again you will see that section 11 KVL is about lumped circuits. You too should go back read all past posts.
I think that regardless of absolute right or wrong Mehdi is to be commended for questioning (politely) an academic of note, creating a reasoned hypothesis of his own, testing and working through his thoughts in a practical manner on a difficult concept in a way to not turn off those not as technically minded. :-+
I think that regardless of absolute right or wrong Mehdi is to be commended for questioning (politely) an academic of note, creating a reasoned hypothesis of his own, testing and working through his thoughts in a practical manner on a difficult concept in a way to not turn off those not as technically minded. :-+
Politeness is commendable, but we are engineers. We design serious stuff: buildings, bridges, cars, airplanes, life-supporting systems, telecommunication systems, power systems.
If we give up our integrity, people die.
I think that regardless of absolute right or wrong Mehdi is to be commended for questioning (politely) an academic of note, creating a reasoned hypothesis of his own, testing and working through his thoughts in a practical manner on a difficult concept in a way to not turn off those not as technically minded. :-+
Politeness is commendable, but we are engineers. We design serious stuff: buildings, bridges, cars, airplanes, life-supporting systems, telecommunication systems, power systems.
If we give up our integrity, people die.
Not maintaining Integrity? Explain please?
I see NO where he didn't maintain his integrity at the highest level which has little or nothing being proven correct or incorrect in the long run. If English is not your first language then best you check the definition of the word. Your attacking of the mans integrity and not debating the technicalities of the subject is out of order!
Please point out what part of my short statement is wrong.
Clearly you do need a dictionary and some basic decency and manners. Attacking the integrity of the person and not the ideas as you have just done is what in Australia we would call a c... act amongst others! In particular where the person in question is not here to defend themselves. You clearly can't show where Mehdi has compromised his 'integrity'!
A quick check shows you have maybe 40 posts in this thread so clearly you have a major bee in your bonnet
and in a chunk of those posts you have decided to play the man not the subject. I will leave others to decide what this says about your character.
All the components are lumped, and we only have batteries. The real value of the voltages and resistances are not important. However, to simplify our calculations, let's suppose the two resistors have the same value (it could be any other known proportion). Connected at the same two points in the circuit we have five voltmeters.With your example, you are either claiming that both resistor values in you example are equal in value, or identical current is flowing on each side like a perfect mirror, otherwise the EMF field will be lop-sided due to the different load of the resistors.
We agree that the five voltmeters will measure exactly the same voltage.
Now let's remove the batteries and apply a magnetic field that rises linearly in intensity with time, points towards you and is confined in the total area of the circuit, i.e., A1 + A2 + A3 + A4.
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=587660;image)
According to Maxwell, this field will generate a constant EMF that will be proportional to the area enclosed by a circuit and whose polarity will be defined by the corkscrew rule. In short, the topology now counts. To simplify our calculations, let's suppose that the EMF generated by the loop enclosed by all four areas is 1V.
The voltages seen by the voltmeters will now be like that (in volts):
#1
-0.5
#2
( A1 - ( A2 + A3 + A4 ) ) / ( 2 * ( A1 + A2 + A3 + A4 ) )
#3
( ( A1 + A2 ) - ( A3 + A4 ) ) / ( 2 * ( A1 + A2 + A3 + A4 ) )
#4
( ( A1 + A2 + A3 ) - A4 ) / ( 2 * ( A1 + A2 + A3 + A4 ) )
#5
+0.5
So, what voltmeter is measuring the "correct" voltage?
With your example, you are either claiming that both resistor values in you example are equal in value, or identical current is flowing on each side like a perfect mirror, otherwise the EMF field will be lop-sided due to the different load of the resistors.
What I would like to see is having modify the original loop so that it bends inwards to the center at the measurement point, insert a tiny 6 pin sot-23 MCU right on a watch battery directly in the middle sampling the voltage at 10msps, not connection anywhere else, and optically feeding out the readings.
You're young. You need a hero. I'm old. I do not have time for this kind of nonsense.
I like to contribute. Is that a problem?
I'm not the subject of this thread. Mehdi and his (now debunked) claims are.
With your example, you are either claiming that both resistor values in you example are equal in value, or identical current is flowing on each side like a perfect mirror, otherwise the EMF field will be lop-sided due to the different load of the resistors.
What I would like to see is having modify the original loop so that it bends inwards to the center at the measurement point, insert a tiny 6 pin sot-23 MCU right on a watch battery directly in the middle sampling the voltage at 10msps, not connection anywhere else, and optically feeding out the readings.
Seriously Not young at all and yet you decide this based on what?
As to 'nonsense' you have time to attack Mehdi's integrity but not tell us where didn't maintain his integrity? Still waiting?
When you descend into criticism of the person or others here you open yourself up to becoming a subject of discussion for your behavior and personal attacks.
And Mehdi's claims are 'debunked' as decided by you?
WOW your verbosity and frequency of posting must have made it so awesome work you have me instantly convinced....
So, what voltmeter is measuring the "correct" voltage?
Each will measure a different thing but not the voltage between those two points of interest except for the one in the middle number 3 that could read the correct value of 0V assuming it was shielded since a real voltmeter will likely not be perfectly symmetrical in internal construction.
Each will measure a different thing but not the voltage between those two points of interest except for the one in the middle number 3 that could read the correct value of 0V assuming it was shielded since a real voltmeter will likely not be perfectly symmetrical in internal construction.
Excellent. So let's get rid of the other voltmeters and stick to the voltmeter #3. Let's suppose that its display has seven digits (pretty common on modern bench multimeters) and let's suppose it is properly "shielded", etc.
I hadn't defined the areas, but now let's suppose that their common side is 10cm, and that x+y = 20cm like in the picture below.
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=588280;image)
So, V3 = ( ( A1 ) - ( A2 ) ) / ( 2 * ( A1 + A2 ) ), x + y = 0.2 m and, since A1 = x * 0.1 and A2 = y * 0.1, and A1 + A2 = 0.02m², we will have that V3 in volts:
V3 = ( ( x * .1 ) - ( y * .1) ) / ( 0.04 ) = ( x - y)/0.4
If x = y, then V3 should read 0.000000V.
But now, let's imagine for a moment that this circuit doesn't have the voltmeter and then suddenly someone decides to connect it.
Look what happens if the unfortunate engineer assigned with that task misses the exact point of connection and places the voltmeter 200nm to the right. 200 nanometers. In that case x = 0.1000002 m, and y = 0.0999998 m.
V3 = (0.1000002 - 0.0999998) / 0.4 = 0.000001 V
So it's affecting the precision of the measurement. It's no biggie in this case because we know what to expect ( 0V). But what if the resistors didn't have exactly the same value? How do I know that this error is not due to a resistor mismatch? Because I could nanometrically place the voltmeter in the "correct" spot, adjusting it so that its voltage read the expected 0.000000V. But what if a mismatch in the value of the resistors is giving me a false reading?
Yes according to the math there are two voltages across A and B, but this is not a voltage that can be used for anything until wires are run to it to connect it to something(Such as a voltmeter). Once that is done the path is defined completely and the resulting voltage is only a single well defined voltage appearing across the voltmeter you connected it to. What sort of EMF the voltmeters wires experience is totally up to you, but usually its most usefully that there is zero EMF because you can then consider the wire as being an ideal connection between two circuit nodes.
Yes according to the math there are two voltages across A and B, but this is not a voltage that can be used for anything until wires are run to it to connect it to something(Such as a voltmeter). Once that is done the path is defined completely and the resulting voltage is only a single well defined voltage appearing across the voltmeter you connected it to. What sort of EMF the voltmeters wires experience is totally up to you, but usually its most usefully that there is zero EMF because you can then consider the wire as being an ideal connection between two circuit nodes.
What is the math for the above example and what will those two different voltages be ? -0V and +0V :)
From my understanding of physics in this universe (going to assume there is no parallel universe with same experiment running at the exact same time) there will always be a single voltage between any two points at a fixed moment in time no mater if there is a measurement device in there or not.
This is the reason why its so confusing.
This is the reason why its so confusing.
First of all this is not a weird quantum mechanics thing like Schrodingers cat thought experiment that the cat is both dead and alive simultaneously until you look at it. Instead it is actually the fault of how voltage is defined in textbooks.
The more common way of thinking about voltage is that more electrons there are in one place the more negative that point is, connect this area with lots of electrons to an area with few electrons and you get current between them as the charges want to even out.
The way voltage is actually formally defined is "An integral of all forces working on charges along a path between two points". These forces include the electric field that bunched together electrons create, but it also includes the magnetic forces pushing electrons around (Any charged particle is affected by a changing magnetic field). This force is dependan't on where you are in the magnetic field. This results in a different result of the integral of the force and hence a different voltage.
In Dr. Lewins example you get the magnetic EMF adding to the resistors voltage if you go around one way, but subtracting from the resistors voltage if you go around the other way. Hence the integral is different and there is different voltage. Its just how the math ends up working out. The actual electron charge density at the points A and B is always a single well defined number. The voltage you measure by connecting a voltmeter as you shown will measure this electron density. Hence why the voltmeter shows one voltage.
The two different voltages result from Dr. Lewins example could be sort of a incomplete result of the voltage so far, you need to include the rest of the circuit to properly define the voltage. Think of the two voltages as sort of like complex number math, they don't necessarily exist in the real world but they make the math work.
I do not disagree with anything you mentioned in you last replay. Correct measurement will read a single value and that is the real 0V no multiple voltages at a single defined point in time.
Of course if you move the measurement point you get a different reading that is normal in any circuit not just this particular case.
I don't know if someone has previously posted this link. Its worth watching.
Ah okay you want to know the voltages. Given that the total EMF is 1V the result is -0.5V on one side and + 0.5V on the other side. This is because wires show up as having no voltage while the resistors show a voltage according to Ohms law. Since the current trough the loop is identical everywhere this means both resistors have to show the same drop (given they are the same value). Sine the current is flowing upwards in one resistor and down the other you get opposite voltage polarity. So you do get two voltages.You can only read -0.5V and +0.5V if you cut the circuit in half on those two measurement points and then measure each of the half circuits but then that is a completely different circuit and it is no different from a circuit where you have batteries. A real battery has the internal impedance distributed trough the battery is not like there is an ideal source inside and then a separate impedance as it is represented in a diagram.
Well, in case of the first circuit supplied by batteries with no varying magnetic flux, you agreed with me that all five voltmeters would read the same, i.e. the real position of the voltmeters didn't matter. But let's forget that for the moment.
Because I agree with you that in this particular case, any misplacement of the voltmeter will reflect on the precision of the measuring.
But my question remains unanswered.
How do I know that this imprecision is due to the voltmeter not being exactly in the place it should be, and not due to a resistor mismatch?
You know, resistors change their values, either with temperature, or age, or both, etc.
My examples where meant to get rid of the confusion of having wires and separate resistors but any example will work the same.
[...]
You can use KVL to find out voltage between any two points on those example rings.
Not sure what sort of point you want to make.
The discussion here is that there is only one voltage between the two defined points at a fixed moment in time and that KVL applied correctly will give you the correct result.
Of course real circuits are not perfect and that is why you have tolerances but you add those tolerances in your calculation and your result will have a margin of error proportional with those tolerances.
Ok, let's take a loop made of two big resistors - physically big - and some copper wire. Let's say the resistors are shaped into an arc spanning 45 degrees. One is 0.1 ohm, the other one is 0.9 ohm. Emf in the loop is 1V.
What is the real and only voltage across the resistors?
What is the real and only voltage across the remaining two portions of wire (say it's copper)?
But all you did was split the ring in to 4 equal parts
and have 4 resistors two with equal low resistance (the copper wires) and the other two with higher resistance 0.1Ohm and 0.9Ohm
you will measure say +650mV across the 0.9Ohm resistor and then -150mV across the 0.1Ohm resistor
But all you did was split the ring in to 4 equal parts
Not equal (360 - 2x45 = 270; 270/2 = 135 != 45), but that's immaterial.Quoteand have 4 resistors two with equal low resistance (the copper wires) and the other two with higher resistance 0.1Ohm and 0.9Ohm
Correct. So, let's make the resistors span 90 degrees instead of 45 so we can use your numbers.Quoteyou will measure say +650mV across the 0.9Ohm resistor and then -150mV across the 0.1Ohm resistor
The only and true voltage across the 0.9 ohm resistor is .65 V. Ohm would say there's a current of .65/.9 = .72 amps
The only and true voltage across the 0.1 ohm resistor is .15 V. Ohm would say there's a current of .15/.1 = 1.5 amps
Now, .65 + .15 = .80 V. EMF is 1V, I suppose you want to put that into 'modified KVL', so did you bungle the calculation or are you assuming there are 0.20 voltage drop on the copper wires? If we assume 0 resistance that would mean ohm would think there's infinite current.
But let's leave ohm alone for the moment because you might want to put some EMF here and there.
Can you put KVL into a formula with numbers? Please make the (possibly corrected, if required) numbers of all the 'true' voltage drops in the loop and show that KVL balance.
Mehdi posted a follow-up video:
The formula is very simple each quarter of the ring (90 degree) will see a quarter of that 1V so 0.25V
Thus depending on the direction of the current you have +0.9V across the 0.9Ohm resistor but you subtract 0.25V thus +650mV
On the other side of the ring (again my assumption the other resistor is on the other half) you have 0.1V on the resistor and subtract 0.25V so -150mV
The copper wires are treated the same as the resistors so a 0.25V source and whatever resistance those wires have say is 1mOhm for each quarter segment in series
If you disagree with this please provide your numbers and how you got to them.
I do not believe in a 'true' voltage (actually it's not a belief, the formulas tell me). In this case it all depends on how you measure it - I can get your numbers by suitably partitioning the disk with the probes, or many other values. But I tell you how I can balance Faraday here:
EMF = 1V, total loop resistance 1 ohm, current 1 amp
integral of E dl in 0.9 ohm + integral of E dl in 0.1 ohm + nearly nothing in copper = EMF
0.9 + 0.1 + 0 = 1
In your case, well, what is the field inside the copper parts, if you have 0.25 V across each of them?
QuoteIf you disagree with this please provide your numbers and how you got to them.
I do not believe in a 'true' voltage (actually it's not a belief, the formulas tell me). In this case it all depends on how you measure it - I can get your numbers by suitably partitioning the disk with the probes, or many other values. But I tell you how I can balance Faraday here:
EMF = 1V, total loop resistance 1 ohm, current 1 amp
integral of E dl in 0.9 ohm + integral of E dl in 0.1 ohm + nearly nothing in copper = EMF
0.9 + 0.1 + 0 = 1
(signs come about when you consider the correct conventions)
My ohm's law still work. I had to give up uniqueness of voltage between two points, though.
Most importantly, there is practically no field inside the copper conductor, as predicted by Maxwell's equations.
In your case, well, what is the field inside the copper parts, if you have 0.25 V across each of them?
If superconductive, then E field is 0.0V. In this case it is 0.002 V because wire is specified as 0.001 Ohms per segment.
[edit] We don't measure E field or EMF between two points of the circuit. We usually measure potential difference.
So are you saying that voltage across the 0.9Ohm resistor in the current example is 0.9V ?If I measure from outside, and without crossing the flux varying region, yes.
because that sure is not the case unless the resistor has an infinitely small size
If superconductive, then E field is 0.0V. In this case it is 0.002 V because wire is specified as 0.001 Ohms per segment.
[edit] We don't measure E field or EMF between two points of the circuit. We usually measure potential difference.
Thanks I'm worse on expressing myself :) so your replay is shorter and more to the point.
I'd like to kindly ask the Kirchhoff experts what tools do Kirchhoff rules give me to calculate the "right" voltage of the loop below. Except for the irregular perimeter, all conditions are the same as for my rectangular loop above.
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=589078;image)
I need to know the exact points where to connect the voltmeter and its precise location. Any reply will be appreciated.
So, you measure electric field in volts?
You need to brush up on basic physics.
Please, humor me and try again: what is the field inside the copper conductor and how do you justify - with formulas - that there is a 0.25 volts drop across it?
So are you saying that voltage across the 0.9Ohm resistor in the current example is 0.9V ?If I measure from outside, and without crossing the flux varying region, yes.
Note that I did not use 'voltage drop' but the integral of E.dl in my balance.
I sort of feel like I deal with trolls
So, you measure electric field in volts?
You need to brush up on basic physics.
I did not mention any units at all. You need to check your vision.
I sort of feel like I deal with trolls and I hope that is not the case.
Have you discovered magnetic monopoles?
I am asking for the electric field E inside the conductor - to be more precise, the tangential component that contribute to the integral of E.dl .
I can tell you that in my case it would be in the mV/m range.
What value do you get in your case?
What are you afraid of? If your claims are sound, you would instantly know the answer for the questions we've posed. Even for the one Sredni found amusing. If you think that that question is out of proportion, think again. That could very well be traces on a PCB or wires on any real installation. If your Kirchhoff only works for perfectly rectangular or round loops, with known resistors within tolerances, it is a useless theory.
I am asking for the electric field E inside the conductor - to be more precise, the tangential component that contribute to the integral of E.dl .
I can tell you that in my case it would be in the mV/m range.
What value do you get in your case?
OK I think I understand what part you do not understand so I will try to find a bit of a different example
Can you or can you not compute this electric field?This tread is here to discuss about the silly idea that you can read two different voltages measured between the exact same two points at the exact same moment in time.
Our circuit is stationary, nothing is moving.
What is the electric field inside your conductor?
You are not telling because you do not know how to compute it, or because you cannot justify a 0.25 V (yeah, minus 0.002V) voltage difference at its ends?
Because that's the point.
Yes that generator example is spot on.
The last two pages of arguing in this thread seam to be all because of different definitions of voltage.
The correct formal definition used by Dr Lewin: Voltage is the integral of all forces on charges along a given path
The common definition used in circuit analysis: Voltage is the difference in charge density between two points
[...]
So I suggest that you make it clear in further discussion what kind of voltage you are talking about.
I sort of feel like I deal with trolls
Me too. What a coincidence :-DD
You agreed with ogden, who expressed electric field in volts. You should have read better, before saying that his reply was more to the point.
What is the field inside the copper conductor and how do you justify - with formulas - that there is a (0.25-0.002) volts difference across it?
Assume standard conductivity for copper, say 5.8 10^7 mhos per meter
Ok.QuoteWhat is the field inside the copper conductor and how do you justify - with formulas - that there is a (0.25-0.002) volts difference across it?BTW wire fragment resistance is 0.001 Ohms so it is (0.25-0.001) Volts, not (0.25-0.002).
Inside our conductor there are two E fields: E.induced and E.coloumb. Total electric field E = E.coloumb + E.induced. Coulomb electric field in the wire is opposite the direction of the induced electric field
- that's the justification of voltage difference.
Potential difference (integral of E.dl) at the ends of that copper conductor you calculate using same formula as for 0.25V chemical battery that has 0.001 Ohm internal resistance and 1A current load. Answer is mentioned already here in this thread.Please, indulge me. Give me the number in V/m (volts per meter).
I am looking forward to seeing how you compute the field and how well it fits with the 0.25-0.001 volts difference at the extremes.QuoteAssume standard conductivity for copper, say 5.8 10^7 mhos per meterDo not introduce new unnecessary conditions.
Yes that generator example is spot on.
The last two pages of arguing in this thread seam to be all because of different definitions of voltage.
The correct formal definition used by Dr Lewin: Voltage is the integral of all forces on charges along a given path
The common definition used in circuit analysis: Voltage is the difference in charge density between two points
[...]
So I suggest that you make it clear in further discussion what kind of voltage you are talking about.
Just out of curiosity...
Have you ever heard the term "dimensional analysis"?
(Also, I guess you won't tell us what the field inside the conductor is... Kirchhoffians are allergic to electric fields, it appears)
I am not sure I can sort this mess.
I'd like to kindly ask the Kirchhoff experts what tools do Kirchhoff rules give me to calculate the "right" voltage of the loop below. Except for the irregular perimeter, all conditions are the same as for my rectangular loop above.
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=589078;image)
I need to know the exact points where to connect the voltmeter and its precise location. Any reply will be appreciated.
The field inside the copper conductor is the sum of E.coloumb with E.induced, you said (and I agree). How do you think the copper can tell which is which?
The copper sees the net, resulting, field. (and THIS is the point)
What is this sum?
QuotePotential difference (integral of E.dl) at the ends of that copper conductor you calculate using same formula as for 0.25V chemical battery that has 0.001 Ohm internal resistance and 1A current load. Answer is mentioned already here in this thread.Please, indulge me. Give me the number in V/m (volts per meter).
Oh and also i solved your curvy wire example.
Here is where you have to put the voltmeter for it to read 0V
Solved using Solidworks Fusion 360 due to it having a convenient area measurement tool.
I sort of feel like I deal with trolls
Me too. What a coincidence :-DD
More like my probing technique is bigger in 'theory' than yours ;)
Far to much theoretical waffle and going around in circles or in some cases non circular circuits. Given this is a forum for EE's not theoretical Physicists with very average probing technique, get on design the experiment, test it and prove or disprove it and then get it repeated by others.
Oh and also i solved your curvy wire example.
Here is where you have to put the voltmeter for it to read 0V
Solved using Solidworks Fusion 360 due to it having a convenient area measurement tool.
Wonderful. Much appreciated. Now we need to measure the voltage indicated by the calculations so as to confirm that they are right. But, alas, in the real circuit there is a physical obstruction, that in no way affects the magnetic field. This obstruction goes all the way with the field while it is perpendicular to the surface.
How can we measure measure that voltage? Thanks in advance for your kind reply.
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=589588;image)
Wonderful. Much appreciated. Now we need to measure the voltage indicated by the calculations so as to confirm that they are right. But, alas, in the real circuit there is a physical obstruction, that in no way affects the magnetic field. This obstruction goes all the way with the field while it is perpendicular to the surface.
How can we measure measure that voltage? Thanks in advance for your kind reply.
Does Ohm's Law still work? I've got this LED I have to turn on and I need to know which side of the LED to put the resistor...
The field inside the copper conductor is the sum of E.coloumb with E.induced, you said (and I agree). How do you think the copper can tell which is which?What are you smoking?
Integral of E.dl where E = E.coloumb + E.induced. EMF of wire segment is EMF.total/4 (because segment is 1/4 of loop) = 1/4V and voltage drop due to current is 0.001Ohm*1A = 0.001V. So, this sum is 0.25+(-0.001) Volts. What's the point to ask question so many times?
Please, indulge me. Give me the number in V/m (volts per meter).Quote from: ogden:-// With same success you can ask me weight of the wire used in experiment. Before asking V/m, make sure you give enough data to calculate such (https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/msg2016091/#msg2016091) :palm:
So, let me ask you again, because this is important:
What is the field inside the copper conductor and how do you justify - with formulas - that there is a (0.25-0.002) volts difference across it?
Assume standard conductivity for copper, say 5.8 10^7 mhos per meter and a copper section of 1 mm in diameter (or any real world value you can attribute to a circuit similar to those shown by Lewin, Mehdi or Mabilde - it's about 10 cm diameter loop, suppose half of it is allocated by the big resistors, but it's not important).
I am asking for the electric field E inside the conductor - to be more precise, the tangential component that contribute to the integral of E.dl .
I can tell you that in my case it would be in the mV/m range.
What value do you get in your case?
Quote from: ogdenIntegral of E.dl where E = E.coloumb + E.induced. EMF of wire segment is EMF.total/4 (because segment is 1/4 of loop) = 1/4V and voltage drop due to current is 0.001Ohm*1A = 0.001V. So, this sum is 0.25+(-0.001) Volts. What's the point to ask question so many times?Because you guys keep telling me the voltage. I want to know the electric field.
Quote from: SredniAssume standard conductivity for copper, say 5.8 10^7 mhos per meter and a copper section of 1 mm in diameter (or any real world value you can attribute to a circuit similar to those shown by Lewin, Mehdi or Mabilde - it's about 10 cm diameter loop, suppose half of it is allocated by the big resistors, but it's not important).
I am asking for the electric field E inside the conductor - to be more precise, the tangential component that contribute to the integral of E.dl .
I can tell you that in my case it would be in the mV/m range.
What value do you get in your case?
And still, no answer.
Because you guys keep telling me the voltage. I want to know the electric field.I said (E = E.coloumb + E.induced). Are you satisfied now?
You can either provide solution yourself and tell what you want to say with it or stick that tangential component where it hurts. I do not see the point of solving your tasks. "Trail of the troll" was at least funny.
Does Ohm's Law still work? I've got this LED I have to turn on and I need to know which side of the LED to put the resistor...
Does Ohm's Law still work? I've got this LED I have to turn on and I need to know which side of the LED to put the resistor...
This question is actually a lot more relevant than it appears here (due to its ironic nature),
Ok, you have no idea on how to compute the electric field inside a conductor. It's not a crime. Maybe all that facepalming has interfered with your mental processes but, fine.
Any other Kirchhoffian who believes that the 'real' voltage across the 0.9 ohm resistor is 0.65 V and the real voltage across one of the two arcs of copper is 0.25-0.001 V care to tell us what the electric field is inside said copper?
Does Ohm's Law still work? I've got this LED I have to turn on and I need to know which side of the LED to put the resistor...
This question is actually a lot more relevant than it appears here (due to its ironic nature), as the basic Ohm's law links voltage, resistance and current. Now what is voltage again? ;D
Incidentally, Kirchhoff (not him again!) reformulated Ohm's law as: J = sigma.E
So, may be on to something.
Ok, you have no idea on how to compute the electric field inside a conductor. It's not a crime. Maybe all that facepalming has interfered with your mental processes but, fine.
Any other Kirchhoffian who believes that the 'real' voltage across the 0.9 ohm resistor is 0.65 V and the real voltage across one of the two arcs of copper is 0.25-0.001 V care to tell us what the electric field is inside said copper?
Yes, I have to dig into it to solve it. So what. Original Dr.Lewins experiment assumed that conductors have no resistance, so no coloumb E-field.
Now you are modifying it to prove what exactly?- That your debate opponents cannot calculate something during time they are willing to spend, so this is proof that you are right? BTW this is typical tactic of internet trolls - derail discussion into personal attacks.
Better tell your E-field number and make your point. Educate Kirchoff believers, don't let them compute what you can do in a snap.
Ok, you have no idea on how to compute the electric field inside a conductor. It's not a crime. Maybe all that facepalming has interfered with your mental processes but, fine.
Any other Kirchhoffian who believes that the 'real' voltage across the 0.9 ohm resistor is 0.65 V and the real voltage across one of the two arcs of copper is 0.25-0.001 V care to tell us what the electric field is inside said copper?
Have you read my replay with the servo motor or transformer experiment.
Please do that experiment as there your measurement device will be outside of the changing magnetic field and so you will get the correct result.
Also, I already told what my aim is in one of my previous post: to show that since there could not be a significant electric field inside the copper (it is zero in a perfect conductor) it is nonsense thinking that you can still have an induced field capable of producing a 0.25V voltage at the extremes
The induced E field inside the conductor is compensated by the field caused by redistribution of charge.
Also, I already told what my aim is in one of my previous post: to show that since there could not be a significant electric field inside the copper (it is zero in a perfect conductor) it is nonsense thinking that you can still have an induced field capable of producing a 0.25V voltage at the extremes
Wait... What you just said? - That in ideal conductor can't be EMF (induced field)? I am speechless to be honest. We are back to square one where you stop posting and go watch videos of Dr.Lewin. He is brilliant teacher BTW.QuoteThe induced E field inside the conductor is compensated by the field caused by redistribution of charge.
This is exactly what I was telling multiple times already, E = E.coloumb + E.induced.
Also, I already told what my aim is in one of my previous post: to show that since there could not be a significant electric field inside the copper (it is zero in a perfect conductor) it is nonsense thinking that you can still have an induced field capable of producing a 0.25V voltage at the extremes
Wait... What you just said? - That in ideal conductor can't be EMF (induced field)?
No, I said that in a perfect conductor there cannot be a non-zero resultant E field. While in copper you get a small field compatible with j = sigma E.
And still you can't see.
What is E, then?
Also, I already told what my aim is in one of my previous post: to show that since there could not be a significant electric field inside the copper (it is zero in a perfect conductor) it is nonsense thinking that you can still have an induced field capable of producing a 0.25V voltage at the extremes
Wait... What you just said? - That in ideal conductor can't be EMF (induced field)?
No, I said that in a perfect conductor there cannot be a non-zero resultant E field. While in copper you get a small field compatible with j = sigma E.
This is not what you said. You correctly say that E.coloumb in ideal conductor is zero, then you imply that it means that it is nonsense to have 0.25V induced field (EMF). Read your own words for god's sake: "since there could not be a significant electric field inside the copper (it is zero in a perfect conductor) it is nonsense thinking that you can still have an induced field capable of producing a 0.25V voltage at the extremes".
E is sum of two fields, E.induced + E.coloumb - you can do the math and calculate (do integral over E.dl) potential difference at the ends of wire segment that is subject to both E-fields. This part is explained by Lewin himself BTW.
Do you still think that inside the copper there will be the same induced field?
if you think that you can still have your unaltered induced field inside the copper you are thinking nonsense.
So, after all this posts you still have to answer what is the value of the resulting E field in V/m in copper.
So, after all this posts you still have to answer what is the value of the resulting E field in V/m in copper.
By the choice of your words you sense that there is probably something wrong with your "probing technique". It's not sponsored by any electronics engineering fundamentals which pretty much describes tried and true experimental phenomena along the past two centuries up to this day. You only rely on a couple of 10 min or so videos on the internet without even questioning their content. Any serious trade like ours upon which the lives of people depend deserves a little more rigor.
There is no real rigor left in this thread
There is no real rigor left in this thread
What kind of rigor can you expect from people who wriggle like eels and refuse to compute the field in their circuit?
I have seen lots and lots of words to go around that simple question. And the reason is that they will end up with inconsistent results.
They believe they can have .25 V across a piece of copper 7cm long, 1mm diameter with nearly zero field inside. Or non-negligible field (much much higher than that allowed by the constitutive equation) inside a good conductor. What rigor can you expect?
This is why Lewin stopped answering questions about this matter. Flat-earthers always come up with new excuses, no matter what.
Now there is 'apparent electric field'.
Flat-earthers always come up with new excuses, no matter what.
When they are out of arguments in existing discussion, they invent new useless challenges - just like you.
A challenge is what distinguishes a professional from a wannabe. The versed from the amateur. The authentic from the impostor.
Quote from: BerniYes i noticed the two being thrown into the same basket and considered as one thing all too often in this thread.
Yes, and you should ask yourself why.QuoteThe real electric field caused by charge separated electrons is a different thing that the apparent electric field that the electrons feel due to the magnetic interaction with them. The two have very different underlying mechanisms behind them.
Do you think the copper can tell the difference?
Or will it just experience the superposition of both fields?
I gave up my hopes on ogden, but you might make it.
Here's a hint, from electrostatics.
The field produced from a point charge is radially directed and goes as 1/r^2.
Now put a piece of copper near it.
Will the field inside the piece of copper be still radially directed from the source?
Or maybe, the free charges in the conductor will distribuite themselves in such a way to compensate for that radial field, so that the resulting field will be zero inside the conductor?
Does it matter the underlying mechanism that produced the various contributions to the total field?
Where is it written that superposition of electric fields only works for... 'same mechanism origin' fields only?
That's just an engineering problem at this point.
1) Make a length of wire that would fit across those two points as if the pesky barrier was not there
2) Make a rigid wire structure that goes around the barrier as needed and connects to a voltmeter on the other end
3) Make another copy of the structure from 2, but short it using the piece of wire from 1
4) Place the structure from 2 onto the circuit to tap the voltage and place the structure from 3 anywhere near by
5) Subtract the readings of the voltmeters.
The compensation structure from 3 can be used multiple times to ensure the field is indeed uniform all around so that we know the placement of the structure has shown valid readings.
Alternatives are to just calculate the voltage of the compensation structure if you already know the exact properties of the field, or in that case if you know the properties of the field and the path of the wire you want to measure you can just apply Faradays law to the whole thing.
Remember im not trying to disprove anything about Faraday or Maxwell. Just saying that Kirchhoffs laws are convenient to use in some cases (And they do work when used correctly).
LOL. Who would say so. BTW you also came with useless challenge. Now both of you can challenge each other until it hurts. This thread became :horse: - like both of you wanted.
LOL. Who would say so. BTW you also came with useless challenge. Now both of you can challenge each other until it hurts. This thread became :horse: - like both of you wanted.
I told you: go get yourself a better education. Now you can see that praising Mehdi and Mabilde and bashing Lewin didn't get you smarter.
Next time, listen to the voice of experience.
LOL. Who would say so. BTW you also came with useless challenge. Now both of you can challenge each other until it hurts. This thread became :horse: - like both of you wanted.
I told you: go get yourself a better education. Now you can see that praising Mehdi and Mabilde and bashing Lewin didn't get you smarter.
Next time, listen to the voice of experience.
Being a loudmouth (or loud typist) and attempting to belittle others is not educational or helpful to a debate it is no more than behaving like a petty bully in the schoolyard. But as you claim to be an adult with the ability to read this may be of benefit but I doubt you would understand it. https://www.psychologytoday.com/au/blog/neurosagacity/201702/how-tell-youre-dealing-malignant-narcissist (https://www.psychologytoday.com/au/blog/neurosagacity/201702/how-tell-youre-dealing-malignant-narcissist)
But why did you quote Bsfeechannel exasperation post to tell him that? ;D
And this is why it is nonsense to believe that you can locate a field big enough to give 0.25V voltage (integral of E.dl along the conductor) in the copper parts of the loop.
You would break the constitutive equation in copper. You would count twice the effects of the induced field.
Not even close to funny.
You asked several times about the size of the loop and I probably mentioned that is irrelevant for the problem
It wasn't meant to be funny. It was a sarcastic grin.
I suggest you go back reading ogden's posts in this thread and revise your judgment. All he did was to facepalm, LOL, belittle and tell other people they were trolls, to stick it where it hurts and so on.
But no, we should put up with that shit and give him an award for just showing up and saying bullshit.
Sorry, not all posters in this forum align to the politically correctness craze that is so endemic to the US.
I tried not to respond to provocations, but to fault bsfeechannel for telling him to go study, is in my eye a bit excessive.
He is the incarnation of the people who do not know, but think they know Lewin was talking about.
Enough is enough.
It wasn't meant to be funny. It was a sarcastic grin.
I suggest you go back reading ogden's posts in this thread and revise your judgment. All he did was to facepalm, LOL, belittle and tell other people they were trolls, to stick it where it hurts and so on.
But no, we should put up with that shit and give him an award for just showing up and saying bullshit.
Sorry, not all posters in this forum align to the politically correctness craze that is so endemic to the US.
I tried not to respond to provocations, but to fault bsfeechannel for telling him to go study, is in my eye a bit excessive.
He is the incarnation of the people who do not know, but think they know Lewin was talking about.
Enough is enough.
Nowhere have I defended any of you including Ogden that have resorted to name calling and petty or even malicious taunts. This has nothing to do with political correctness so don't use that as an excuse to continue disrespectful conduct! Do you behave like this professionally or just here behind a keyboard?
Stick to the subject and there may be hope!
Physical size is relevant to get the E field and current density j values.
I am beginning to suspect you think those are mytical quantities. Like unicorns.
I'll try to be more specific: if I know the current and I want to find the current density, I have to divide by the area of the wire's section. Also, voltage along a path is the integral of the electric field, do you think that knowing how long the path you are integrating on can have some relevance?
That's just an engineering problem at this point.
1) Make a length of wire that would fit across those two points as if the pesky barrier was not there
2) Make a rigid wire structure that goes around the barrier as needed and connects to a voltmeter on the other end
3) Make another copy of the structure from 2, but short it using the piece of wire from 1
4) Place the structure from 2 onto the circuit to tap the voltage and place the structure from 3 anywhere near by
5) Subtract the readings of the voltmeters.
The compensation structure from 3 can be used multiple times to ensure the field is indeed uniform all around so that we know the placement of the structure has shown valid readings.
Alternatives are to just calculate the voltage of the compensation structure if you already know the exact properties of the field, or in that case if you know the properties of the field and the path of the wire you want to measure you can just apply Faradays law to the whole thing.
Remember im not trying to disprove anything about Faraday or Maxwell. Just saying that Kirchhoffs laws are convenient to use in some cases (And they do work when used correctly).
After trying to follow your instructions, I am not sure if I understand what you mean without a drawing. So I decided to simplify the challenge. Let's suppose that the whole internal area of the loop is completely occupied by the obstruction.
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=590755;image)
Perhaps that way it becomes easier for me to understand.
Tho a lot of this thread has seam to have devolved into insults
Same procedure still works, just needs longer probe wires to get around the larger obstruction.
Tho a lot of this thread has seam to have devolved into insults (Nothing towards me but towards others) rather than creative discussion so il probably stop participating in it if this continues.
From very beginning "Kirchoff for the birds" fans arrogantly insulted nearly everybody who disagree with them.
I'm afraid of you being a troll and wasting my time.
Read the replay above as it may be relevant if you are not a troll.
Shape of the loop will make no difference as long as B-flux is uniform but if that is not the case then you will not be able to calculate that with just pen and paper (you may be able to approximate something) but you will need a computer simulation tool to solve that and of course all details to scale.
And even if flux is uniform you will need to know the total length of that loop and the length between the two points you want to make the measurement then calculation is the same as for the simple ring model as shape alone makes no difference.
So how does a voltmeter tell the difference if it only shows the field caused by electron density and not the magnetic EMF? (Hint: It does show some EMF too but not where you would typically want)
If voltmeters treat the two separately, why should we treat them as the same thing? We are trying to calculate what the voltmeter would show after all.
I'm not trying to pick sides here, or say anything negative about anyone. To me it seams that most people in this thread are not saying anything wrong for the most part, but the disagreement seams to stem from using a slightly different definition of things and more rarely a bit from just having a different thought process about this thing.
If you integrate E dot dl through an unbiased diode, you get a voltage! Diodes violate KVL!
If you integrate E dot dl through an unbiased diode, you get a voltage! Diodes violate KVL!
Indeed. Chemical battery violates KVL as well. Resistor and any other lone component violates KVL. Kirchoff's Circuit Laws requires closed Circuit.
You can make a closed circuit by connecting the diode leads together with a wire. Go around the loop and calculate the integral of E dot dl.
When we agree that 1/4 of the Dr.Lewin's experiment (inner) loop receives EMF/4 and can be treated as lumped element meaning Berni model (https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/msg1945312/#msg1945312) is correct - then there's ground for conversation.
Take the example of a PN junction diode. It clearly has different electron densities in the P and N depletion region. There is an electrostatic potential difference due to the charge separation. But a voltmeter measures zero volts when connected to the leads of the diode.
Take the example of a PN junction diode. It clearly has different electron densities in the P and N depletion region. There is an electrostatic potential difference due to the charge separation. But a voltmeter measures zero volts when connected to the leads of the diode.
The reason for that is that to connect to the silicon you have to create ohmic contacts (non-rectifying contacts) and...
Nah, I'll use the first link.
https://www.quora.com/Why-we-cant-measure-the-barrier-potential-existing-across-a-p-n-junction-by-connecting-voltmeter-across-the-p-n-junction (https://www.quora.com/Why-we-cant-measure-the-barrier-potential-existing-across-a-p-n-junction-by-connecting-voltmeter-across-the-p-n-junction)
Sometimes it is said that electric currents are driven by differences in electrostatic potential (Galvani potential), but this is not exactly true.[2] As a counterexample, multi-material devices such as p–n junctions contain internal electrostatic potential differences at equilibrium, yet without any accompanying net current; if a voltmeter is attached to the junction, one simply measures zero volts.[3] Clearly, the electrostatic potential is not the only factor influencing the flow of charge in a material—Pauli repulsion, carrier concentration gradients, electromagnetic induction, and thermal effects also play an important role.
In fact, the quantity called voltage as measured in an electronic circuit has a simple relationship to the chemical potential for electrons (Fermi level). When the leads of a voltmeter are attached to two points in a circuit, the displayed voltage is a measure of the total work transferred when a unit charge is allowed to move from one point to the other. If a simple wire is connected between two points of differing voltage (forming a short circuit), current will flow from positive to negative voltage, converting the available work into heat...
The reason for that is that to connect to the silicon you have to create ohmic contacts (non-rectifying contacts) and...Don't believe everything you read on the internet.
Nah, I'll use the first link.
https://www.quora.com/Why-we-cant-measure-the-barrier-potential-existing-across-a-p-n-junction-by-connecting-voltmeter-across-the-p-n-junction (https://www.quora.com/Why-we-cant-measure-the-barrier-potential-existing-across-a-p-n-junction-by-connecting-voltmeter-across-the-p-n-junction)
The voltmeter reads the difference in Fermi levels between the two contacts:
https://en.wikipedia.org/wiki/Fermi_level (https://en.wikipedia.org/wiki/Fermi_level)
With no bias, in equilibrium, the Fermi levels on both terminals are equal, so zero voltage. Refer to figure 7.3 of Neamen.The reason for that is that to connect to the silicon you have to create ohmic contacts (non-rectifying contacts) and...Don't believe everything you read on the internet.
Nah, I'll use the first link.
https://www.quora.com/Why-we-cant-measure-the-barrier-potential-existing-across-a-p-n-junction-by-connecting-voltmeter-across-the-p-n-junction (https://www.quora.com/Why-we-cant-measure-the-barrier-potential-existing-across-a-p-n-junction-by-connecting-voltmeter-across-the-p-n-junction)
The voltmeter reads the difference in Fermi levels between the two contacts:
https://en.wikipedia.org/wiki/Fermi_level (https://en.wikipedia.org/wiki/Fermi_level)
Well, wikipedia is on the Internet, so I shouldn't believe it. But maybe you misquoted it.
Besides, the difference in Fermi levels is the barrier potential (if we agree on how to treat the sign). I guess you were the one saying that you cannot read it with a voltmeter.
You have to wonder if "potential barrier" is the right phrase for an ohmic contact, which should have little or no barrier.
But if you want a reference that is not on the Internet, you might want to read page 242 of "Semiconductor Physics and Devices" by Donald Neamen.
"This potential difference across the junction cannot be measured with a voltmeter because new potential barriers will be formed between the probes and the semiconductor that will cancel V_bi"
This is the first book I took off my shelf, but I'm pretty sure I could find something along the same line on Sze, or on Streetman, or on Muller Kamins.So what's your point? Are you saying that there is no net electrostatic potential across the diode terminals?
Oh my.
"This potential difference across the junction cannot be measured with a voltmeter because new potential barriers will be formed between the probes and the semiconductor that will cancel V_bi"
So what's your point?
I'm not clear what you are talking about. So the two voltmeters in this experiment are not affected by the EMF? Then why do they read different voltages?
Anyway, voltmeters don't read the field caused by electron density. They don't read the electrostatic potential. Take the example of a PN junction diode. It clearly has different electron densities in the P and N depletion region. There is an electrostatic potential difference due to the charge separation. But a voltmeter measures zero volts when connected to the leads of the diode.
If you integrate E dot dl through an unbiased diode, you get a voltage! Diodes violate KVL!
(https://i.stack.imgur.com/SaSH6.jpg)
Obviously using integral of E dot dl has a problem. Circuits with diodes would be another KVL fail according to Dr. Lewin's definition.
This diagram shows a diode with a current flowing trough it. In such a case all semiconductors show a voltage drop that can indeed be measured with a voltmeter.
In a rest state any voltage created on the junction is subtracted back out once the semiconductor connects to the copper pins. If a diode was to create a voltage in such a conduction this would mean i will also have to be capable of pushing current in that direction of voltage.
So what does a voltmeter measure? Well it actually measures the current trough its internal resistance and then displays what voltage it takes to push such a current. Notice how in Dr. Lewins example the voltage across the resistors is always defined as a single value. In the same way it is defined to have a single value across the terminals of a voltmeter. Since an ideal resistor has zero physical dimension, means that it is impossible to generate any magnetic EMF across it (It can't be part of a surface area edge as it has no length) and a external electrostatic field can't produce a gradient sharp enough to pull electrons along. So the only "electron pusher" that remains to convince electrons to flow trough the resistor is the difference in charge density on the resistors terminals. The crowded electrons on one end want to get trough to the not as crowded electrons on the other end. Hence why the voltmeter ends up showing a difference in charge density across its terminals.
But it is possible to have EMF generated on a resistor that has physical length. Its basically the combination of a wire and a resistor (And can be lump modeled as such if desired). In the same way a voltmeter that's longer than zero will read EMF across itself. But its only the EMF induced in the section that the voltmeters size occupies. So the larger the voltmeter the more EMF it will show on the display. This just makes things more confusing so we say voltmeters have zero size so they don't read any EMF.
You have electrochemical potential as well as electrostatic potential and induced EMF that can all move charge. The voltmeter can't tell the difference between them.
So you are still saying that EMF is located at specific segments of the loop.
I'm just someone who had some time recently to play with openEMS and see if I could reproduce something similar to the Romer experiment
So you need to apply a similar voltage step response across your solenoid coil (Not just a pulse). Also your time scale appears to be very short in the simulation. The pulse you applied seams to last only a few picoseconds, this gives it a bandwidth of >100GHz and hence why you get funny behavior as you are mostly simulating radio waves traveling around your scene. The whole simulation only lasting what appear to be around half a nanosecond. My experiment had the pulse last 500 microseconds so about 1 000 000 times longer than your simulation time.
Besides my suggestion to add core material to form solenoid,See the Romer paper where "iron core" is specifically mentioned (and not used).
QuoteBesides my suggestion to add core material to form solenoid,See the Romer paper where "iron core" is specifically mentioned (and not used).
I think this would be a good simulation for you to try now that you have the source.
You shall show time and voltage units used in X&Y scales. Now we can only guess - excitation pulse period is 100 seconds, 100 femtoseconds or what?
I tried to organize my thoughts about the whole thing here https://grumpyengineering.wordpress.com/ (only one post there for now) if you want to read them.
I tried to organize my thoughts about the whole thing here https://grumpyengineering.wordpress.com/ (https://grumpyengineering.wordpress.com/) (only one post there for now) if you want to read them.
I tried to organize my thoughts about the whole thing here https://grumpyengineering.wordpress.com/ (https://grumpyengineering.wordpress.com/) (only one post there for now) if you want to read them.
When you talk about advanced stuff like Faraday's law, you shall not ignore other laws like law of conservation of energy (https://en.wikipedia.org/wiki/Conservation_of_energy).
Pay close attention to following post made by proponent of Dr.Lewin (https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/msg1961348/#msg1961348) to see where exactly you and Dr.Lewin made mistake.
QuotePay close attention to following post made by proponent of Dr.Lewin (https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/msg1961348/#msg1961348) to see where exactly you and Dr.Lewin made mistake.
I don't see an issue here, but feel free to point it out if you like.
QuotePay close attention to following post made by proponent of Dr.Lewin (https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/msg1961348/#msg1961348) to see where exactly you and Dr.Lewin made mistake.
I don't see an issue here, but feel free to point it out if you like.
Your (and Dr.Lewin's) equation does not separate EMF (energy) source from load, incorrectly and blatantly saying that KVL is as follows:
(https://s0.wp.com/latex.php?latex=%5Coint+%5Cvec+E+%5Ccdot+d%5Cvec+l+%3D+0&bg=ffffff&fg=333333&s=4)
Kirchsoffs CIRCUIT law requires circuit consisting of energy source and load.
Correct equation would be:
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=570254;imag)
It's not "my" equation. It's how Lewin defines KVL. I'm not sure why you think it can't be rewritten to explicitly show sources and loads. It would look like this.
(https://s0.wp.com/latex.php?latex=%5Coint+_%7Bsources%7D+%5Cvec+E+%5Ccdot+%5Cvec+dl+%2B+%5Coint+_%7Bloads%7D+%5Cvec+E+%5Ccdot+%5Cvec+dl%3D+0+&bg=ffffff&fg=333333&zoom=2)
When you said "Your (and Dr.Lewin's) equation does not separate EMF (energy) source from load". I suppose you didn't explicitly say it can't be rewritten, but you seemed to be implying that for some reason it couldn't. Anyways, I'm glad we agree on this.It's not "my" equation. It's how Lewin defines KVL. I'm not sure why you think it can't be rewritten to explicitly show sources and loads. It would look like this.
(https://s0.wp.com/latex.php?latex=%5Coint+_%7Bsources%7D+%5Cvec+E+%5Ccdot+%5Cvec+dl+%2B+%5Coint+_%7Bloads%7D+%5Cvec+E+%5Ccdot+%5Cvec+dl%3D+0+&bg=ffffff&fg=333333&zoom=2)
Right. BTW where I did say that I think it can't be rewritten?
Look, whole idea of "KVL does not work" proof is based on statement that integral of E.dl for the loop equals zero, thus EMF equals zero which is as Dr.Lewin say impossible.In a typical batteries+resistors type circuit, the EMF is the batteries, and they are included in the E•dl integration. I wrote this out explicitly in my last post where the source and loads were specified in separate integrations (i'm not even sure if this is proper notation but I think you get the point). Saying that E•dl equals zero means the EMF must equal zero is not correct, and I don't believe Lewin ever said that (please link with timestamp if he did). Rather, the point is that using KVL (as defined by Lewin as E•dl = 0) will yield the wrong answer in the presence of time varying magnetic flux, and the reason it yields the wrong answer is that now we have an EMF that doesn't come from an electric field.
Indeed it is impossible - because equation is incomplete, thus statement is futile.Of course it's incomplete, that's Lewin's point. And the way to complete it is to update it to Faraday's law. If you disagree I'd ask you how you would complete it.
You just corrected it by writing EMF + ( -I*R ) = 0. If you agree then we are done. You disproved Dr.Lewin.As I mentioned in the previous post, there was a minus sign missing. In the drawing, the assumption is we're looking at a specific point in time where the emf from the solenoid is 1V. The value of the evenly distributed resistance will determine the value of the current (if it's total 1ohm, we get 1A, etc.). Either way, if you start from Faraday's law, you have 1V on both sides of the equation (both sides better be the same value otherwise we either screwed up or Faraday's law is somehow wrong). If you move that 1V over to the left then you're effectively saying 1V - 1V = 0V. Not a very enlightening statement and the spirit behind Lewin's "5 + 3 - 8 = 0" video.
Of course it's incomplete, that's Lewin's point. And the way to complete it is to update it to Faraday's law. If you disagree I'd ask you how you would complete it.
In addition to asking how you would complete Lewin's KVL (Int E•dl = 0) to make it correct (I agree that it is not universally correct), I think I should ask you to clarify exactly what it is that you think Lewin has done incorrectly so we can make some progress in understanding each other.
Of course it's incomplete, that's Lewin's point. And the way to complete it is to update it to Faraday's law. If you disagree I'd ask you how you would complete it.
That's the whole point - you cannot use incomplete equation to prove anything! Integral E.dl = 0 of Kirchoff's circuit rule includes *both* EMF source and load. Integral E.dl of Maxwell's equation includes/describes only EMF *source*. You completed it for me:
(https://ibin.co/w800/4RCvdo3HWTGP.png)QuoteIn addition to asking how you would complete Lewin's KVL (Int E•dl = 0) to make it correct (I agree that it is not universally correct), I think I should ask you to clarify exactly what it is that you think Lewin has done incorrectly so we can make some progress in understanding each other.
Move right side (load) of equation you just completed to left side and I am done showing where Dr.Lewin was wrong. It will be in front of your eyes contradicting with what you say in your blog:
The point there is that something can't be simultaneously zero and non zero.
but.. it's not. int E•dl is int E•dl is int Ed•dl. It has the same meaning in both Lewin's KVL and Faraday's law. It means you go around a loop adding up each incremental bit of E field you encounter along your path. It doesn't matter whether it's an E field from a battery or an E field in a resistor or an E field arising from a changing magnetic flux. Do you believe that int E•dl has somehow a different meaning in the two equations?The point there is that something can't be simultaneously zero and non zero.
It can - when "something" is one thing in one case and completely different in another.
Take following as my objection you asked for: you cannot take in account law of conservation of energy in KVL case but ignore it in Maxwell's.
Shall I repeat & emphasize : Integral E.dl part of Kirchoff's circuit rule includes *both* EMF source and load. Integral E.dl of Maxwell's equation includes/describes only EMF *source*.
You simply can't equal two (integrals), because they "look the same" (your words BTW).
Following equation describes circuit of Dr.Lewin's experiment inner loop:
(https://ibin.co/w800/4RDW0KhA0NN6.png)
Don't you find it similar to equation of KVL you wrote?
(https://s0.wp.com/latex.php?latex=%5Coint+_%7Bsources%7D+%5Cvec+E+%5Ccdot+%5Cvec+dl+%2B+%5Coint+_%7Bloads%7D+%5Cvec+E+%5Ccdot+%5Cvec+dl%3D+0+&bg=ffffff&fg=333333&zoom=2)
I assume you agree to both. Me too.
OK now we're getting somewhere, i think (i hope!). If I understand you correctly, you believe that Faraday's law implies a violation of conservation of energy!
"you cannot take in account law of conservation of energy in KVL case but ignore it in Maxwell's." I would call this a strawman, unless you can point me to where Lewin said that Maxwell's equations require ignoring conservation of energy.
It's his KVL that violates conservation of energy in his experiment because it can't possibly account for the source of energy as it knows nothing about magnetic flux!
I would say that as applied to this experiment, Faraday's law equates Int E•dl with the source (negative time rate of change of magnetic flux through the loop) of energy. It seems like you are unwilling to accept an EMF that doesn't arise from a source that is clearly related to an E field being maintained between two points, and that's what's causing you trouble, but that's the reality that Faraday describes.
If you don't believe Maxwell's equations always apply, or you think they violate conservation of energy, then I'm afraid we can't go anywhere from there.
LOL. Here we go. Again. When out of arguments - just state that debate opponent does not understand Maxwell's equations. :horse:
I never said or implied that I do not believe Maxwell's equations. Also I never said that they violate law of conservation energy.
I can't go anywhere from there.
LOL. Here we go. Again. When out of arguments - just state that debate opponent does not understand Maxwell's equations. :horse:
LOL. Here we go. Again. When out of arguments - just state that debate opponent does not understand Maxwell's equations. :horse:
You don't. But that's not your fault. Maxwell's equations show how Nature is much weirder than we may conceive. You'll have to reboot your brain to understand it...
I can't go anywhere from there.
Yes. Please. Stop this :blah: nonsense of pretending that you do not understand what I mean. Our discussion looks like broken record.
I can't help but feel all of the drama around this could have been avoided if electronics educators did a better job of adding caveats and asterisks to their materials and explanations. I went to UC Berkeley and I'm pretty sure not a single professor ever uttered the words "lumped circuit abstraction" in my entire undergrad career. Agarwal is doing God's (or rather Feynman's) work.
If you still disagree with the above I would love to hear from you, but I believe, most of the confusion results from disagreements about what KVL is.
The algebraic sum of all the voltages around any closed loop in a circuit is equal to zero
Nobody in this thread is trying to prove that Maxwells equations are wrong
This is proabobly the most important realization you made Mhz:On the contrary, that's exactly where the previous discussion with ogden led, with them concluding that Maxwell's equations are only correct in specific situations (superconducting rings, I believe is what was said). That's another way of saying that sometimes they are wrong.
https://grumpyengineering.wordpress.com/
Quote
If you still disagree with the above I would love to hear from you, but I believe, most of the confusion results from disagreements about what KVL is.
Nobody in this thread is trying to prove that Maxwells equations are wrong, stop blaming people for that.
Most of the arguing between the "Kirchoff" and "Maxwell" sides is due to both sides having a different idea of what KVL is. I fully agree that if KVL is what Dr. Lewin explains it as being then its garbage as soon as you have changing magnetic fields. I have no idea where he got that definition of KVL, everywhere i see it defined as the flowing:
Quote
The algebraic sum of all the voltages around any closed loop in a circuit is equal to zero
It explicitly mentions all voltages, this includes the electric field as well as the EMF (I think we all agree EMF is a voltage). Also notice that it mentions an algebraic sum (This is not an integral!) since KVL is not a law of the universe but a tool for analyzing circuit mesh models.
Both the "Kirchoff" and "Maxwell" sides are correct! The only only reason that we are arguing is because the so called "Maxwell" side is using a less useful interpretation of KVL. The people on the "Kirchoff" side are not denying anything about Maxwells equations, the only thing this side is trying to say is that you can use KVL to solve Lewins paradoxic circuit just fine i you use KVL correctly. You indeed CAN NOT USE Kirhoffs laws for everything, but this particular circuit is not such a case.
The "Kirchoff" side should actually be named "Kirchoff and Maxwell" side. We are happy to use one or the other rather than swear by Maxwell only, just a matter of the right tool for the job. Is there something wrong with that?
I'd invite you to redraw the diagram and use the "modified" KVL on this circuit. See if you can model it in a way that doesn't falsely localize the effect of the mutual inductance but that allows you to get the correct answer with the "modified" KVL. It would help if you post the drawing of the updated model for us.
On the contrary, that's exactly where the previous discussion with ogden led, with them concluding that Maxwell's equations are only correct in specific situations (superconducting rings, I believe is what was said). That's another way of saying that sometimes they are wrong.
I do not talk about abstract KVL and Maxwell equation "cases". I talk about equations that describes circuit of experiment. Everything seemingly is ok with KVL simple int E.dl = 0, yet I would prefer to split it into EMF source and load, as you already did - thank you for that. Problem arises when Dr.Lewin use plain Maxwell's equation and say that it miraculously tells everything about inner loop of his experiment. I disagree. Maxwell's equation is just EMF source part! Where's physics of load (resistors) in Maxwells equation? If you leave it like that, then it is indeed violation of conservation of energy. Plain Maxwell's equation can be used only to describe superconductive ring (w/o embedded resistors) placed in changing magnetic flux.
I disagree with the thread title.
Walter Lewin used to be a master. Then he started flinging poo at good people.
So i vote we take Master status from him. :-DD
Ok so my point is this, you've modeled the circuit with lumped elements and that gives something that looks correct, but if you set this experiment up in real life, do you really think you'll measure any significant voltage across any of L2, L3, L4 or L5 like spice would tell you is there? The coupled flux isn't confined in those points so you won't.
Ok so my point is this, you've modeled the circuit with lumped elements and that gives something that looks correct, but if you set this experiment up in real life, do you really think you'll measure any significant voltage across any of L2, L3, L4 or L5 like spice would tell you is there? The coupled flux isn't confined in those points so you won't.
So you say that Kirk T. McDonald is wrong in chapter "2.3 Comments" (page 10) (http://www.physics.princeton.edu/~mcdonald/examples/lewin.pdf)? Please tell where and why he is wrong. Prove him wrong.
Excerpt:
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=605980;image)
Suppose a voltmeter were connected to two points on the upper wire between resistors 1
and 2, as shown in the sketch below. The voltmeter loop is not coupled to the solenoid, so
there is no (or extremely little) EMF induced in this loop, and hence I1 = 0, and the meter
reading would be Vmeter = 0.
Do you see the above two equations as equivalent term by term?
I was talking about the Fermi levels of the separated materials, what Neamen call 'intrinsic Fermi levels' when referring to the compound structure. At thermodynamic equilibrium there are no longer Fermi levelS. But yes, out of equilibrium the one Fermi level of the structure splits in separate levels and the voltage corresponding to that difference is what is measured.Besides, the difference in Fermi levels is the barrier potential (if we agree on how to treat the sign). I guess [NOTE: I should have written 'thought', instead of 'guessed') you were the one saying that you cannot read it with a voltmeter.With no bias, in equilibrium, the Fermi levels on both terminals are equal, so zero voltage. Refer to figure 7.3 of Neamen.
You have to wonder if "potential barrier" is the right phrase for an ohmic contact, which should have little or no barrier.
So what's your point? Are you saying that there is no net electrostatic potential across the diode terminals?
Did you even read that section?
QuoteSuppose a voltmeter were connected to two points on the upper wire between resistors 1
and 2, as shown in the sketch below. The voltmeter loop is not coupled to the solenoid, so
there is no (or extremely little) EMF induced in this loop, and hence I1 = 0, and the meter
reading would be Vmeter = 0.
This agrees with what @mhz said.
In that section, Dr. McDonald is pointing out that a voltmeter does not read the difference in scalar potential.
Do you see the above two equations as equivalent term by term?
I did say "Don't you find it similar". I did not say equivalent, especially term by term. One more illustration of troll & "coach expert" tactics. You just cherrypick out of context whatever you find convenient for you, ignoring what I was ACTUALLY talking about: circuit that has EMF source and load, that both equations describes such and are similar in such sense.
Integral E.dl = 0 of Kirchoff's circuit rule includes *both* EMF source and load. Integral E.dl of Maxwell's equation includes/describes only EMF *source*.
Have you ever tried to compute the integral of E.dl of a RLC circuit with a generator
Ok so my point is this, you've modeled the circuit with lumped elements and that gives something that looks correct, but if you set this experiment up in real life, do you really think you'll measure any significant voltage across any of L2, L3, L4 or L5 like spice would tell you is there? The coupled flux isn't confined in those points so you won't.
So you say that Kirk T. McDonald is wrong in chapter "2.3 Comments" (page 10) (http://www.physics.princeton.edu/~mcdonald/examples/lewin.pdf)? Please tell where and why he is wrong. Prove him wrong.
Excerpt:
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=605980;image)
As rfeecs pointed out, McDonald echoes what I said to Berni, that the voltmeter will measure zero
Have you ever tried to compute the integral of E.dl of a RLC circuit with a generator
No. Have you?
I use L(di/dt) with real inductors/transformers having inductance and saturation current specs.
Works for me well.
Does not look like that, from this side of the monitor.
To not repeat a certain arrangement i will also answer this for both definitions of voltage:
A) For definition "Voltage is the integral of all forces pushing on electrons along a given path connecting two points":
The inductors L2 L3 L4 L5 have zero voltage across them at all times (Zero resistance). Any EMF voltage induced in the wire by the magnetic field is instantly countered by the charge separation of electrons.
B) For definition "Voltage is the difference in charge density between two points" (This is what real life voltmeters show)
The inductors L2 L3 L4 L5 have a voltage drop that sums up to the same voltage as the total voltage drop on the resistors. This voltage in the wire is caused by charge separation pushing electrons towards one end of a wire, resulting in more electrons on one end hence higher voltage on one end.
The proper textbook definition (A) is the one that is used in Dr. Lewins example where he gets two different voltages across the same two points. This is fully correct and there are indeed two voltages there. The reason for the two solutions is that this voltage is including the EMF voltage from the magnetic field, yet the loop is not closed yet as the two points are in different locations in space. Depending on how this path is closed results in a different solution for the EMF voltage and this changes the result. Hence why voltage is path dependent.
So why are we using the other definition (B) if its clearly wrong? Well turns out in real life its rather tricky to measure the voltage according to that definition. Electrical components (such as resistors) represent only a small part of the path around the magnetic fields loop area, because of this all of the electron pushing work is done by the electrical field (caused by charge seperation). Turns out all the voltmeters are actually devices that measure current trough the internal resistance and display the voltage required to push that current. The density of electrons at a point in space can only have 1 single defined value hence why these voltages always have one value rather than multiple. All of this simply makes this definition (B) more useful and as such is used in circuit analysis and spice simulations. Since circuit analysis uses it that forces KVL to use it too.
In the absence of a changing magnetic field around the circuit both definitions of voltage have the same value so it doesn't matter what you use. But in a magnetic field it does matter a lot.
As for the lumped model, it only hides what you want it to hide. Many many tiny inductors in series act the same as one big inductor, so it makes it easier to use a lumped version. Once you lump a segment of a circuit all voltages within the lumped part become meaningless, this is why lumping the inductor as a single one causes problems in this example. The lumping procedure also lumped all our points of interest and messed them up, they no longer show true voltages. However anything outside the area we just lumped is preserved. The rest of the circuit doesn't care how many inductors there are, it just sees a set inductance value across the points. So by only lumping sections of the wire that have no points of interest we preserve all the points we want to measure. Hence why all the points on the ends of the inductors have the correct voltage values.
All wires have some amount of mutual inductance to each other as long as they are not placed at perfect right angles. In this case there is more to it however. The inductors L2 L3 L4 L5 are actually a single inductor (single whole turn of the loop) that has been sliced up in to 4 parts. Because they are part of the same inductors means they share the same magnetic flux and hence are highly coupled inductors. The inductors L6 L7 L8 L9 are another inductor that has been sliced up in to quarters, but since the wire follows the same path as the inner cirucit means that any flux passing trough that loop passes trough this one too. This means all of them are coupled to each other (aka a transformer). The solenoid coil in the middle is also having the same magnetic flux pass trough it hence why its also coupled. In my simulation it has a ideal coupling coefficient of 1, but in reality it would be lower because solenoid is smaller than the loop so some of the flux escapes.
So yeah we are mostly looking at two sides of the same coin here. Its two different ways of explaining the same thing.
As rfeecs pointed out, McDonald echoes what I said to Berni, that the voltmeter will measure zero
He says exactly opposite: "the result Vmeter = 0 is appealing in that we might naïvely expect the “voltage drop” to be zero between points along a good/perfect conductor.".
You really shall read last paragraph of mentioned chapter carefully.
I have been, and I have to admit I'm quite perplexed with it. In particular equation 35 doesn't seem correct to me. For example, if we assume a point in time where I = 1mA, R1 = 100ohm, R2 = 900ohm, R = 1Mohm and I1 ≈ 0 (as he states) then he seems to be saying 0V = -1V. If someone can help clear this up for me I'd appreciate it.
I have been, and I have to admit I'm quite perplexed with it. In particular equation 35 doesn't seem correct to me. For example, if we assume a point in time where I = 1mA, R1 = 100ohm, R2 = 900ohm, R = 1Mohm and I1 ≈ 0 (as he states) then he seems to be saying 0V = -1V. If someone can help clear this up for me I'd appreciate it.
Equation is correct indeed. Thou it is counterintuitive. Wire segment "a-b" is part of *both* loops - loop of leads and loop containing R1 and R2. Leads loop does not have any EMF induced, source of "voltage drop" in particular wire segment is EMF generated only in the loop containing resistors. All this is not that important. Important part is: voltage will be observed which is contrary to your statement.
[edit] No, you dont'use Ohms law here. You shall use Maxwell's equation to calculate EMF generated in wire segment "a-b"
[edit1] Seems, I know where your frustration comes from. By saying I1=0 he means that current induced by EMF is zero because there is no EMF in the voltmeter leads. On the other hand current will be flowing through voltmeter due topotential difference"voltage drop" between points a & b. This is my explanation. Hope it helps.
I have been, and I have to admit I'm quite perplexed with it. In particular equation 35 doesn't seem correct to me. For example, if we assume a point in time where I = 1mA, R1 = 100ohm, R2 = 900ohm, R = 1Mohm and I1 ≈ 0 (as he states) then he seems to be saying 0V = -1V. If someone can help clear this up for me I'd appreciate it.
Equation is correct indeed. Thou it is counterintuitive. Wire segment "a-b" is part of *both* loops - loop of leads and loop containing R1 and R2. Leads loop does not have any EMF induced, source of "voltage drop" in particular wire segment is EMF generated only in the loop containing resistors. All this is not that important. Important part is: voltage will be observed which is contrary to your statement.
[edit] No, you dont'use Ohms law here. You shall use Maxwell's equation to calculate EMF generated in wire segment "a-b"
[edit1] Seems, I know where your frustration comes from. By saying I1=0 he means that current induced by EMF is zero because there is no EMF in the voltmeter leads. On the other hand current will be flowing through voltmeter due topotential difference"voltage drop" between points a & b. This is my explanation. Hope it helps.
Thanks for the reply. I annotated his drawing to make my confusion clearer (heh).
(https://ibin.co/4ROonqRN5Cu3.png)
The equation in question, repeated is
(https://ibin.co/4ROe8sZbEx99.png)
Green is the path integral on the left side of the equation and red is the path integral on the right side of the equation. Would be great if you can fix it so that the equation balances. By all means use Maxwell's equations to get there.
I suspect I'm not going to fully understand McDonald until I've completely grokked his discussions on vector potential.
I suspect I'm not going to fully understand McDonald until I've completely grokked his discussions on vector potential.
I suspect I'm not going to fully understand McDonald until I've completely grokked his discussions on vector potential.
(https://ibin.co/4ROonqRN5Cu3.png)
Oh, my... You use Ohms law to claim that voltage between a-b is 1V? :palm:
I don't even know what to say. How dare you pretend that you mastered Maxwell's equations?!
First, you have to know azimuthal angle between two points, a & b. Let's assume it is PI/4 (45 degrees). According to your data EMF of the resistor loop is 1V. We put 1V and Pi/4 into equation (34): 1V*(Pi/4)/(2*Pi) = 1/8 V. Voltmeter shall show 0.125V in such case (when angle is 45 degrees).
[edit] Forget about "I1=0". It is misleading or even incorrect.
Have you ever tried to compute the integral of E.dl of a RLC circuit with a generator - a lumped circuit, just to see that Kirchhoff and field theory can agree if there is no dB/dt area enclosed by the circuit path? It might clear a lot of things up before trying to attack a non-lumped circuit such as Lewin's.
Int E•dl in the wires is 0V (no E fields in perfect conductors, or next to none in real conductors in which case we approximate to 0) and in the resistor is equivalent to I*R (if not then what do you think the contribution of Int E•dl through the resistor is?).
Your response contradicts several of the things McDonald says in his paper, namely that the voltmeter will read 0V (not 0.125V) and that I1 = 0 is misleading/incorrect. So now who should I believe, you or McDonald?
Anybody else wanna take a crack at this?
[edit1] Seems, I know where your frustration comes from. By saying I1=0 he means that current induced by EMF is zero because there is no EMF in the voltmeter leads. On the other hand current will be flowing through voltmeter due topotential difference"voltage drop" between points a & b. This is my explanation. Hope it helps.
I have been, and I have to admit I'm quite perplexed with it. In particular equation 35 doesn't seem correct to me. For example, if we assume a point in time where I = 1mA, R1 = 100ohm, R2 = 900ohm, R = 1Mohm and I1 ≈ 0 (as he states) then he seems to be saying 0V = -1V. If someone can help clear this up for me I'd appreciate it.
(https://ibin.co/4ROe8sZbEx99.png)
[Edit 1: fix typos]
I agree equation 35 does not look correct, maybe it is a typo. He seems to have left out the EMF term.
Int E•dl in the wires is 0V (no E fields in perfect conductors, or next to none in real conductors in which case we approximate to 0) and in the resistor is equivalent to I*R (if not then what do you think the contribution of Int E•dl through the resistor is?).
Faradays law? ... Maybe? From your blog BTW:
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=606070;image)
Your response contradicts several of the things McDonald says in his paper, namely that the voltmeter will read 0V (not 0.125V) and that I1 = 0 is misleading/incorrect. So now who should I believe, you or McDonald?
Anybody else wanna take a crack at this?
I do not contradict with McDonald. You do. I will repeat again what he says: "the result Vmeter = 0 is appealing in that we might naïvely expect the “voltage drop” to be zero between points along a good/perfect conductor." He even shows equation (34) how to calculate voltage between a-b points.
That is Faraday's law yes, how would you use it to calculate the contribution of the line integral of E•dl through the resistor?
You said "Voltmeter shall show 0.125V."
McDonald said "the result Vmeter = 0 ..."
That is Faraday's law yes, how would you use it to calculate the contribution of the line integral of E•dl through the resistor?
Why you suddenly introduce resistor here? We talk about Maxwell's equations and Faradays law. Note that wire segment a-b does not contain any resistor.
QuoteYou said "Voltmeter shall show 0.125V."
Yes. I demonstrated you how to calculate voltage between a-b in case angle is 45 degrees. McDonald provides only formula, not actual calculation. Where's your problem to understand that?QuoteMcDonald said "the result Vmeter = 0 ..."
If you cannot comprehend that McDonald says that it is naïve to expect that voltmeter will show 0V, then our discussion is finished here and now. When you confirm that you can read - we may continue.
I didn't suddenly introduce it. It's inside one of the path integrals in equation 35 which is what I've been talking with you about for these past several posts. I now see that you were still referring to the arc a-b and using equation 34 when you said "Oh, my... You use Ohms law to claim that voltage between a-b is 1V? :palm:"
I'm fully able to plug the same numbers into equation 34 as you are. You keep responding to my questions about equation 35 with equation 34.
I have been talking about equation 35 for these past several posts and it's now clear that you've been ignoring them and persisting at talking about equation 34. We're not even talking about the same thing.
"our discussion is finished here and now"
Sounds good to me.
To not repeat a certain arrangement i will also answer this for both definitions of voltage:
A) For definition "Voltage is the integral of all forces pushing on electrons along a given path connecting two points":
The inductors L2 L3 L4 L5 have zero voltage across them at all times (Zero resistance). Any EMF voltage induced in the wire by the magnetic field is instantly countered by the charge separation of electrons.
B) For definition "Voltage is the difference in charge density between two points" (This is what real life voltmeters show)
The inductors L2 L3 L4 L5 have a voltage drop that sums up to the same voltage as the total voltage drop on the resistors. This voltage in the wire is caused by charge separation pushing electrons towards one end of a wire, resulting in more electrons on one end hence higher voltage on one end.
Where does definition B come from? Charge density and Voltage don't even have the same units. [C/m3] vs [J/C]
I disagree. You can split the total mutual inductance M of the loop into two strings of as many inductors as you want in spice. The value you measure in spice will not be the actual scalar voltage potential between the ends of the resistors (which is approximately zero as measured by the voltmeter). Lumping can't be done in this kind of circuit in spice without creating false outcomes.
I see now that you're trying to model the mutual inductance of the "outer loop" i.e. the path formed by the two measurement loops, but not going through R1 and R2. You've arranged the coupling dots in a way that the inner inductors and outer inductors cancel each other out in a way that satisfies there being no flux coupling in the two measurement loops.
I disagree with the thread title.
Walter Lewin used to be a master. Then he started flinging poo at good people.
So i vote we take Master status from him. :-DD
A mark of distinction of those who criticize Lewin is their utter and declared inability to teach Maxwell.
Is it still OK to use a voltmeter? Or is every measurement suspect now?
Is it still OK to use a voltmeter? Or is every measurement suspect now?
To be fair, he did issue an apology video. Don't know if it's already been linked to here.
Is it still OK to use a voltmeter? Or is every measurement suspect now?
Those meter measurements were always suspect in certain situations.
Is it still OK to use a voltmeter?
Or is every measurement suspect now?
Regarding McDonalds 'paper' (has that been published on a peer reviewed paper?), let me quote this comment George Hnatiuk from a youtube discussionQuoteI found several errors in the "Lewin's Circuit Paradox" paper back in June to which I alerted Dirk and company and the paper has since been edited with NEW errors introduced and some of the older ones still present. It is very sloppy work at best and nothing I would expect from a university staff member.
As I said before, you should try to analyze how the lumped circuit simplifications come about before tackling non-lumped circuits like Lewin's ring.
Ok. Fair enough. Nobody's perfect. That's why peer review practice is so important and McDonald do error corrections. Could you provide (link to) Dr.Lewin's paper regarding subject, supposedly peer-reviewed?
As I said - when you read McDonald's paper you will see that Dr.Lewin's circuit can be analyzed as circuit of lumped elements. If you disagree, then prove opposite - tell where and how McDonald is wrong.
In the inner loop of Dr.Lewin's experiment E fields can be expressed as E = E.coloumb + E.induced. Wire loop is responsible for E.induced, we can say it is EMF source. As resistance of the wire is very small compared to resistors we ignore it so all the E.coloumb field is located in the resistors - those are load.
Why, it's Romer's paper - it's funny you did not realize it
QuoteAs I said - when you read McDonald's paper you will see that Dr.Lewin's circuit can be analyzed as circuit of lumped elements. If you disagree, then prove opposite - tell where and how McDonald is wrong.
Maybe you are misunderstanding McDonald as well.
E_coulomb kills E_induced in the wires
Romer's paper is about the very same experiment made by Lewin, and it reaches the very same conclusions.
So, since real life voltmeters have (to my knowledge) no way to tell the E_coulomb and the E_induced apart but only see the effect of the resulting total field, it makes little sense to ascribe to the [difference in the values of the] scalar potential any meaning besides that of the voltage measured along a very special class of paths.
And he didn't start with "Hello, hello, hello!" as well. Then they must have found completely different results.
What I see is that they both find that the voltage is dependent on the path, and that when placed on the outside of the loop the voltmeters - applied to the very same two points - give different and opposite phase reading.
Quote"what's the summary field (integral E.dl ) of the loop E = E.coloumb + E.induced?" You did not gave clear answer. Is it zero or not?Here's the answer, assuming that with 'summary' you mean circulation along the circuit's path: the circulation of E_total (integral of (E_coloumb + E_induced) . dl along the circuit's path is equal to minus the time derivative of the flux of B linked by said path.
Yes, it's Faraday's law.
Please do yourself and anybody else a favor: get hold of a copy of "Fields and Waves in Communication Electronics" by Ramo, Whinnery and VanDuzer and read the first four pages of chapter 4 (The electromagnetics of circuits)...
To be fair, he did issue an apology video. Don't know if it's already been linked to here.
Yes it was mentioned here "many pages of posts" ago. Dr.Lewin is one of greatest physics teachers known, he deserves all the titles received.
Punishment shall be proportionate. MIT may revoke his emeritus title, harassed women may seek justice in the court, but come on - removing all his life's work, his courses and lectures from all MIT teaching platforms is way too much. MIT punished not only Dr.Lewin but many, many students. Luckily we have youtube and hopefully social justice warriors of MIT will not do anything about it. We shall not burn scientist with all his books/works/videos just because he made some mistake in his life.
Was he involved in some sexual scandal or something?
He became of #metoo target, due to his own human error. As I already said - I do not agree. Such issues shall be resolved in/by court, not by directorate of MIT - by literally burning all his work, by punishing his students, not actually punishing himself.
Please do yourself and anybody else a favor: get hold of a copy of "Fields and Waves in Communication Electronics" by Ramo, Whinnery and VanDuzer and read the first four pages of chapter 4 (The electromagnetics of circuits)...
I guess you really like that book.
It was my textbook in college 37 years ago for "Electromagnetic Fields and Waves" EECS117A, B, and C. The teacher was Theodore Van Duzer.
As an argument I was referring to scientific paper having peer review and corrections. All you have in return is youtube video with introduction "Hello, hello, hello", no written content and no peer review? Whatta crooked mirrors world you are living in?!
QuoteWhat I see is that they both find that the voltage is dependent on the path, and that when placed on the outside of the loop the voltmeters - applied to the very same two points - give different and opposite phase reading.What?!! Your whole proof is two voltmeters showing different signs?
QuoteQuote"what's the summary field (integral E.dl ) of the loop E = E.coloumb + E.induced?" You did not gave clear answer. Is it zero or not?Here's the answer, assuming that with 'summary' you mean circulation along the circuit's path: the circulation of E_total (integral of (E_coloumb + E_induced) . dl along the circuit's path is equal to minus the time derivative of the flux of B linked by said path.
Yes, it's Faraday's law.
So you refuse to name number because you either do not know it of refuse to acknowledge it being zero?
QuoteIt was my textbook in college 37 years ago for "Electromagnetic Fields and Waves" EECS117A, B, and C. The teacher was Theodore Van Duzer.
Woah, how was he?
The reason I'm bringing RWvD up so many times is that it has a really nice discussion on the origin of KVL and KCL from Maxwell's equations, and of course the fact that ogden seems impervious to reading it.
I have a question. Why wouldn't a simple loop of wire show that "Kirchhoff is for the birds"? (Or even a straight wire)
Also, in one of his videos does Lewin say something like "The oscillioscope on the left measures the voltage across the left resistor." How does he know which one it is measuring?
I agree the book is pretty good. I have referred back to it myself when I realize that I forgot some basic things and it immediately refreshed my memory with it's basic and direct approach. It does require vector calculus, so maybe not for everyone. That's just the nature of the subject.
The peer-reviewed scientific paper backing Lewin's "Hello hello hello" videos is Romer's paper. I had hoped it was clear.
Quote"what's the summary field (integral E.dl ) of the loop E = E.coloumb + E.induced?" You did not gave clear answer. Is it zero or not?Oh, for... ****'s sakes!
It's not zero. The value depends on the time-varying flux: it is equal to minus the time derivative of the flux of B linked by said path. Didn't I just tell you that?
You want a value? In the case of Lewin's experiment, IIRC, it's 1V.
Quote"3) Do you agree that integral E.dl for this circuit is zero at any given time of observation?"Absolutely not.
Do you realize that the circuit you are proposing is just Lewin's ring with one resistor?
After all, when you compute the circulation of E_total = E_conservative + E_induced you get the sum of the circulation of E_conservative which is zero and all that's left is the circulation of E_induced. Everything checks out.
After all, when you compute the circulation of E_total = E_conservative + E_induced you get the sum of the circulation of E_conservative which is zero and all that's left is the circulation of E_induced. Everything checks out.
Wait... E.conservative in the resistor is zero even when on it's terminals is 1V? Are you sure?
After all, when you compute the circulation of E_total = E_conservative + E_induced you get the sum of the circulation of E_conservative which is zero and all that's left is the circulation of E_induced. Everything checks out.
Wait... E.conservative in the resistor is zero even when on it's terminals is 1V? Are you sure?
I was talking about the circulation. You have to close the loop.
Fever has gone up, I will check again tomorrow, if I survive the night :-)
Fever has gone up, I will check again tomorrow, if I survive the night :-)
I hope you get better soon.
Yes, get better soon Sredni. Thank you for sharing your insights and knowledge in this thread.
The only thing you have to do is imagine the magnetic field as a electric field that is circulating around the changing magnetic flux lines.Why would you do that? The changing magnetic field produces an electric field. The electric field lines are circles around the magnetic field as shown in post #16:
Once you do that you have only electric fields acting on electrons and those are always conservative so you never get multiple answers for what voltage is between two points.If you have electric field lines that form a loop, as in this case, you have a nonconservative field.
And this voltage happens to be the exact same voltage voltmeters are showing.So you don't have two voltmeters connected to same point showing different voltages? This is what happens in the experiment. Or are we supposed to imagine that it doesn't?
Its just a different way of calculating the same thing, except that this way gives less confusing answers (Particularly in this kind of cirucit)
The two voltmeters will only measure the same voltage if the voltmeters and their connecting wires are outside the field region or somehow shielded or arranged so that the field does not affect the measurement. Fine, but that is not this experiment. This experiment is set up to demonstrate Faraday's law and non conservative fields.
Meanwhile I will sum-up our discussion about "1V AC box + resistor":
While measuring 1V AC voltage coming out of the box with voltmeter/scope, we cannot discern - source is transformer, piezo device or just AC generator powered by chemical battery (we agreed that electrons are the same long ago in this thread). Kirchoff's circuit law (KVL) holds for AC voltage source + resistor *only* when AC voltage is generated by anything but transformer or other kind contraption ruled by Faraday's law. When we have transformer in a box, KVL does not hold anymore. To know - KVL holds or not, we have to look inside the box, otherwise we may be mistaken. This is what you are claiming? Anybody else agreeing?
This is exactly why the other "less scientific" definition of voltage (The one about how many electrons there are in one spot) is used in circuit analysis and pretty much everywhere else where you need to actually calculate something.
QuoteMy way of looking at this box+resistor debate: if black box is able to produce AC 1V alone, I name it EMF source - disregarding it is transformer or just DC-fed AC generator. If I connect resistor, I close the loop, AC 1mA current is flowing and integral E.dl around the loop is zero. There is no magic, just quite simple logic and law of conservation of energy. Do you agree?
No. This is the root of your problem in understanding Faraday. You start with the assumption that integral of E.dl around a loop is zero to prove your thesis that integral of E.dl around the loop is zero.
KVL does not work anymore, and that's the point in saying that Kirchhoff is for the birds.
In short, the loop, the way it is, is unlumpable.
Lumpable means that I can measure the same voltage regardless of the position of the voltmeters.
What we have is a loop antenna. There is a reason why loop antennas are connected by two-wire transmission lines.
The specified conductor length of 1000000 meters is not ideal.
Conductor length should be between 121,250 and 242,500 meters at the specified frequency of 0.0003 MHz.
Why would you do that? The changing magnetic field produces an electric field. The electric field lines are circles around the magnetic field as shown in post #16:
https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/msg2003414/#msg2003414 (https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/msg2003414/#msg2003414)
If you have electric field lines that form a loop, as in this case, you have a nonconservative field.
So you don't have two voltmeters connected to same point showing different voltages? This is what happens in the experiment. Or are we supposed to imagine that it doesn't?
The two voltmeters will only measure the same voltage if the voltmeters and their connecting wires are outside the field region or somehow shielded or arranged so that the field does not affect the measurement. Fine, but that is not this experiment. This experiment is set up to demonstrate Faraday's law and non conservative fields.
You seem to be claiming that a voltmeter only measures an electric field caused by separation of charges. For example, you have to move charges on the gate of the input FET of the voltmeter to make it read a voltage, I guess is what you mean.
But the voltmeter can't tell you what separated the charges. It could be a battery, it could be a solar cell, it could be a thermocouple, it could be a hall effect device, it could be a loop of wire surrounding a changing magnetic flux, or it could be a loop of wire rotating in a static magnetic field, to name a few possibilities. The voltmeter cannot distinguish the charge separation caused by the electrostatic scalar potential from the charge separation caused by all the different other types.
In this case, the wires connecting the voltmeter are passing through a region that has a non-zero electric field. That electric field, interacting with the charge in the wire, will give you a different reading on the voltmeter depending on the path the wires take through that field.
*You* have problem, not me. You say that resistor with voltage drop have zero E field inside. That means that integral E.dl over it is zero meaning that it does not have voltage drop on it! It's paradox, don't you see?
What?! TL;DR. You did not even answer.
I will try again.
1) Does KVL hold when inside box is DC battery? 2) Does KVL hold when inside box is battery-powered AC generator? 3) Does KVL hold when inside box is piezo-based 1V AC voltage generator? 4) Does KVL hold when inside box is transformer?
This is exactly why the other "less scientific" definition of voltage (The one about how many electrons there are in one spot) is used in circuit analysis and pretty much everywhere else where you need to actually calculate something.
You keep talking of that as if it were a different physical quantity, measured in different units. It's not. The 'scalar potential' that is part of the (V, A) pair is just the path integral of the conservative part of the total electric field.
It's as if you decomposed a mathematical function into its odd and even parts and than claimed that the odd part is a different, 'less mathematic' definition of function.
You can easily see where that decomposition comes from by writing Faraday's law (use dS for the differential element of area to avoid confusion with the vector potential A, and use E_total instead of E to highlight that it is the resulting field, superposition of coulombian and induced fields). Then express B in terms of the vector potential A, turn the surface integral on the right into a path integral along the surface contour using Stokes (or "the rotor's") theorem. Now take the integral on the right to the left, changing sign. Bring everything inside the same path integral. You are left with a field whose circulation along a closed path is always zero.
Hey, that's a conservative field! Well of course, you have stripped the induced - non conservative - part from the total field.
Congratulations, it can be very useful, but it's only half of the story.
I will come back to this post with formulas and drawings when I will be able to scan.
You say that resistor with voltage drop have zero E field inside. That means that integral E.dl over it is zero meaning that it does not have voltage drop on it! It's paradox, don't you see?
Indeed. But I never said that the resistor has zero E-field inside. I said that the circulation of the conservative part of the E field is zero.
The conservative part of the E field is stronger in the copperas well. It has to be in order to cancel the induced part.
QuoteI will try again.
1) Does KVL hold when inside box is DC battery? 2) Does KVL hold when inside box is battery-powered AC generator? 3) Does KVL hold when inside box is piezo-based 1V AC voltage generator? 4) Does KVL hold when inside box is transformer?
1) yes, outside and inside
2) it depends. Does the generator have a time-varying B field inside ? Is so and if the flux is neatly tucked inside the box, then 'extended KVL' (which is Faraday under disguise) will appear to work outside, but won't work inside when you cross the flux-varying region.
3) I am not familiar with piezoelectric generators, but if there is no dphi/dt involved we probably can treat them as batteries.
4) 'new KVL' which is Faraday under disguise will appear to work outside and fail miserably inside if you attempt to cross the flux-varying region.
Did you just say that Dr.Lewin is mistaken? - Because he claims thatHe must have meant the total field.nonconservative field is zero inside copper coil (or secondary of transformer).
So, copper part have *only* nonconservative field, resulting voltage (integral E.dl) equals 1V. You agreed because you did not argue when I said that it is possible to measure 1V AC voltage on transformer secondary w/o resistor connected. (It would be dumb to argue anyway).No I do not agree and I have already explained how that can happen in one of my previous post (many pages back).
In our "box + resistor" case resistor is outside magnetic field of the transformer, so Faraday's law cannot do anything about it, so there cannot be nonconservative fields in form of EMF inside it.
According to logic above, sum of fields in copper and resistor, integral E_conservative.dl and integral E_nonconservative.dl is zero. [edit] At given time of observation obviously.
Fact that you even try to answer those questions is hilarious by it's own :) We agreed that for voltmeter it does not matter what's inside the box, it cannot sort out electrons - they were moved by class-AB amplifier, little monkeys or Mr.Faraday.
Did you just say that Dr.Lewin is mistaken? - Because he claims thatHe must have meant the total field.nonconservative field is zero inside copper coil (or secondary of transformer).
Keep in mind that the left side of Faraday's equation, circulation of E.dl refers to the total field.
Of course it might happen that the conservative field be zero as well: if all fields are conservative, the conservative field is all you've got and in that case the conservative field will be zero inside a perfect conductor. It happens for example in electrostatics: point charge generates a conservative E-field, you place a piece of copper nearby, free charges on the copper surface redistribute to create a contribution that will erase the field inside the copper. So sum of conservative E field due to point charge plus conservative field due to free surface charge equals total conservative E field inside the conductor is zero. And I think it will work with batteries and a copper wire.
It's all about context.
Can you show where Lewin said that?
QuoteSo, copper part have *only* nonconservative field, resulting voltage (integral E.dl) equals 1V. You agreed because you did not argue when I said that it is possible to measure 1V AC voltage on transformer secondary w/o resistor connected. (It would be dumb to argue anyway).No I do not agree and I have already explained how that can happen in one of my previous post (many pages back).
QuoteIn our "box + resistor" case resistor is outside magnetic field of the transformer, so Faraday's law cannot do anything about it, so there cannot be nonconservative fields in form of EMF inside it.
I have to stop you there: as long as you stay outside you can pretend that the contribute of -dphi/dt are either 'battery-like' emf of 'resistor-like' voltage drops. But when you get inside the box - and you have to get inside the box to compute the path integral of the total E-field along the circuit's path, you have to surrender this delusion and come to terms with Faraday.
QuoteAccording to logic above, sum of fields in copper and resistor, integral E_conservative.dl and integral E_nonconservative.dl is zero. [edit] At given time of observation obviously.
The above logic is flawed because it does not keep into account the right hand side of Faraday's equations.
From the outside of a toroidal transformer it does not matter how I place my probes
If you start "Is Kirchhoff's Loop Rule for the Birds?" video at around 15:10, you will hear it.Did you just say that Dr.Lewin is mistaken? - Because he claims thatHe must have meant the total field.nonconservative field is zero inside copper coil (or secondary of transformer).
Keep in mind that the left side of Faraday's equation, circulation of E.dl refers to the total field.
--snip--
Can you show where Lewin said that?
QuoteLOL. From which alternate universe your physics come from? When I measure 1V on the transformer terminals, you claim that it is not 1V actually?QuoteSo, copper part have *only* nonconservative field, resulting voltage (integral E.dl) equals 1V. You agreed because you did not argue when I said that it is possible to measure 1V AC voltage on transformer secondary w/o resistor connected. (It would be dumb to argue anyway).
No I do not agree and I have already explained how that can happen in one of my previous post (many pages back).
Don't even say "Faraday" in area where there's no magnetic field!
If you start "Is Kirchhoff's Loop Rule for the Birds?" video at around 15:10, you will hear it.
What I hear is "electric field" and I agree: the total, resulting electric field in copper is negligible. Zero in a perfect conductor. As I have always said.
Where do you hear him saying that (in this particular circuit) the conservative electric field in copper is zero?
Other post[/url] of yours is unfortunately off-topic because it is not specified that there is Dr.Lewin's experiment in the box.
Other post[/url] of yours is unfortunately off-topic because it is not specified that there is Dr.Lewin's experiment in the box.
Oh! I didn't notice that the topic had suddenly become off-topic. My bad.
Other pos of yours is unfortunately off-topic because it is not specified that there is Dr.Lewin's experiment in the box. It was defined that box is magnetically shielded and there is no EMF induced in the wires coming out of the box.
To give things some better perspective i have put together a few images that graphically show the fields.
WTF is the keyboard combination that can make you lose the whole post??
This site does not have a draft saving function? I was copying a ***** line and all went poof!
The ****! What the ****** *****!!!
In the case of the field produced by a primary cylindrical coil here is the induced e field magnitude:
(https://i.ibb.co/1RMrvkz/screenshot-11.png)
here is plotted with direction in a plane perpendicular to the axis of the infinitely long primary coil (here represented by the orange ring):
(https://i.ibb.co/2t2d8JF/screenshot-10.png)
Seems perfectly defined (of course it is time-varying but we can express exactly how - this is snapshot frozen in time). The voltage, on the other hand...
I'll skip the part regarding that paper you mentioned back when we had this discussion and that kept using AREA in computing the emf for a single line.
We're going 'full field' now, so forget areas - welcome boundary conditions!
You are able to plot the induced field only when you specify the boundary condition set by the coil generating the field.
After all Maxwell's equations in their differential form are... partial differential equations and if you do not specify boundary and initial conditions, how can you choose the solutions that suits your problem among the infinitely many? In their integral form, since the are essentially integral relations between areas and boundaries you have to specify... well, you know what. Maybe there is some equivalence hidden in there?QuoteYou only need a closed loop when you want to use Faradays law to directly calculate the EMF voltage. It doesn't mean that you can't have EMF without a closed loop just because Faradays law uses a loop area, it just means you have to use other laws to calculate your EMF in those cases.
Except the EMF is only half of the story.
When you put the secondary coil in, the charges in the conductors will rearrange to produce the coloumbian field and the resulting field depends on how you close (or do not close) the loop. After all E_total has the same direction of j. You can end up with a total E that is opposed to E_induced (it helps using a finite albeit big value for sigma). I had written something else in the lost post but **** it! Anyway I still need to scan my drawings so...
And so, what is the true voltage?
Because it seems to me that in your coloring analysis you skipped the Mabilde-McDonald voltage right away and went on calling "true voltage" other voltages.
If I understand correctly, what you call "Charge density" is the voltage definable as potential difference that is associated with the coloumbian aka conservative part of the total field. Why is not that the true voltage?
I can't call the charge density approach true voltage because that is not how voltage is formally defined. But this is the voltage that all voltmeters detect and show as a result and it is never undefined so i tend to use this so called "effective voltage" or "conservative voltage" or "columbian voltage" or whatever you want to call it, just because its more useful to work with, while not breaking any of Faradays or Maxwells math.
In fact, when you bring a voltmeter inside the ring, you can measure any voltage you want between -0.1V and +0.9V
Quote from: BerniYeah forum web software has not advanced much at all in the last 20 years.Well, some web software has advanced. Stack Exchange for example, saves the drafts, upload images directly, has a nice TeX editor... Too bad they pissed me off with their censorship attitude. But, never mind.
I am a bit at a loss, here. I thought you were looking for the true one and only voltage, the one that has is so uniquely defined that it can be expressed as a potential difference, independent of path. And yet you say that potential is undefined?
Are you referring only to the possibility to run more than one time around the core (in which case, we could overlook it, limiting ourselves to a full circle at most) or is this a more fundamental lack of uniqueness?
Because the way you used colors makes me believe you are selecting a particular class of paths to represent your color coded voltages, namely paths along the circle. You fix 0 at one node (A, IIRC) and then compute the path integral along the circle from A to another point P on the circle. Do we agree that this does not exclude the possibility that the voltage from A to P depends on the path?
Which one of the many voltages you have shown is the path-independent one?
(My guess is that it has to be the first one, the conservative one you called "charge density". And yet you say
Which seems to me an admission that... the true voltage is path dependent, as Lewin has always said. But let's forget about this for the moment. The part I am more interested in is the followingQuoteI can't call the charge density approach true voltage because that is not how voltage is formally defined. But this is the voltage that all voltmeters detect and show as a result and it is never undefined so i tend to use this so called "effective voltage" or "conservative voltage" or "columbian voltage" or whatever you want to call it, just because its more useful to work with, while not breaking any of Faradays or Maxwells math.
So to be clear, is this the voltage Mabilde is measuring? The one that Kirchhoffian call the 'true and one voltage'? You just decided to call it with another name (not a problem, we just need to be clear) but can you clarify that this is the case and that what you called "Charge Density" in the picture and call now "effective, conservative, coloumbian voltage" is the Mabilde-McDonald voltage?
Before addressing the meaning of said voltage, let me say that there is one problem with you statement above. You wrote that "that is the voltage that all voltmeters detect and show as a result". I am afraid you are mistaken.
To show the Mabilde-McDonald voltage you need a special measurement setup, consisting in a careful choice of your probes' path. The voltage all voltmeters detect is the one with the operational definition of path integral of E. The one that depends on the path of your probes when there is a changing magnetic field. In fact, when you bring a voltmeter inside the ring, you can measure any voltage you want between -0.1V and +0.9V and that is what the voltmeter show. Even outside you have two different values depending on how you place the probes around the core.
So, no. The 'effective, conservative, coloumbian voltage' is not the voltage that all voltmeters detect and show as a result. You did the experiment yourself!
But I think I know where you got that idea.
I will address that in a separate post, along with my answer to this
QuoteAlright then lets hear how you think one should calculate the charge density on the ends of a open wire in a changing magnetic field.
EDIT: fixed sentence I had left without conclusion.
Stack Exchange for example, saves the drafts, upload images directly, has a nice TeX editor... Too bad they pissed me off with their censorship attitude. But, never mind.Yeah true, but the strict moderation is what makes stack exchange so useful when you just want a quick, concise and correct answer to a technical question. The best answers float up to the top and some answers actually have a significant amount of effort behind them.
Well? How do we calculate it then? Or is there no need to calculate it because it's zero perhaps?
Suppose I put my electron in, with particular initial conditions (like velocity in a particular direction starting from A) and that I have recorded its trajectory from A to B. Would you agree in calling the voltage computed along that path the most meaningful voltage for this particular experiment?
You can read +1V and -1V as well - if you short probe leads that go around solenoid. Some academic scientists and their worshippers may say "Look! I discovered that voltage is path-dependent" while actual "discovery" is just electromagnetic induction.
Oh, come on. I thought we were past that.
Voltage in non-conservative E-field IS path-dependent. This is not even up for discussion.
Nah, the problem is twofold: first, science is not and should not be democratic - so the 'most voted answer is the best' is not necessarily true and the mechanism is flawed from the start. While it might work fine for some 90% of the content, when it comes to specialized stuff, it breaks miserably. This flaw is exacerbated by the editing power that one can exert even if he/she has no clue of what is being discussed (meaning the so called 'expert' in one branch might only have an approximate and sometimes erroneous knowledge of other branches). Imagine if you and ogden had the power to close this discussion because it's crystal clear that this is just a probing error (and you have more yellow square than me and MHz). Or to look if from the other side, if Mhz and I had the power to shut up Kirchhoffians by editing and removing their posts (and once they are removed, if the site has enough traffic there won't be enough people to notice or even care to reopen them).NobodyMany readers in this blog would not have discovered the surprising role of surface charge in keeping the current within a conductor (I will get to that when I will have completed my drawings and scans).
I was happy with the way Physics SE is run: there is highly competent people making the selection there. Not so much in EE. Waste my time once, shame on you. Waste my time twice...
Scientific populism will be a problem a few years ahead.
But enough digressing.
QuoteWell? How do we calculate it then? Or is there no need to calculate it because it's zero perhaps?
We use Maxwell's equations. What else?
Zero? With an abrupt discontinuity at the ends and an induced field of known geometry? What makes you think that?
It is zero in a closed isotropic circular conducting torus perfectly aligned with the circular induced field. But even then, my guts say you just have to move it off axis to see charge pile up on the 'lateral' surface (well, is there any other surface on a torus?). And if you place portion of different resistance, you will certainly see charge pile up at the surface of separation.
I've found plenty of literature supporting my point of view. I need a little bit of time to sift through the best works and select a few images. Keep your popcorns in a warm place, I'm almost done with my flu.
edit: nobody was a truly bold statement. In my defense, it's all Jackson's fault. I'll explain later
Nah, the problem is twofold: first, science is not and should not be democratic - so the 'most voted answer is the best' is not necessarily true and the mechanism is flawed from the start. While it might work fine for some 90% of the content, when it comes to specialized stuff, it breaks miserably. This flaw is exacerbated by the editing power that one can exert even if he/she has no clue of what is being discussed (meaning the so called 'expert' in one branch might only have an approximate and sometimes erroneous knowledge of other branches). Imagine if you and ogden had the power to close this discussion because it's crystal clear that this is just a probing error (and you have more yellow square than me and MHz). Or to look if from the other side, if Mhz and I had the power to shut up Kirchhoffians by editing and removing their posts (and once they are removed, if the site has enough traffic there won't be enough people to notice or even care to reopen them).NobodyMany readers in this blog would not have discovered the surprising role of surface charge in keeping the current within a conductor (I will get to that when I will have completed my drawings and scans).
But enough digressing.
Keep your popcorns in a warm place, I'm almost done with my flu.
If probe tips are shorted meaning voltage is 0V but I get 1V indication, I cannot call it meaningful by any stretch of imagination.
If voltage indication changes depending on how you manipulate with probe wires - you cannot trust your measurements not to mention make big scientific thing out of it. |O
I already said that and can repeat: "voltmeter reading (but not actual voltage in the connection point) depends on the path of test leads, especially if they are placed in the varying magnetic flux."
If probe tips are shorted meaning voltage is 0V but I get 1V indication, I cannot call it meaningful by any stretch of imagination.
Maybe nature wants to tell you something you are ignoring.
Well, Michael Faraday, a scientist, had the same problem that you do way back in 1831.
If Kirchhoff always held, you couldn't have the modern world and we would be able to have this very conversation. Learn to live with that.
LOL. Have to repeat that you are "arguing (https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/msg1979633/#msg1979633) against the nonexistent strawman who is apparently suggesting that Farady's law is incorrect, and Kirchoffs is always correct", like broken record.
I might have missed a few but these are the ones i remember right now. Any disagreement on these?
To make things easier i will summarize most of my claims in a list:
1)
...
19)
I might have missed a few but these are the ones i remember right now. Any disagreement on these?
I might have missed a few but these are the ones i remember right now. Any disagreement on these?
I would add definition of voltage to 2 ). Version "True voltage is integral of all forces acting on a electrons along the path" is kinda tricky because some may think that electron(s) shall be carried all the way along the path for voltage to appear, which is untrue. IMHO worth to mention more straightforward "the work needed per unit of charge to move a test charge between the two points". It also "connects" better to volt = joule/coulomb equation.
I disagree with 8 ) because both "all forces on electrons along the path" and "work per unit of charge" voltage definition variants allows voltage to be present on terminals of zero resistance "open lengths of wire" or inductor. After all there's well-known equation: V = L(di/dt)
Kinda offtopic or maybe not. -How special relativity is related to this discussion:
p.s. How to (easily) avoid this gigantic thumbnail appearing when I include URL to YT video?
...you keep saying wires always have no voltage across them (apart from restive drop). So you are now saying that wires can have voltage across them?
You can have voltage at the terminals, with zero field and zero voltage inside the secondary. (EDIT: of course in case sigma = infinity, so what I called copper has to be thought as a perfect conductor - otherwise, we would see minimal resistive losses and a negligible E complying with j = sigma E).
These are just the essential pictures of a long story that starts with electrostatics, so consider this a sneak preview (and please do not mind too much at signs, they were not my priority here)
Consider a single loop secondary and a closed IMAGINARY, MATHEMATICAL closed path going through the copper and joining the terminals. Like this
(https://i.ibb.co/QdgY9Hs/screenshot.png)
How does a transformer work? By applying Faraday. Not Kirchhoff, Faraday. I have a closed path, it defines an area. Let's do it!
(https://i.ibb.co/WWbdXNT/screenshot-3.png)
Ok, nice formula, how do I fit it into my circuit?
Let's decompose the closed path into two partial open paths and see what we can get out of that:
(https://i.ibb.co/qBhYxxc/screenshot-4.png)
We've got this:
(https://i.ibb.co/hVCCqHC/screenshot-5.png)
and the notion that you can have zero field and zero voltage inside the wire of the secondary coil, while having voltage at the terminals. Try to explain this with KVL.
For 8 ) Yes V = L(di/dt) is sort of a "patch" to make voltage appear on the terminals of transformers when using the textbook definition of voltage. It assumes a lumped inductor and places this voltage across its terminals even tho the voltage inside the inductor is ether zero, the resistive loss, or undefined. So by moving a nanometer into the transformer terminals you get the 0V solution but the moment you step on the edge of a transformer terminal this "patch formula" comes into effect and suddenly you have lots of voltage.
For 8 ) Yes V = L(di/dt) is sort of a "patch" to make voltage appear on the terminals of transformers when using the textbook definition of voltage. It assumes a lumped inductor and places this voltage across its terminals even tho the voltage inside the inductor is ether zero, the resistive loss, or undefined. So by moving a nanometer into the transformer terminals you get the 0V solution but the moment you step on the edge of a transformer terminal this "patch formula" comes into effect and suddenly you have lots of voltage.
Let's put aside L(di/dt) which is not "patch" at all, but pay attention to what happens with electrons, thus charge in the coil during flux change. Charge is pushed to the one end of the coil. I can't see how resulting voltage on the terminals could be zero.
When you have a wire in a changing magnetic field that field can induce the non conservative E field along it. Because the electrons in a wire are free to move they start marching in the direction that field is pushing them. As a result they end up bunched up at one end of the wire. But when electrons are bunched up like that they create there own E field. This field opposes the magnetically induced E field and the electrons keep marching along until they are creating an electrostatic E field that exactly opposes the magnetically induced one. Now all the fields around the electrons sum up to zero so they stay still in there cozy equilibrium point.
So now if you take the formal definition of voltage (Work needed to move a unit of charge along a path) you will find that zero force is needed to move an electron along the wire because they is no force acting against you. As such by the formal definition of voltage there is 0V along the wire.
If you connect a load to the terminals of this coil then the voltage becomes undefined because you get a different result if you travel between the terminals along the path going trough the coil and a different result if you traverse the path by going trough the load.
More electrons bunched at the one end than another equals potential difference. That "cozy equillibrium point" happens when capacitor connected to wire loop is finished charging. You may want to say "there's no capacitor" - read my comments below.
Moving electrons to one end of the wire will create opposing magnetic field, opposing force. This means that to move electron, nonzero work shall be done. So there's your definition of voltage that predicts voltage.
As wire loop can't be infinitely small (area enclosed by the loop shall be > 0), it will be some kind of capacitor as well - you like it or not. So there's your load - capacitor that becomes charged. When magnetic field does not change anymore, this "parasitic capacitor" immediately discharges through low resistance of the wire.
I might have missed a few but these are the ones i remember right now. Any disagreement on these?
I would add definition of voltage to 2 ). Version "True voltage is integral of all forces acting on a electrons along the path" is kinda tricky because some may think that electron(s) shall be carried all the way along the path for voltage to appear, which is untrue. IMHO worth to mention more straightforward "the work needed per unit of charge to move a test charge between the two points". It also "connects" better to volt = joule/coulomb equation.
What do you see?
Or, better yet: what do you NOT see?
There are no voltmeters.
There are no probes.
There is no spoon.
And yet, the voltage between A and B can have two different values.
If you are right - then why there is voltage on transformer terminals?
Some academic scientists and their worshippers may say "Look! I discovered that voltage is path-dependent" while actual "discovery" is just electromagnetic induction."
If you are right - then why there is voltage on transformer terminals?
The field outside will not be zero, though.
And yet, the voltage between A and B can have two different values.
I have to agree with Ogden. Who are you actually arguing with?
To make things easier i will summarize most of my claims in a list:
1) There are indeed two voltages present at the measured points in Dr. Lewins experiment when using the formal textbook definition of voltage.
[snip]
9) Lengths of wire connecting the voltmeter to the probing points are part of the circuit and need to be analyzed along with the rest of the circuit. These wires transfer the voltage from the probing points to the voltmeter terminals where it is actually measured. If it is found that these wires generate a voltage that affects the voltmeters reading then this voltage must be subtracted out to get the voltage at the probe points. Failure to realize this, correct it, or compensate for it is considered as "bad probing".
10) Changing the path of the probe wires in Dr. Lewins circuit does change the voltmeter reading due to changing the charge density present on the voltmeter terminals. However when doing correct probing as mentioned above the result of the voltage at the probing points it always the same, regardless of wire path or voltmeter location (The effect is always substracted out).
11) Kirchhoffs circuit laws always work in circuit mesh models where all voltages use the "effective voltage" definition
12) Kirchhoffs cirucit laws can not be directly applied to just any real life circuit with the assumption of ideal wires, especially when high frequency AC signals are involved or significant magnetic effects are present
13) Kirchoffs voltage law does not contain an intergal of E as Dr. Lewin shows. Its actually a algebraic sum of all voltages on components and as such can only be used on a lumped model.
14) Kirchoffs cirucit laws do not go against Faradays law or Maxwells equations. All three can exist without conflict. Faradays law and KVL describe two different things and as such are not mutually exclusive.
15) Kirchoffs citucit laws have nothing to do with Maxwells equations, but they are used together whenever circuit analysis is used on reactive components such as inductors or capacitors.
16) The circuit from Dr. Lewins experiment can easily be lump modeled using multiple coupled inductors to represent wires. As such all common methods of circuit analysis can be applied to it including KVL to get results matching the real physical experiment
I might have missed a few but these are the ones i remember right now. Any disagreement on these?
And yet, the voltage between A and B can have two different values.At the same exact time?
Maybe you have to take into account the magnetic field generated by the flowing current through the wire...
The "correct probing" is a technique to avoid UNWANTED induction. But Lewin's experiment is exactly to show how voltage is dependent on the path under induction. So the voltage induced by the probes is PART of the experiment. You cannot subtract it out!
If you set up an experiment and employ a probing technique to suppress the very effect you are trying to demonstrate, you are on dope.
Aw, man! Don't do that. What do you think an integral is? You clearly have no idea that integrating the electric field along a path of lumped components will result exactly in the algebraic sum of all voltages on the components.
For the record, Richard Feynman and others use the line integral with lumped circuits to demonstrate Kirchhoff's law.
If they describe two different things, they are mutually exclusive.
Kirchhoff's law can be deduced from Maxwell's equations. This is classic electromagnetism.
No circuit under varying magnetic fields can be lumped modeled. Please read the Feynman lectures recommended by Mehdi.
We are not here to reach an agreement. We are here to ascertain the truths of electromagnetism.
What probe wires???
There are no probes wires in the computation of the path integrals I've shown above.
The two different values we get, for the two possibile path along the circuit, are the result of induction. But that's how the system is. If you remove the induced part of the field, you are analyzing a different (unrealistic) system.
It's as if you subtracted the field generated by the point charge near a piece of copper to come to the conclusion that there is a nonzero field inside the metal (and then came up with tiny generators inside the metal) that produce the observed surface charge.
Now, do I get to beat Mehdi, like in old Iran? >:D
What would Jesus do?
Exactly it gets rid of unwanted effects such as the probe wires needing to follow a certain path, but it does not get rid of what you are measuring.
You still get the same result in Dr. Lewins experiment if you use the formal definition of voltage when subtracting out the probes. It just so happens that he set the probe wires in such a path that you need to subtract 0V to get the result. If you move the wires you get a diferent result on the voltmeters. Does that mean that the voltage across A and B has changed? No you just messed up your probing.
If you compensate out probing effects you can place both voltmeters on the left side in Dr. Lewins circuit and still get 2 different voltages as a result. If you do all your probe compensation math with textbook voltage you get two different values for voltage no matter where the voltmeters or the wires are.
If you use the "efective voltage" in the math to calculate the error voltage on the probes to subtract out you get the same result on both voltmeters no matter where they are. (Just like here you could just place one voltmeter in the middle for this error voltage to be 0V and thus make no need to compensate it out)
Correct probing practices don't break Dr. Lewins two voltages across A and B experiment, but given that the path the probe wires take in Dr. Lewins physical experiment is important it should be said why the probe wires take the path they do. This particular path requires no compensation of probe error for what he is trying to measure, all other paths do.
Well in the lecture where he talks about it he uses the summa operator:
http://www.feynmanlectures.caltech.edu/II_22.html#Ch22-S3 (http://www.feynmanlectures.caltech.edu/II_22.html#Ch22-S3)
He also explains why analyzing circuits as lumped is a good idea in the section above the one linked.
They would be mutually exclusive if they would explain the SAME thing as being two different things.
Kirchhoffs circuit laws describe voltage and current relationships in circuit meshes. Maxwells equations describe the relationships of electromagnetic fields in our universe.
You certainly can, here is how: https://physics.stackexchange.com/questions/102458/how-can-kvl-kcl-be-derived-from-maxwell-equations (https://physics.stackexchange.com/questions/102458/how-can-kvl-kcl-be-derived-from-maxwell-equations)
However as you can see the equation you get as a result looks rather messy. This is sort of the physical world incarnation of Kirchhoffs law, but it does work with magnetic fields present, since the Maxwells equations that it came from also work fine with magnetic fields present.
Kirchhoff only stays so beautifully simple when you keep it within circuit meshes where it was meant to be used. Hence why it is so useful there.
I certainly agree for cases when the formal definition of voltage is used.
Or in the case that you are not allowed to use coupled inductors in circuit models, i sure hope that is not the case since that makes modeling transformers really tricky (And Dr. Lewins experimental circuit is just a glorified transformer)
Well in that case we can close the thread cause Maxwell beat us to the goal of ascertaining the truths of electromagnetism by a good 150 years.
Now, do I get to beat Mehdi, like in old Iran? >:DWell, the first crucifixion recorded by history was performed by the Persians in 522 a.C. So I guess Jesus may be a little bit furious as of now.
What would Jesus do?
Maybe we should set for 100 lashes with a wet noodle.
Cool! That's what I'm trying to do since 28 November when I told ogden to get better education (and I was subsequently called a troll).
You think you are not worthy of this title? Look for yourself how many times you managed to insult Berni in single post! You were bitterly arrogant against him through most of this discussion, yet he never pushed back
Arguing about unwanted and wanted fields... putting the 'P' in PhD.
I side with Mehdi on this.
The fields are effecting the probes, the only reason why the voltage changes is due to how the probe wires are affected by the probes. In such a way the laws are put in place, we talk of an ideal circuit.
If I was to make the same mistake while trying to measure a current sensor's voltage while wrapping the wires around the probe, I'd be laughed out of the room.
EDIT: Bernie, it's Sredni, not Sredini.
I am Sredni Vashtar the beautiful.
My thoughts are red thoughts
and my teeth are white.
My enemies call for peace,
but I bring them death.
So try not to piss me off, uh? :D
The real question is: would it measure the same in space, or indeed, Mars?
I mean the Earth is just a rock with nothing on it. Those rocks in space however, are the Future. We better figure out how to measure voltages there.
And yet, the voltage between A and B can have two different values.At the same exact time?
Yep. That's a snapshot at a given time.
The field will oscillate going one way, then the other, at - I do not remember exactly, maybe... 300 Hz?
At any rate, well within the limit of quasi static electrodynamics.QuoteMaybe you have to take into account the magnetic field generated by the flowing current through the wire...
Nope, self-inductance is negligible, and there are no retardation effects.
The same two points, at the same moment in time, can have different voltages between them.
And there are no voltmeters, no probes, no measurement errors.
That's just the way it is.
As for there being two forms of Kirchhoffs law:
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=618160;image)
Its the similar as the classical kinematics equation we all know from physics:
d=s*t
This equation is WRONG! It only works in a universe where the speed of light is infinite or in one where space and time are not related to each other in the form of a spacetime field. So is that for the birds too?
But the thing is that at any reasonable speeds we might encounter on earth the error in the result due to ignoring special relativity is pretty much in the parts per million or even smaller. So we use it anyway because it gives results that are still within margin of error, yet its much easier and faster to work with. In fact most physics equations we see in highschool only work in this fictional universe with infinite, speed of light, no atmosphere or drag and spherical cows. Yet a lot of these cut down formulas are still close enough to the real deal to be perfectly usable. Circuit meshes are the same sort of thing, not quite real but real enough for what they are supposed to do.
If you are going to use the classical simple form of KVL use it in circuit meshes where it indeed always works. If you want your circuit mesh to behave like the real circuit in the universe we live in then also use proper circuit modeling methods (where wires are modeled as having inductance). If you don't want to do that then don't just directly slap on KVL and expect it to work every time.
Instead you can use the version of KVL that is derived from Maxwell equations in the physical world, since that does work. Calculate it however you want, just don't carelessly mix formulas from our universe and formulas from circuit meshes. A lot of the times they work fine, but not always (As Dr. Lewin clearly demonstrates)
If you can't handle abstraction then just ignore circuit meshes and focus on pure Maxwells equations instead.
I can make sense of Dr. Lewins circuit both in the form of fields and in the form of a circuit mesh model. Both work just fine and give identical results. If you can't make sense of the circuit using a mesh model then try to learn how, otherwise don't complain about it being wrong just because you don't seam to understand it. I don't want to come across rude or anything, but any answer to why its wrong to mesh model this circuit is along the lines of "It can't be done because i said so" rather than getting an explanation why i am getting the right results out of my mesh model despite it being supposedly wrong for some mysterious reason.
Yes it looks like that when used in cirucit meshes. It has the extra voltage in it when you try to derive a "KVL like" equation from Maxwells equations. It has to be there otherwise there is a mistake in the process or Maxwells equations are wrong (And that's highly unlikely)
Unfortunately that is not Kirhchhoff's law. That is Kirchhoff's law.
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=619306;image)
And it is not difficult to see why.
Let's get back to the infamous Lewin's circuit. Kirchhoff says that all voltages around a circuit add up to zero. So I'm going to do exactly what he says. I will "walk" around the circuit with my voltmeter. Since "bad probing" would give me the wrong results and I would probably be laughed out of the room, I'm taking the proper precautions not to allow any stinking varying magnetic field to induce unwanted voltages on my probes. So, here we go.
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=619312;image)
So far so good. As an added precaution, I will measure the voltage across the wire, just to make sure it's what I expect.
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=619318;image)
And, bingo! Zero volts. No wonder. The wire is a dead short. Now it's time for the other resistor.
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=619324;image)
Notice that I'm maintaining the polarity of the meter coherent with the anticlockwise path that I chose. Now, let's check the voltage across the other piece of wire and add up the voltages.
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=619330;image)
Surprise! They do not add up to zero.
For Kirchhoff to hold there should be a V5 somewhere measuring exactly -1V. But I checked every corner of this circuit and didn't find any other voltage than the four I measured.
So, either Kirchhoff is a liar, or didn't see it coming. I prefer to believe in the second hypothesis.
But you are going to say, Aha! Gotcha! The loop is nothing more than the secondary of a transformer. But where exactly is that generator in the circuit? My measurements show that this generator is nowhere to be found.
So the logic conclusion is that voltages do not necessarily obey the observation made by Kirchhoff, petrified in his laws. There must be another phenomenon that, when present, brakes those laws.
From the point of view of Einstein's relativity, yes, Newton is for the birds. You cling to Newton, you won't be able to predict what Einstein did. Newton reveals an even worse relationship to Einstein, than Kirchhoff to Maxwell. The speed of light can't be infinite in practice, as you said. While we can have a zero magnetic field.QuoteBut the thing is that at any reasonable speeds we might encounter on earth the error in the result due to ignoring special relativity is pretty much in the parts per million or even smaller. So we use it anyway because it gives results that are still within margin of error, yet its much easier and faster to work with. In fact most physics equations we see in highschool only work in this fictional universe with infinite, speed of light, no atmosphere or drag and spherical cows. Yet a lot of these cut down formulas are still close enough to the real deal to be perfectly usable. Circuit meshes are the same sort of thing, not quite real but real enough for what they are supposed to do.
Such approximations work fine because we live under a relatively low constant gravitational field. We would only notice something wrong at astronomical scale. In fact we did, already in the 19th century. And that's why we have relativity today.
However the electromagnetic force is 10³⁶ times stronger than gravity. Noticeable deviations from the approximations such as those that we do to deduce Kirchhoff can be noticeable at a scale of millimeters. So they must be taken care of with much more attention.
You're absolutely right. I can't handle the "abstraction". I must admit. So I humbly ask you a favor. Please, show me how to solve the circuit below using exclusively Kirchhoff.
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=619336;image)
Thank you in advance.
Its just a matter of perspective.
Keep in mind Maxwells equations are an just an abstraction of Quantum electrodynamics.
Can't do it using just Kirchhoff.
But even if there was no magnetic field you couldn't solve it using only Kirchhoffs circuit laws.
Id solve your particular circuit with numbers but the size of the loop area is not provided so a numeric result is not possible.
Yes. The perspective of those who study Maxwell for real and understand the physical phenomenon with which they're dealing, and those who don't.
Poor Feynman. Won the Nobel Prize for nothing.
You said you could calculate Lewin's circuit using Kirchhoff with the exclusion of Maxwell.
Didn't you say that Kirchhoff is an abstraction of Maxwell? Doesn't Kirchhoff hide the ugly underlying details of Maxwell? Why do you need them now? Isn't it because Kirchhoff is in fact a special case of Maxwell?
This is just yet another contradiction that shows that such claims are nothing but false.
Call it an abstraction or special case or whatever you want.
Whatever you say man. I just want to point out what "Engineering Electromagnetics" by Hyat and Buck, Seventh Edition, says in page 94:
"Equation (21) (Curl integral of E.dl=0) is therefore just a more general form of Kirchhoff's circuital law for voltages, more general in that we can apply it to any region where an electric field exists and we are not restricted to a conventional circuit composed of wires, resistances, and batteries. Equation (21) must be amended before we can apply it to time-varying fields. We shall take care of this in Chapter 10, and in Chapter 13 we will them be able to establish the general form of Kirchhoff's voltage law for circuits in which currents and voltages vary with time."
What probe wires???
There are no probes wires in the computation of the path integrals I've shown above.
The two different values we get, for the two possibile path along the circuit, are the result of induction. But that's how the system is. If you remove the induced part of the field, you are analyzing a different (unrealistic) system.
It's as if you subtracted the field generated by the point charge near a piece of copper to come to the conclusion that there is a nonzero field inside the metal (and then came up with tiny generators inside the metal) that produce the observed surface charge.
The ones that connect his oscilloscope to points A and B, since the BNC connector on a scope does not conveniently have the exact contact spacing to touch the two points of interest.
Im not saying that the two voltages result is due to the probe wires. I am trying to say that the path that the probe wires take is important.
If you take probing into account you can run the wires in any path you want and get the same result. Still two voltages across A and B.
Alright then. Lets assume the area is 10cm2. I just copy pasted my procedure and filled in numbers
1) Use Faradays law to get the induced voltage
...
2) Use Thevenins theorem to reduce the circuit to a single voltage source and resistor (Involves the use of series lumping to get there)
...
3) Use Ohms law to find the current flowing in this reduced cirucit
...
4) Use Kirchhoff current law to deduct this same current must flow trough all components (If there was a junction node there would be more work here) to find the current flowing on each resistor
...
5) Use Ohms law to turn the current on both resistors to the voltages on resistors.
...
There now voltages and current across all components are visible. The conditionality for all values is in the clockwise direction around the circuit diagram. This is pretty much what Dr. Lewin did on his whiteboard except it includes phase. What is so special about this?
Whatever you say man. I just want to point out what "Engineering Electromagnetics" by Hyat and Buck, Seventh Edition, says in page 94:
"Equation (21) (Curl integral of E.dl=0) is therefore just a more general form of Kirchhoff's circuital law for voltages, more general in that we can apply it to any region where an electric field exists and we are not restricted to a conventional circuit composed of wires, resistances, and batteries. Equation (21) must be amended before we can apply it to time-varying fields. We shall take care of this in Chapter 10, and in Chapter 13 we will them be able to establish the general form of Kirchhoff's voltage law for circuits in which currents and voltages vary with time."
Yep, it's talking about 'new' or 'extended' or 'amended' KVL that is used with lumped circuits.
But it's really Faraday and Lenz carrying around Kirchhoff's corpse.
https://i.ibb.co/bWNhLK8/screenshot-9.png
But this breaks as well when you try to apply a lumped circuit rule to a non-lumped circuit such as the Romer-Lewin ring.
You could simplify to:
1) Use Faraday's law to find the EMF in the loop.
2) Use ohms law to find the total current in the loop (I = Total EMF / total resistance).
3) Use ohms law to calculate the voltage drop across each resistor (V = IR).
Notice that you MUST use Faraday's law to solve this, and you do not use Kirchhoff's loop rule at all to solve it.
Doesn't that say something?
Aren't we talking here about Kirchhoff's circuital law for voltages? Are you aware of the generalization of Kirchhoff's circuital laws to systems other than linear electric systems? I can recommend you the book "Physical Networks" by Richard Sanford which explains how to apply KVL and KCL to other "circuits" with potential/flow properties. The book deals not only with electrical systems, but rotational, translational, and fluids-flow (as water in tanks) systems as well as combinations of all of them via "transformers". Although not covered in the book, the same rules (as in KCL and KVL) apply to thermal and magnetic circuits as well.
The problem you are having with the so called Romer-Lewin ring is that you are decoupling a circuit that can not be decoupled. In the so called Romer-Lewin ring the inductor generating the time varying field is part of the circuit and must be included in the solution via the standard equations of transformers. Then KVL "magically" works as shown by Electroboom. I don't know man, maybe Richard Feynman was right when he said in one of his lectures on physics (Lecture 25: Linear Systems And Review, at about minute 25:40):
"The difference between a physicist and an electrical engineer is not the difference in anything he knows, except one fact... not the mathematical knowledge or anything else except just one extra fact the physicist knows and that is: electrical systems are not the only linear systems in the world. All you have the same equations the same problems exactly in electrical engineering and you have in all the rest of physics. And all the difference between a physicist and electrical engineer is that the physicist knows the same equations apply to another circumstances and he gets in [obviously] and the electrical engineer looks puzzled, and that so is simply why they hired a physicist... I know that but that wasn't an electrical circuit..."
Aren't we talking here about Kirchhoff's circuital law for voltages? Are you aware of the generalization of Kirchhoff's circuital laws to systems other than linear electric systems?
I can recommend you the book "Physical Networks" by Richard Sanford which explains how to apply KVL and KCL to other "circuits" with potential/flow properties. The book deals not only with electrical systems, but rotational, translational, and fluids-flow (as water in tanks) systems as well as combinations of all of them via "transformers". Although not covered in the book, the same rules (as in KCL and KVL) apply to thermal and magnetic circuits as well.
The problem you are having with the so called Romer-Lewin ring is that you are decoupling a circuit that can not be decoupled. In the so called Romer-Lewin ring the inductor generating the time varying field is part of the circuit
and must be included in the solution via the standard equations of transformers. Then KVL "magically" works as shown by Electroboom.
The problem you are having with the so called Romer-Lewin ring is that you are decoupling a circuit that can not be decoupled. In the so called Romer-Lewin ring the inductor generating the time varying field is part of the circuit and must be included in the solution via the standard equations of transformers.
Then KVL "magically" works as shown by Electroboom.
I don't know man, maybe Richard Feynman was right when he said in one of his lectures on physics (Lecture 25: Linear Systems And Review, at about minute 25:40):
"You are decoupling a circuit that cannot be decoupled." HAHAHAHAHA!
The only magical power we have seen Mehdi show, up to now, is the power of attracting those who are lazy enough to understand electromagnetism and need a pseudo-theory to justify their ignorance.
Everybody likes to quote Feynman, but no one has the guts to study the subject-matter of his lectures.
The problem is that if you do that you are lumping the unlumpable.
Tho to be honest i never seen physicists use circuit schematics to describe anything other than electrical things. It seams to me its more of an electrical engineering thing where engineers have no clue about some random physical system, so they do "when you have hammer every problem looks like a nail" and mold the problem to look like a circuit since that's the one thing they do know how to deal with easily.
At least i never saw this "circuit meshes are not just for electrons" concept even mentioned any of my physics classes, while i have used the trick extensively in a lot of engineering classes to make sense of magnetic circuits, water flow, heat flow etc.. and to actually calculate stuff with it.
Ad hominem... that will prove you right.
KVL is a pseudo-theory?
Do you know KVL can be derived from Maxwell Equations?
So electrical engineers don't study linear circuits now! Wow, that must be a new curriculum!
By applying the same logic an inductor is unlumpable... therefore we can not use KVL in circuit that includes an inductor!?
I don't know about electrical engineers, but those who don't study Maxwell don't understand electromagnetism.
And you're the proof of that. Since you haven't read the Feynman's lectures recommended by Mehdi himself, you simply don't understand why an inductor is a lumped component and why Lewin's circuit is not solvable by KVL.
The problem is that if you do that you are lumping the unlumpable.By applying the same logic an inductor is unlumpable... therefore we can not use KVL in circuit that includes an inductor!?
Read carefully Feyman's lecture Vol. 2, Chapter 22 (the same you've already linked before), sections 22-1, 22-2 and 22-3 at least. If you do not manage to see the answer there, we'll be happy to help.
Read carefully Feyman's lecture Vol. 2, Chapter 22 (the same you've already linked before), sections 22-1, 22-2 and 22-3 at least. If you do not manage to see the answer there, we'll be happy to help.
But did you also read the beginning of section 22-8 too?
Cool. Since I said at least 22-1, 22-2, 22-3, I'm pleased that you read the whole chapter and I hope that you've finally found why a section of wire in Dr. Lewins experiment can't be inductor lump modeled as a 1/4 fractional turn around a transformer and in what way it acts differently than a transformer.
Cool. Since I said at least 22-1, 22-2, 22-3, I'm pleased that you read the whole chapter and I hope that you've finally found why a section of wire in Dr. Lewins experiment can't be inductor lump modeled as a 1/4 fractional turn around a transformer and in what way it acts differently than a transformer.
I have quickly went trough it last year already because it is a very good explanation.
But what point in the lecture exactly does it say that this can't be done? Yes it does explain that when considering a lumped inductor all magnetic fields have to be contained inside it.
Cool. Since I said at least 22-1, 22-2, 22-3, I'm pleased that you read the whole chapter and I hope that you've finally found why a section of wire in Dr. Lewins experiment can't be inductor lump modeled as a 1/4 fractional turn around a transformer and in what way it acts differently than a transformer.
I have quickly went trough it last year already because it is a very good explanation.
But what point in the lecture exactly does it say that this can't be done? Yes it does explain that when considering a lumped inductor all magnetic fields have to be contained inside it. This is another way of saying that the inductors field should not affect anything else around it. Note that the inductor still has wires coming out that are in two different physical locations in order to give you two terminals, this means it can't be a fully closed loop inside the shielded "lumping" box. We still need extra wire outside the box to close it and connect it to for example a voltmeter. The diference between the wires inside the box and outside the box is just that the ones outside have no magnetic field around then and so no EMF. This is the exact same thing as getting rid of the shielding box but placing the wires to the voltmeter in such a path that they generate no EMF. So any piece of wire taking any path inside the shielded box can be considered an inductor (Doesn't have to be coiled up around a former or a core). And if we are careful not to interact the rest of the circuit then the shielding box can be removed and it behaves the same. So putting all of this together any length of superconducting wire can be considered a lumped inductor (tho care must be taken if its not shielded). Are any of my claims here false?
But Dr. Lewins experimental circuit is not laid out in such a way that other parts of the circuit would avoid the field. All sections of wire are enveloping the magnetic field and are so affected by it in the form of EMF. But if you look at a transformer it also has this feature common. There are multiple sections of wire enveloping a common magnetic field in the core. It would be really annoying if we couldn't apply circuit analysis to any circuit containing a transformer, so the inductor model was 'upgraded' to allow it to be friends with other inductors in the same field, this is explained in the section i mentioned:
http://www.feynmanlectures.caltech.edu/II_22.html#Ch22-S8 (http://www.feynmanlectures.caltech.edu/II_22.html#Ch22-S8)
This concept of mutual inductance allows transformers to be modeled with multiple inductors almost as easily as a single inductor. Notice that the mutual inductance value is separate from self inductance, this allows the proportion of the two to be adjusted to obtain any intensity of coupling you want. This is effectively saying how much of the flux the two coupled inductors are sharing (Its also what determines leakage inductance in transformers). Fractional turns in transformers are also possible because a length of wire might not necessarily enclose 100% of the flux in the core.
Putting it all together now. So since any length of wire can be considered an inductor and because these inductors around a common 'core' can be considered a transformer then this circuit could be considered a transformer with 4 secondary coils connected into a configuration with 2 resistors. If not, can you explain why?
Any electrical/electronics engineer will agree with you.
I have quickly went trough it last year already because it is a very good explanation.
But what point in the lecture exactly does it say that this can't be done?
This is the exact same thing as getting rid of the shielding box but placing the wires to the voltmeter in such a path that they generate no EMF.
[snip]
Are any of my claims here false?
Putting it all together now. So since any length of wire can be considered an inductor and because these inductors around a common 'core' can be considered a transformer then this circuit could be considered a transformer with 4 secondary coils connected into a configuration with 2 resistors. If not, can you explain why?
Any electrical/electronics engineer will agree with you.
Any electrical/electronics engineer without a clue about electromagnetism will agree with you.
TIFIFY.
I told you to read it carefully, not quickly.
Yes. There are. What generates the EMF is the varying magnetic field. Not the wires.
What the wires do is to nullify any electric field along their path. Just that.
With pleasure. Feynman explains mutual induction after he explains that an inductor is a lumped component.
An inductor can only be considered a lumped component if, and I quote, we assume that there is a negligible magnetic field in the external region near the terminals a and b.
There are no negligible magnetic fields near the "terminals" of your "inductors" in Lewin's circuit.
So, sorry, you can't lump model Lewin's circuit. It is impossible.
Any more questions?
That's how the wires react to the induced field.
The induced E field depends on the magnetic B field (rate of change) inside the component.
Oh, for the love of...
Try to draw your new 'equivalent' circuit. Then you should see how equivalent it is to the Romer-Lewin ring.
Try to draw the circuit, WITH THE VARYING B FIELD REGION, and see if you can manage to do what you proposed: "replace each section of wire with 1000 turns around the loop then putting it into a shielded box including the solenoid coil while leaving the resistors and voltmeters outside".
My bet is that you will end up with circuit (a).
PS
BTW, how do I embed images properly in this forum?
So since we are so bothered with how the magnetic field affects things other than wires ---
i get the feeling that you two understand Maxwell perfectly well but have some issues understanding circuit analysis and circuit modeling.
Ah alright that's what is bothering you, alright fine il do some drawing too.
By the way bsfeechannel two of your batteries are drawn backwards (Botton inner two)
So since we are so bothered with how the magnetic field affects things other than wires in the circuit lets fix that by putting the major wires into a shielded box.
This box has infinitesimally small holes to conveniently get out wires out of it and is made out of a superconducting material or a material with an infinite permeability. This makes it impossible for the field inside to escape, but because magnetic monopolies are not possible in our universe means that the upwards flux must close itself somewhere. A superconducting box would get eddy currents induced on the inside that produces this opposite downwards flux in the walls, or in the case of an infinite permeability box the field lines would just follow the path of least resistance along the inner surface of the box to flow back down.
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=630313;image)
For convenience i also added some voltmeters around the scene. I think all of you will agree with the readings they are showing. Notice that the rightmost voltmeter is showing zero because the sum magnetic field outside the box is zero (If it was showing anything else than we don't have an ideal shielding box).
So since the field is contained and the box contains nothing else but coupled inductors we can turn it into a ideal transformer and all the voltmeters still show the same readings (Follow each path and add it up if you don't believe me)
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=630319;image)
This shows that an ideal transformer can behave like the above circuit when it is in a box, something that shouldn't be surprising.
Okay but we don't actually have this magical ideal shielding box. So lets look at what would happen if the box was removed?
Well unsurprisingly the most inner voltmeters that used to show 0.1V and 0.9V would show the same value. The path trough them does not enclose any extra flux so there is no reason for them to show something different. This now completes the chain, the circuit behaves like a transformer even if we don't contain the fields.
Where things do get messed up is all other voltmeters. The magnetic field is now affecting all there probe wires and as a result affecting the voltmeter readings. If we wish to continue doing circuit analysis then the model has to be updated to give those wires correct coupled inductance too, after that the voltmeter readings from circuit analysis will once again match the real thing.
Any objections to this explanation?
And i still don't see what part of Maxwell i supposedly don't understand. All of this makes perfect sense to me from the point of view of Maxwell or from the point of view of mesh circuit analysis.
Where do the explanations above violate Maxwell?
Sorry if it sounds rude but i get the feeling that you two understand Maxwell perfectly well but have some issues understanding circuit analysis and circuit modeling.
Ah alright that's what is bothering you, alright fine il do some drawing too.
Ah alright that's what is bothering you, alright fine il do some drawing too.
I wonder when you realize that those guys do not have word "agree" in their vocabulary :D They are ready to disprove their own words - if it is you who is speaking ;)
By the way. Here is the real thing without the lumping box, in case someone still has some doubts.
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=630868;image)
I can't see where we are disproving ourselves. We are not claiming anything. We're consistently showing that the claim that Kirchhoff always hold is nothing but quackery.
I wonder when you realize that those guys do not have word "agree" in their vocabulary :D They are ready to disprove their own words - if it is you who is speaking ;)
We're consistently showing that the claim that Kirchhoff always hold is nothing but quackery.
By the way. Here is the real thing without the lumping box, in case someone still has some doubts.
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=630868;image)
Yep that's what it would show without the box.
Notice that the inner voltmeters still show 0.1V and 0.9V? Care to explain why they didn't change regardless of the shielding box being there while others did change?
I can't see where we are disproving ourselves. We are not claiming anything. We're consistently showing that the claim that Kirchhoff always hold is nothing but quackery.
It always holds in circuit meshes, not elsewhere. Typical word twisting as usual.
I wonder when you realize that those guys do not have word "agree" in their vocabulary :D They are ready to disprove their own words - if it is you who is speaking ;)QuoteYeah this has turned into a Maxwell versus Kirchhoff pissing contest 15 pages ago. But so far i have yet to see a good explanation why the two can't be both used provided you know how to use them rather than just slapping formulas on things without knowing what they actually do.
We're consistently showing that the claim that Kirchhoff always hold is nothing but quackery.
You have serious issues. Nobody claims that Kirchhoff always hold.
We're consistently showing that the claim that Kirchhoff always hold is nothing but quackery.
You have serious issues. Nobody claims that Kirchhoff always hold.
Ogden said that Mehdi is nobody. Duly noted.
Look up the word sarcasm in the dictionary.
Of course. Because the line integral along the path that includes them and the wires is exactly the same. In other words, the varying magnetic field that the meters and the wires are encircling is exactly the same. The magnetic field outside the closed path doesn't affect the EMF.
This is what Faraday discovered and Maxwell described mathematically. As simple as that. That's the way nature works. There's nothing we can do to change that. You have to accept it. Not because I'm tell you, but because every time you try to repeat this experiment, it will always work that way.
There is, of course, an explanation for the underlying phenomenon of induction, but it is not the topic of this thread.
QuoteI can't see where we are disproving ourselves. We are not claiming anything. We're consistently showing that the claim that Kirchhoff always hold is nothing but quackery.
It always holds in circuit meshes, not elsewhere. Typical word twisting as usual.
NOOOOOOOOOO. Kirchhoff doesn't always hold even for circuit meshes. The inductor itself is a proof of that.
If Kirchhoff always held you couldn't even have inductors, as the voltage inside an inductor, i.e. along the path of the wire, is zero and outside it is different from zero. How can that be?
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=631189;image)
You don't understand it because you didn't read Feynman carefully as I recommended you to. This explanation is there.
It's because Kirchhoff fails that we have inductors, generators, transformers, antennas, etc.
Thanks to your favorite deity, or the lack thereof, that Kirchhoff fails. The failure of Kirchhoff is the best thing that could happen to humankind. Every time Kirchhoff fails, the world smiles. (I think I'll create a t-shirt with those words.)
This is not a pissing contest between Maxwell and Kirchhoff. As Kirchhoff is a special case of Maxwell, the only thing we are trying to show you is exactly that.
Yes, so when you say they are exactly the same also means that you are saying this circuit exactly acts exactly the same as a ideal transformer.
If not, can you show in what way does it behave differently?
Have you ever did AC circuit analysis my hand? If you did then i would have assumed you would have less trouble understanding what an inductor is.
Sometimes circuit modeling even uses inductors where there are no magnetic effects involved (One such example is the common model of a quartz crystal). An inductor is simply U=L*di . If you want to have always zero voltage over it just give it 0H of inductance, but i don't think that's a particularly useful use case for an inductor model.
What exactly are you trying to prove with that diagram? We all know you can't just directly use Kirchhoffs circuit laws inside real world magnetic fields. Did anyone say you can?
Well yeah its a special case where circuit meshes (Where KVL is meant to be used) without realistically modeled wires happen to behave the same as a real world circuit.
Both Maxwell and Kirchhoff work just fine when used correctly. So why is it a problem that there are two ways to go about calculating electrical circuit behavior?
QuoteIf not, can you show in what way does it behave differently?
It behaves differently because you made the lines of the varying magnetic field return elsewhere. Now V1 and V2 are equal to V3 and V4, respectively. This means that the sum of the voltages around the inner loop is 1V, which rightfully violates Kirchhoff. So this is not an ideal transformer anymore. This is just a regular circuit subject to induction like simply all real circuits.
QuoteHave you ever did AC circuit analysis my hand? If you did then i would have assumed you would have less trouble understanding what an inductor is.
I do not have any trouble with inductors. I designed and built an isolation transformer and documented it on the Internet. Do you remember?
QuoteWhat exactly are you trying to prove with that diagram? We all know you can't just directly use Kirchhoffs circuit laws inside real world magnetic fields. Did anyone say you can?
The voltages are not measured inside the field. An inductor is the simplest circuit mesh possible. It's just a piece of wire connected to whatever. The voltage across the piece of wire is always zero. The voltage across whatever is different from zero. If you add them up you get something different from zero.
Read Feynman once more and if you still don't understand, maybe we can help.
QuoteWell yeah its a special case where circuit meshes (Where KVL is meant to be used) without realistically modeled wires happen to behave the same as a real world circuit.
No. Stop this pseudo-scientific talk. KVL is a special case of Faraday when there's no varying magnetic field inside the circuit. Repeat until enlightened.
QuoteBoth Maxwell and Kirchhoff work just fine when used correctly. So why is it a problem that there are two ways to go about calculating electrical circuit behavior?
There's ONLY ONE theory to explain electricity and magnetism: Maxwell, and Kirchhoff is just a special case of it. This is a tried and proven truth.
What part of Feynmans lecture did i understand wrong?
Ah alright that's what is bothering you, alright fine il do some drawing too.
I wonder when you realize that those guys do not have word "agree" in their vocabulary :D
Perfect. Now let's suppose that I define two paths: #1 from A to B and #2 from B to A. Let's suppose, then, that the voltages measured between these two points following these two different paths are different. If we start form point A via path #1 and return to it via path #2, and if we add up these two voltages, will we have zero volts?
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=631588;image)
Following the circuit analysis definition of voltage:
Path1: Amount of charge separation caused by the EMF in the wire
Loop1 EMF: 1V * 0.1334 = 133.4mV
Path2: Same two points so same voltage: 133.4 mV
If your results don't agree please also explain how you reached your numbers.
I do not want to spoil bsfeechannel's fun, so I will only pose a question.
Following the textbook definition of voltage
Path1: 0V (Because as you said there is a wire there that nulls out the sum of E fields)
Path2: No wire to null the field so the voltage is purely the EMF around that path, however the EMF was specified for the whole loop so Path1 has to be subtracted out
Total Area of loop: 35.295 cm2
Total EMF voltage around the loop: 1V
Loop area occupied by Path1: 4.71 cm2
Loop area ratio: 4.71 / 35.295 = 0.1334
Loop2 EMF: 1V * (1-0.1334) = 866.6 mV
Following the circuit analysis definition of voltage:
Path1: Amount of charge separation caused by the EMF in the wire
Loop1 EMF: 1V * 0.1334 = 133.4mV
Path2: Same two points so same voltage: 133.4 mV
If your results don't agree please also explain how you reached your numbers.
Following the circuit analysis definition of voltage:
Path1: Amount of charge separation caused by the EMF in the wire
Loop1 EMF: 1V * 0.1334 = 133.4mV
Path2: Same two points so same voltage: 133.4 mV
If your results don't agree please also explain how you reached your numbers.
I do not want to spoil bsfeechannel's fun, so I will only pose a question.
To be clear, the unique, single-valued, 'circuit-analysis-defined' voltage across the physically tangible piece of wire has a value that depends on the area (or ratio thereof) that such wire define with an arbitrary imaginary path?
I mean, if the imaginary 'path #2' had a vertical side comprise between 2 and B, you would have found a different value for the unique circuit-analysis voltage? And another one, if it went way out on the left of the paper?
I think I owe you an apology. My drawing was not sufficiently clear. The magnetic field B should be spread uniformly all over the page. But that's OK, because the next step would be to make the magnetic field spread uniformly over the area like in the picture below. I.e., it is zero outside the loop formed by paths #1 and #2, and it is also zero for the blank portion of the same loop. B's intensity will be adjusted so that, together with that area (that you may consider square if you want), the EMF is still 1V.
I also forgot to say that the wire does not produce charge separation. It just "magically" nullifies any attempt at producing an electric field inside it. However you can keep on calculating your "circuit analysis definition of voltage" as if it were, if you want.
As for the voltage according to your "text definition of voltage", path #1 is OK, even with my unclear drawing. Path #2 I think would be a different value, but since my drawing is screwed, it is OK that at least you considered it different from zero.
So now, we're gonna use this ideal piece of wire to cover path #2 and we will leave path #1 free. We still need to know the voltage between points A and B. Let's see if our calculations will lead to the same value, shall we?
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=632479;image)
The dependence on Path2 comes from the fact that bsfeechannel defined the strength of the field being as strong to generate 1V of EMF for the entire loop. So given this being a uniform field means that a larger surface area always means more of the field is enclosed in the loop, this means the field has to be weaker to still produce 1V. Hence why making the loop area around Path2 larger causes the voltage on Path1 appear smaller because the field is still in the same spot but its weaker.
And what about path #1?
This makes sense, but, if the field is uniform - and you made no assumptions on what has generated it (remember the boundary conditions set by the shape of the primary coil?) how do you decide how to split the area? You assume the point with the B is the "origin" of the B field, and this term sounds a bit strange to me.
Are you assuming a circular generating coil so that the induced E field is directed along concentric circles centered at that point?
Oh, before I forget, I finally managed to scan my drawings about your 'magnetically shielded' circuit. Let me see if I can show you that your lumped circuit with four lumped coils is a different system from the unlumpable Romer-Lewin circuit.
Let's say we have a hypermu material that captures all magnetic field lines and lets nothing out. We put primary and secondary coil inside it in this way:
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=632611)
Fig. the hypermu shield
Now, let's look it as a cross section showing the B field lines entering and exiting the page. Since the material is magical, no field lines escape and I can exaggerate the holes needed to put our probes in. Circuit A1 is closest to the physical system, while circuit A2 is the same, but with the arc exaggerated.
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=632617)
Fig circuits A1 and A2
Do you recognize circuit (a) of my previous post? Here KVL works on both inner and outer circuit paths.
(Edit: with 'external circuit path' I mean the external voltmeter you placed to show 0V, as long as you enclose zero net (varying) magnetic field it behaves according to KVL)
(Edit: it seems I've used letters consistent with my previous post, after all)
Now, do you realize that systems A1 and A2 are different from system B, the Romer-Lewin ring?
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=632623)
Fig circuit A
Here KVL DIES on both inner and outer circuit paths. (the field lines close at infinity).
EDIT: added the missing "zero" before net magnetic field. Time to go to bed.
And what about path #1?[snip]
So in the more recent example yeah Path1 is 1V now.
I've corrected my captions, apologies for that. I believe you mean circuit (B) isQuote from: SredniNow, do you realize that systems A1 and A2 are different from system B, the Romer-Lewin ring?Well the way i see it is that Fig3 is sort of a zoomed in Fig2.
That depends how low do you define as being fundamental, so i'm going to go lower and lower in steps to hopefuly cover the level you are after.
Faraday law:
EMF Voltages comes from a loop area enclosing a changing magnetic field
Maxwell:
EMF Voltage comes from an the electric fields relation to the vector curl of the magnetic field.
Special relativity:
EMF Voltage comes from an apparent electric field generated by warping of spacetime due to the relative motion of charged particles.
Quantum electrodynamics:
EMF Voltage is the result of a moving observers interaction with a electromagnetic field trough the exchange of particles. (Please don't ask too many questions about this one because i don't really understand much about it)
Lewin is making assumptions from an incomplete / incorrect model by ignoring the current source while drawing his model for the Kirchof "law".
There really is no need to go any deeper into this.
We take a coil of Ideal Wire, put it between the poles of a magnet, with a commutator, and spin it around. What voltage is observed?
No EMF generated? Nothing?
Frustrated, you check the Ideal Wire datasheet again.
Inductance: 0 nH/m.
Hmmm.
Ideal Wire can't couple to a magnetic (or electric) field.
What about somewhere between Faraday and Maxwell?
For these two the ultimate cause of the EMF is the varying magnetic field. But OK, this means we can proceed.
Now let me introduce you to the resistor. Differently from our ideal wire, resistors do allow the existence of an electric field inside them. When connected to a circuit, they will let a current flow that is proportional to the line integral of the electric field along their paths divided by their resistance.
Now let's connect this resistor to our wire . A current will obviously flow from A to B. This will generate a magnetic field with a direction that will tend to oppose the magnetic field that generated the E.M.F. However, let's suppose that the resistance is sufficiently high, the current is too low, and consequently this opposing magnetic field is so weak that we can consider it negligible.
Let's suppose that R = 1k ohms (producing a 1mA current).
Using my drawing below, i.e. respecting the geometry of the paths, how would you please model this circuit using your circuit analysis technique?
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=633748;image)
Right. The whole point is that when the lines close at infinity or, for what matters outside your lab, you have no way to access the circuit without having a net varying B field enclosed by the circuit's path. And this is what makes KVL fail.
Look better: in one case you cannot get rid of the varying B field inside the circuit path. The reason is that the 'returning lines' are way out of your reach. So you cannot 'hide' the whole field inside the components, hence you cannot have lumped components.
If you cannot see this, I don't know how to help you.
As for the rest, man, are you sure you do not have a reset button somewhere? I really mean no disrespect (I believe we've been able to argue without resorting to insults and keeping it quite polite) but... the way you try to compute 'partial emfs' based on areas makes me think of cargo cult science.
Using the area ratios works as long as the symmetry of the system allows it such as in the case of primary and secondary circular coils on the same axis. When they are off center, or have a different shapes, things are not so easy. So, while it is true that you get different results according to where the circuit is placed inside the field (let's focus on the field generated by a circular primary coil), you need to take the shape of the induced E field into account if you want to find the path integral on a portion of the closed curve (or the distribution of surface charge on the conductor).
(EDIT: come to think of it again, it seems that all is required is that the primary coil be circular as that seems the only way to get a uniformly distributed magnetic field inside. Someone has proof of that?)
And regarding the 'origin of the field' as the point where field lines stay put when you change the intensity... It looks intriguing, but does it have any physical motivation? To me is just a graphical representation, nothing more. You seem to think that when the field diminishes in strength the 'number of points' where you can find the B field diminished as well...
Edit: corrected duplicate "positioning" with "shapes"
Edit: grammar
EDIT: different --> equivalent. Man, I really need to sleep better. That fucking neighbor's dog, I can hear him with all windows closed. Maybe a 400W ultrasound whistle...
I suppose if you want a physical representation of field lines in 3D you could imagine each field line being a long stringy bar magnet. All of those long bar magnets have the same magnetic flux and they contain all of this flux inside of them. So if you ware to recreate the field in a loop of wire using these stringy bar magnets as the current is ramping up you would find more and more of these magnets appearing at the edge of the loop and moving towards the center. If we now look at the 2D cross section of the area inside the loop it would look like a area of uniformly distributed dots that is "compressing together" around the center point, putting more and more of them into view as they get closer together. This is sort of analogues to a magnetic field moving inwards so a conductor going around this center point feels the same effect as if it was moving trough a magnetic field. This lets you think about it analogous to the explanation of a comutated DC motor/generator, we also have an equation for calculating the size of this voltage its Uemf=v*B*l .Similarly the force generated by a current carrying wire in a magnetic field can be calculated, putting both together gives you a connection between mechanical power and electrical power in the wire. None of this requires a defined loop area, just a section of wire. Look it up yourself instead of just reading my words.
(EDIT: come to think of it again, it seems that all is required is that the primary coil be circular as that seems the only way to get a uniformly distributed magnetic field inside. Someone has proof of that?)
(EDIT: come to think of it again, it seems that all is required is that the primary coil be circular as that seems the only way to get a uniformly distributed magnetic field inside. Someone has proof of that?)
If the solenoid is infinite or very long such that the field lines are parallel and the field outside can be neglected, then the field inside will be uniform. This can be proven by Ampere's law. Choose a rectangular path parallel and perpendicular to the field and surrounding some turns of the solenoid. Vary the position of the side of the path that is inside the solenoid. Then since the current surrounded by the path is always the same, the internal field must also always be the same, no matter what position.
The solenoid doesn't have to be circular. It should work for any shape as long as the other conditions are met.
This is where thinking about "field lines" causes a problem. In this case of a changing magnetic flux, nothing is moving. The geometry of the magnetic field does not move. By that I mean that at every point, the direction of the magnetic field vector doesn't change. Only the amplitude changes.
The magnetic field is not creating a force to move the charges in the wire. That force would be perpendicular to the wire, so it would have no effect on the current.
Faraday's law says that a magnetic field that is changing with time creates an electric field that rotates around the magnetic flux. It is the electric field, not the magnetic field that moves the charge and creates the current.
This has nothing to do with special relativity. It is just Faraday's law.
The Cyan arrows are the E field forced forced upon the world. This is essentially the path of a wire connected to a power source.
@Berni
Can you create a trapezoidal (the more asymmetric the better) primary coil and then compute the line integrals on the sides of a square coil placed off-center (where 'center' is where the E field appears to go around), like the square I posted?
Alternatively, instead of color-coding amplitudes, draw arrows with lenght proportional to the amplitude (but this might lead to too long and too short arrows...).
The circuit is simple enough that very little circuit analysis is actually needed on it.
We know the voltage around it is 1V, We know the total loop resistance is 1 KOhm so trough I=U/R=1V / 1KOhm = 1mA.
At this point the voltages and currents across components are known so the circuit is solved.
Since you are looking for the textbook definition the voltage between points AB is both 0V and 1V.
Well, clearly Kirchhoff doesn't hold for the most elementary of the circuits when varying magnetic fields are present.
What you might have tried to do (at least I have) was to replace the wire and the field by a battery or some other lumped generator like in the picture below.
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=636847;image)
However, when you do that, obviously you will have to account for the electric field that this component will introduce along path #2. But path#2, we've already seen, has no electric field. So this is not a circuit of exclusively lumped components and no circuit analysis from the point of view of Kirchhoff can be employed.
But all is not lost. The answer to the next question may seem kind of obvious, but I am trying to prevent any hasty conclusions. I had to spend some time meditating about it myself.
I elongated path #2 so that we have a larger area without any varying magnetic field to the right like in the picture below. My question is, please, what is the voltage between points A' and B' via path #3?
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=636853;image)
The voltage along that path is also 1V because i assume there is no wire there.
Node | Node | Path | Voltage (V) | Reason |
A' | A | #2 | 0 | Ideal wire |
A | B | #1 | 1 | EMF across resistor |
B | B' | #2 | 0 | Ideal wire |
B' | A' | #3 | -1 | EMF across the air |
A' | B' | #3 | 1 | EMF across the air |
B' | A' | #2 | 0 | Ideal wire |
Node | Node | Path | Voltage (V) | Reason |
A' | A | #2 | 0 | Ideal wire |
A | B | #1 | 1 | EMF across resistor |
B | B' | #2 | 0 | Ideal wire |
B' | A' | #3 | -1 | EMF across the air || battery |
Total | 0 | No varying magnetic field in the mesh | ||
A' | B' | #3 | 1 | EMF across the air || battery |
B' | A' | #2 | 0 | Ideal wire |
Total | 1 | Presence of varying magnetic field in the mesh |
Node | Node | Path | Voltage (V) | Reason |
A' | A | #2 | 0 | Ideal wire |
A | B | #1 | 1 | EMF across resistor |
B | B' | #2 | 0 | Ideal wire |
B' | A' | #3 | -1 | Battery |
Total | 0 | No varying magnetic field in the mesh |
Node | Node | Path | Voltage (V) | Reason |
A'' | B'' | #4 | 1 | EMF across the air |
B'' | A'' | #2 | 0 | Ideal wire |
Total | 1 | Presence of varying magnetic field in the closed path |
I am grateful to Mr. Sadaghdar for a number of discussions about Faraday’s Law and KVL, which have improved my understanding of both.I.e., my understanding improved.
Many introductory texts on electromagnetism are not precise about what exactly they mean by the voltage drop across the inductor, and many students come to incorrect conclusions about what this actually means. The most common misconception is that the - LdI/dt voltage read by the voltmeter just above represents a −∫abE⋅dl through the inductor. But if the inductor wires are perfectly conducting, this integral is zero because there is no electric field in the wires.
Thank you for all your replies.
We can see pretty much that this is theoretically and physically impossible, because a battery and a resistor can't occupy the same space at the same time.
So, not only this circuit more than violates--it rapes--Kirchhoff big time, as we have seen, but also cannot have an equivalent version with lumped components.
Now I owe you an answer to your question, what part of Feynman's lectures, namely Chapter 22 is being misunderstood? The short answer is all of it. It is so because people are disregarding basic assumptions that Feynman adamantly stresses in his text.
An answer a little less short is given by Prof. Belcher in his "MIT-quality report" where he elegantly showed where exactly Mehdi, and for that matter all those who still believe that KVL can have the slightest chance to hold under a varying magnetic field, goofed it up. However, after the report, Mehdi continued to espouse his previous ideas, which means that he didn't in fact learn anything. Perhaps, noticing this, even before Mehdi made his second video, Prof. Belcher said in his report:QuoteI am grateful to Mr. Sadaghdar for a number of discussions about Faraday’s Law and KVL, which have improved my understanding of both.I.e., my understanding improved.
Belcher concludes:QuoteMany introductory texts on electromagnetism are not precise about what exactly they mean by the voltage drop across the inductor, and many students come to incorrect conclusions about what this actually means. The most common misconception is that the - LdI/dt voltage read by the voltmeter just above represents a −∫abE⋅dl through the inductor. But if the inductor wires are perfectly conducting, this integral is zero because there is no electric field in the wires.
So, replacing perfectly conducting wires with batteries, or generators, is a noob mistake. It's a trap for young players. This means that the circuit below is not modelling Lewin's circuit.
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=638728;image)
In fact, Lewin's circuit is not lumpable, because we do not have anywhere inside the loop where we don't have varying magnetic fields, where we could replace the EMF with a battery and get away with it. The voltages that you can measure at the terminals of the resistors of the internal loop are the result of electric fields that are being generated along the very same path where the resistors are.
The failure to understand this basic principle of electromagnetism leads to all kinds of wrong conclusions.
- All other elements are not enclosed in a magnetic field so circuit analysis methods should work on them.
Well in terms of being unlumpable i still don't see how my lumped transformer model is wrong here:
https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/msg2138140/#msg2138140 (https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/msg2138140/#msg2138140)
[snip]
No need to tell me that a mesh model is not exactly the same as a real circuit. I know its not! No mesh model is, because we can't create these ideal circuit components in real life, but when modeling is done right it acts just like the real thing despite being simplified.
I said in my last post that i know its not the exact same circuit.
But where do you draw the line.
But where do you draw the line.
Your model says you will find 250mV across all wires. Theory says it is zero.
Your model says you will find 250mV across all wires. Theory says it is zero.
Which exactly theory says it is zero?
Are you saying that for EMF voltage to appear - full winding is necessary? In your understanding there is no 1/4 * EMF voltage on the 1/4 winding (tap)?
Are you saying that for EMF voltage to appear - full winding is necessary? In your understanding there is no 1/4 * EMF voltage on the 1/4 winding (tap)?
Where have you been lately? Have you followed our discussion since Jan 23rd?
I can't do better.
What 1V jump is there? Its simply voltages measured across the wires inside the magnetic field by taking a different path with the voltmeter. The voltages are there in Dr. Lewins experimental circuit if you probe it just the right way.
The lumped model simply has a different way of expressing the effects of magnetic fields, that's it.
The whole circuit still acts identical and that's what matters. Cirucit mesh models are supposed to model the high level behavior of circuits, not model physical electrons moving trough wires and the fields they make around them.
As long as the circuit behaves the same its considered a accurate model.
I don't know how to answer your question without further investigation. Let's suppose that we have a varying magnetic field so that going from point A and returning to it again via the path indicated by the dashed line, we find an EMF = 1V like in the picture below.
Now consider that we introduce a piece of wire along the same path so that we have 3/4 of a turn, 1/2 a turn and 1/4 of a turn. What would be the voltages VAB
Unfortunately your "model" doesn't behave the same as Lewin's circuit nor is accurate. In fact it is aberrant. And, if you pardon me, asinine. It proposes the existence of 250mV across a wire that has a resistance of about zero ohms carrying a current of 1mA.
250mV = 0Ω · 1mA !!!!!!!!!!!!!
I was talking about 1/4 (part) of the winding/turn. No need to introduce anything. It was simple question. - Transformer with single winding/turn with 1/4-turn tap. What's voltage on it if full winding gives 1V?
Unfortunately your "model" doesn't behave the same as Lewin's circuit nor is accurate. In fact it is aberrant. And, if you pardon me, asinine. It proposes the existence of 250mV across a wire that has a resistance of about zero ohms carrying a current of 1mA.
250mV = 0Ω · 1mA !!!!!!!!!!!!!
You say you mastered Maxwell's equations? :-DD :-DD :-DD :-DD :-DD :-DD
I was talking about 1/4 (part) of the winding/turn. No need to introduce anything. It was simple question. - Transformer with single winding/turn with 1/4-turn tap. What's voltage on it if full winding gives 1V?
Can you, please provide a schematic of how you get a 1/4 tap from a transformer with a single-turn winding?
Unfortunately your "model" doesn't behave the same as Lewin's circuit nor is accurate. In fact it is aberrant. And, if you pardon me, asinine. It proposes the existence of 250mV across a wire that has a resistance of about zero ohms carrying a current of 1mA.
250mV = 0Ω · 1mA !!!!!!!!!!!!!
You say you mastered Maxwell's equations? :-DD :-DD :-DD :-DD :-DD :-DD
Isn't that hilarious? A static wire with a next to zero ohm internal resistance sporting 250mVDC and 1mA!!!
It doesn't need to be a Maxwell expert to realize how moronic that conclusion is. I agree with you.
This one is good enough. There are loads of 1/4 windings, with voltmeters attached:
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=630190;image)
Right. So you agree that you do not know what EMF actually is.
What is the EMF?
Where is the transformer?
https://en.wikipedia.org/wiki/Electromotive_force (https://en.wikipedia.org/wiki/Electromotive_force)
Dr.Lewin's experiment is transformer. Didn't you notice? :palm:
Isn't that hilarious? A static wire with a next to zero ohm internal resistance sporting 250mVDC and 1mA!!!
It doesn't need to be a Maxwell expert to realize how moronic that conclusion is. I agree with you.
QuoteDr.Lewin's experiment is transformer. Didn't you notice? :palm:
So any circuit under a varying magnetic field is a transformer?
Transformer with single winding/turn with 1/4-turn tap. What's voltage on it if full winding gives 1V?
Isn't that hilarious? A static wire with a next to zero ohm internal resistance sporting 250mVDC and 1mA!!!
It doesn't need to be a Maxwell expert to realize how moronic that conclusion is. I agree with you.
Take any Li-Ion battery and put it into your reasoning ;)
I did not say any circuit. I said that Dr.Lewin's experiment is transformer.
You are clearly avoiding my quite straight and simple question:Transformer with single winding/turn with 1/4-turn tap. What's voltage on it if full winding gives 1V?
Isn't that hilarious? A static wire with a next to zero ohm internal resistance sporting 250mVDC and 1mA!!!
It doesn't need to be a Maxwell expert to realize how moronic that conclusion is. I agree with you.
Take any Li-Ion battery and put it into your reasoning ;)
Got it. I'll replace the batteries of my cell phone by a piece of wire. Why didn't i think of that before?
But since you said it is a transformer, what are the criteria to consider a circuit under a varying magnetic field a transformer?
Maybe you're asking the wrong questions.
Batteries have electric fields inside them.
Isn't that hilarious? A static wire with a next to zero ohm internal resistance sporting 250mVDC and 1mA!!!
Since you do not know what is transformer - why do you even participate in this discussion?
You just pretend that you do not understand what I am asking.
So what? How does it changes Ohm's law you mentioned?Wires are not batteries.
Im talking about the field around it due to us all agreeing that circuit analysis (And with that also KVL) works when there is no field.
:-DD :-DD :-DD :-DD :-DD :-DD
:-DD :-DD :-DD :-DD :-DD :-DD
It's Groundhog Day.
Again!
OK, probably way off topic, but I guess I'm losing my mind. I watched this video. What the hell? Could something on the internet not be right? Or am I confused? How could this guy get the fields so wrong? He doesn't even agree with Wikipedia. So I can't believe everything on the internet? :
(https://upload.wikimedia.org/wikipedia/commons/thumb/8/82/Poynting_vectors_of_DC_circuit.svg/660px-Poynting_vectors_of_DC_circuit.svg.png)
Yikes. "We have a strong electric field inside the wire":
Comments are overwelmingly positive "mind blown"!
OK, probably way off topic, but I guess I'm losing my mind. I watched this video. What the hell? Could something on the internet not be right? Or am I confused? How could this guy get the fields so wrong? He doesn't even agree with Wikipedia. So I can't believe everything on the internet? :
(https://upload.wikimedia.org/wikipedia/commons/thumb/8/82/Poynting_vectors_of_DC_circuit.svg/660px-Poynting_vectors_of_DC_circuit.svg.png)
Yikes. "We have a strong electric field inside the wire":
https://youtu.be/C7tQJ42nGno (https://youtu.be/C7tQJ42nGno)
Comments are overwelmingly positive "mind blown"!
I got a rather interesting comment once, in fact I've had more than once in various forms, but the comment was basically: how do we know you're RIGHT? How can we take your word for it? On, you know, all these things and all these topics? And, well, you know, it's a really good question, and the answer is you SHOULDN'T. You should never take anyone's word for it. Don't take anything i say on these blogs as gospel. Uh, you know, I've been in the industry for 20 years so, you know, I like to think I do know what I'm talking about mostly. But, you know, don't take my word for it. All my blogs, and all the things I talk about on here are designed to be food for thought. You're supposed to use your own engineering judgment and, you know, and go out and verify things. If you're, you know, if you're really interested in something, don't complain that i didn't explain it right or and you know i might have got it a bit wrong or something like that. Go out and investigate for yourself. That's what it's all about: food for thought.
OK, probably way off topic, but I guess I'm losing my mind. I watched this video. What the hell? Could something on the internet not be right? Or am I confused? How could this guy get the fields so wrong? He doesn't even agree with Wikipedia. So I can't believe everything on the internet? :
Yikes. "We have a strong electric field inside the wire"
Comments are overwelmingly positive "mind blown"!
So, you keep asking what is the voltage across a quarter turn, but you have to tell us where is the varying magnetic field region and along which path among the infinitely many you want to compute that voltage. You might end up with a quarter of a volt but also with much less.
So, you keep asking what is the voltage across a quarter turn, but you have to tell us where is the varying magnetic field region and along which path among the infinitely many you want to compute that voltage. You might end up with a quarter of a volt but also with much less.
I said "transformer" which means magnetic fields are contained, they do not influence voltmeter leads. I say 1/4 turn will give 1/4 V EMF. Do you agree?
So, you keep asking what is the voltage across a quarter turn, but you have to tell us where is the varying magnetic field region and along which path among the infinitely many you want to compute that voltage. You might end up with a quarter of a volt but also with much less.
I said "transformer" which means magnetic fields are contained, they do not influence voltmeter leads. I say 1/4 turn will give 1/4 V EMF. Do you agree?
As I said before, you have to specify where the B field region is and where your path is. Post a picture of your quarter of a transformer with a shaded region showing where the B field varies and we'll see if we agree or not. You might discover that while you can have the field contained with a quarter of an arc, you no longer can have it when you consider that arc as part of a circular 'transformer'. Unless you consider a different system, like the one I showed Berni a few pages back.
But please, post the picture, so that we can be sure what we are talking about.
Edit: plurals, it appears I place those at random.
So you don't know what magnetically shielded transformer is, I have to show picture?
So you don't know what magnetically shielded transformer is, I have to show picture? :-// Do you know what voltmeter is? Or wire?
Shall I show picture of voltmeter and wire as well?
Just draw your quarter circle isolated transformer, please.
Or, as Rihanna would put it: "Shut up and draw!"
I can see the picture in your previous post and that is not what I asked you to draw. I asked you to draw your "1/4 turn magnetically isolated transformer" highlighting the region of space where the dB/dt happens, so that we can reason on that.
Can't you do it? There is more than a way to do it and you are undecided? Pick one. We'll go from that.
Maybe you did not read the last 32 pages but the whole point of this thread is that there are people like you who believe the Romer-Lewin ring is lumpable, and people like me who believe it isn't.
I said "transformer" which means magnetic fields are contained, they do not influence voltmeter leads. I say 1/4 turn will give 1/4 V EMF. Do you agree?
where do the magnetic field lines return?, the way it is drawn they return at infinity
EDIT: added boldface to highlight the part that should make it clear that the field is NOT contained.
[edit] I repeat question - what will be voltage shown by voltmeter V2?
You say the voltage that the voltmeter will show is 250mV, but Mabilde and Mehdi, two other kirchhoffools like you, measured 0V (Mehdi's fist video @6:42 and Mabilde @21:55). Of course, they came with stupid explanations as to why the voltage they measured didn't match their expectations, while Faraday's law was predicting exactly what they measured.
Kirchhoffools' claims are so flawed that they can't even agree with each other. Pathetic.
Most ridiculous debate imaginable. I said that magnetic field is contained, your argument is "should make it clear that the field is NOT contained".
[edit] BTW You did not answer the question about indication of "voltmeter V2"
Don't be mad that I am using your mistake as an argument :DI'm not mad, why would I be?
Mehi's video @6:42 do not measure 0V
[edit] In case you did not notice, we don't talk about Kirchoff's rules at all, yet you manage to mention them, insulting way. THAT's pathetic
The fact that you say the field is contained does not mean that it is contained.
You have to contain all the lines of the magnetic field. Like in a toroidal transformer, or an M or EI transformer.
QuoteMehi's video @6:42 do not measure 0V
Oh yes he does. I'm referring to the original video, the one Dave posted.
No, you don't understand. It's not that there is a little leakage: the whole lot of field lines are missing! In the infinitely long solenoid you miss the 'return' lines. So it's impossible to contain the field.
You can force the field lines into a high magnetic permeability material, and I also produced a drawing, but that systems is a DIFFERENT systems from the infinitely long solenoid.
I hope it is clear now.
I produced a drawing.
Do the same: draw your quarter turn magnetically isolated transformer and I will answer your question.
I do not need to. Picture I did show is good enough. Inside two circuit loops there's magnetic field and it is specifically shown where's no magnetic filed, indicated by note "no magnetic field here" (leads of voltmeter "V2") - meaning leads of voltmeter "V2" are not influenced by magnetic field. Do you have problem to understand that circuit or what?
[edit] I repeat question - what will be voltage shown by voltmeter V2?
QuoteMehi's video @6:42 do not measure 0V
Oh yes he does. I'm referring to the original video, the one Dave posted.
Well, you are welcome to show where Mehdi measure 0V. With timestamped screenshot & YT link.
Well does anyone also notice that the solenoid used in Dr. Lewins experiment is significantly shorter than infinity. It is smaller than the height of a HP digitizing scope.
So then is his experiment a scam because he is not recreating the same circuit as on the blackboard or does it simply just not matter?
Well does anyone also notice that the solenoid used in Dr. Lewins experiment is significantly shorter than infinity. It is smaller than the height of a HP digitizing scope.
So then is his experiment a scam because he is not recreating the same circuit as on the blackboard or does it simply just not matter?
Never said he claimed anything about lumping, you are welcome to find me a quote for that.
Exactly as you say, his magnetic flux around the circuit is not the same as what he drew on the blackboard. And this was exactly your argument against using a lumped transformer. So in what way is the situation different for Dr. Lewins experimental setup? His experiment also doesn't doesn't exactly match the circuit drawing, yet acts exactly like the math says that drawing should act.
calm down children please.....
You can get rid of that unwanted flux because you are trying to model the ideal case of an infinitely long solenoid where that leakage flux is exactly zero. Or, if you prefer, you can get rid of the effects of that unwanted flux because it has no effect on the two resistor loop.
Then explain why the results still match the experiment if its the wrong way to do it?
Then explain why the results still match the experiment if its the wrong way to do it?
They don't. Only the voltages across the resistors are the same. The voltages in the wires are not. In Lewin's circuit the voltages are zero. Yours have 250mV. Huge difference.
If you do that in real life (by choosing a path with 0V EMF because we don't have these mythical ideal wires) you get the voltmeter also showing 250mV.
Well does anyone also notice that the solenoid used in Dr. Lewins experiment is significantly shorter than infinity. It is smaller than the height of a HP digitizing scope.
So then is his experiment a scam because he is not recreating the same circuit as on the blackboard or does it simply just not matter?
Well does anyone also notice that the solenoid used in Dr. Lewins experiment is significantly shorter than infinity. It is smaller than the height of a HP digitizing scope.
So then is his experiment a scam because he is not recreating the same circuit as on the blackboard or does it simply just not matter?
It doesn't matter to him. He's trying to make a fundamental physics point and found a way, any way, regardless if it's a good or accurate practical analogy or not, to do it. He's never really addressed this, and probably think he doesn't have to because his theory is not wrong.
Well does anyone also notice that the solenoid used in Dr. Lewins experiment is significantly shorter than infinity. It is smaller than the height of a HP digitizing scope.
So then is his experiment a scam because he is not recreating the same circuit as on the blackboard or does it simply just not matter?
It doesn't matter to him. He's trying to make a fundamental physics point and found a way, any way, regardless if it's a good or accurate practical analogy or not, to do it. He's never really addressed this, and probably think he doesn't have to because his theory is not wrong.
I think you nailed it. Getting stuck to his (in)famous experiment and trying to criticize, explain, praise or debunk it, as many of us have done one way or another, turns out completely pointless.
You're right, it's about fundamental physics, and whereas I still think the experiment itself is flawed, and has led some of us to misinterpret his point at first, he probably couldn't care less.
I still think he's caused enough confusion to many - you just need to look at this endless thread - that his approach is pedagogically flawed. As I noted much earlier, his written courses are actually much clearer than the drama he tends to make with his oral lectures - at least IMO. But I know you have to keep your students attentive. Or at least "entertained"...
The good point is that this has raised a series of interesting questioning. And after all, if this was his intention, that's well done.
Well does anyone also notice that the solenoid used in Dr. Lewins experiment is significantly shorter than infinity. It is smaller than the height of a HP digitizing scope.
So then is his experiment a scam because he is not recreating the same circuit as on the blackboard or does it simply just not matter?
It doesn't matter to him. He's trying to make a fundamental physics point and found a way, any way, regardless if it's a good or accurate practical analogy or not, to do it. He's never really addressed this, and probably think he doesn't have to because his theory is not wrong.
He touched on highly sensitive taboo, or myth, that is the validity of Kirchhoff's laws. Those who bash him are exactly those who consider RF, or anything Maxwell related, black magic.
The phenomenon is exactly the same.
The only spot i disagree with Dr. Lewin is the use of KVL on a circuit that has not been modeled to include the magnetic properties of wires.
So what is always true is that the sum of the electric field E and the cross product of the velocity of the conductor and the magnetic field B—which is the total force on a unit charge—must have the value zero inside the conductor:
F/unit charge = E+v×B = 0 (in a perfect conductor), (22.12)
where v represents the velocity of the conductor. Our earlier statement that there is no electric field inside a perfect conductor is all right if the velocity v of the conductor is zero;
Once they are modeled everything works fine and gives identical results without any sort of paradox.
The phenomenon is exactly the same.
You say that circuit of Dr.Lewin's experiment at RF frequencies like 3GHz acts same way as 300Hz?
You say that circuit of Dr.Lewin's experiment at RF frequencies like 3GHz acts same way as 300Hz?
Let me see. To explain Lewin's circuit, we need Maxwell's equations. To explain how a loop antenna works, we need Maxwell's equations. I'm starting to see a coincidence there.
Your BS answer actually proves my point :D
Yes we can argue about what a wire is, ask a chemist and he will see a large number of copper atoms arranged in to a rod shape with some on the outside being bound to oxygen. From the point of view of circuit analysis the wire is a magnetic component because the current inside it interacts with the magnetic field, much like a capacitor is an electrostatic component (Even if its just parasitic capacitance between two wires rather than an actual component with parallel plates inside)The only spot i disagree with Dr. Lewin is the use of KVL on a circuit that has not been modeled to include the magnetic properties of wires.The wires do not have "magnetic properties". The only way for a wire to "react" to magnetic field is if it is moving in relation to a frame of reference.
This is stated clearly in Feynman's chapter 22:
From the point of view of circuit analysis the wire is a magnetic component because the current inside it interacts with the magnetic field, much like a capacitor is an electrostatic component (Even if its just parasitic capacitance between two wires rather than an actual component with parallel plates inside)
To prove my point that you can measure 0V or 250mV depending on what you want to see i have put together some examples:
So there you go, that's how you measure 250mV in there, if you don't believe me go on and try building one of these circuits to see for yourself.
Circuit analysis stays perfectly consistent when you model things correctly.
If its 0V that you want to see just look at circuits in figures 2a 2b 2c and see it is indeed 0V. Happy now?
There is no paradox with this circuit as long as its correctly modeled.
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=646799;image)
So everything is in one plane, 2 dimensional.
Now what do you measure? Does it matter if the scope is on the left side or the right side?
What if you measure a quarter turn of the wire? Do you get 0V, or something else?
I don't want to see 0V. Nature shows it is 0V.
Mehdi and Mabilde reconstructed Lewin's circuit. Mabilde got even to the point of recreating Lewin's solenoid.
They thought like you: there must be a voltage in the wires. Lewin goofed it up. He bad probed the whole thing. He doesn't know how to lump model his circuit.
When they measured exactly zero volts they got puzzled, and invented each their own completely different convoluted pseudo-scientific theory to explain what the Maxwell's equations predict with simplicity and elegance: there are no voltages in the wires, nor in the probes, Kirchhoff doesn't hold for varying magnetic fields in a circuit, Faraday's law is what accounts for the voltages across the resistors, nothing else.
QuoteThere is no paradox with this circuit as long as its correctly modeled.
The only thing your circuit is modeling is the lack of understanding of electromagnetism.
Your version contradicts Mehdi's version which contradicts Mabilde's version. Which shows that the assumption that Kirchhoff always holds for varying magnetic fields is self-contradictory, i.e. is a paradox. Which is what Lewin brilliantly showed.
Since it is impossible to lump model Lewin's circuit nor any other circuit with varying magnetic fields in them, the paradox ceases to exist when you realize that the only way to solve them is to apply Faraday's law and give Kirchhoff and his doggone "law" to what it deserves: the birds.
If you know enough about circuit meshes you also know that you can't have any voltage jumps within the same net, hence why a component is introduced into the mesh to represent the voltage jump, this component is what represents the potential across the ends of the wire. There is Faradays law itself inside that component.
All i did was show that Dr. Lewins circuit can be lump modeled just fine and that the resulting circuit mesh behaves identically while causing no paradoxes.
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=646799;image)
So everything is in one plane, 2 dimensional.
Now what do you measure? Does it matter if the scope is on the left side or the right side?
What if you measure a quarter turn of the wire? Do you get 0V, or something else?
Typical coax cable doesn't really give any shielding to magnetic fields so the scope would show different values depending on what side it is on. If the shielding material on the coax cable is made of a infinite permeability material then you should get the same value no matter where you put the scope. Same difference as Figures 1 and 2 in my post, its a different magnetic path.
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=646799;image)
So everything is in one plane, 2 dimensional.
Now what do you measure? Does it matter if the scope is on the left side or the right side?
What if you measure a quarter turn of the wire? Do you get 0V, or something else?
Typical coax cable doesn't really give any shielding to magnetic fields so the scope would show different values depending on what side it is on. If the shielding material on the coax cable is made of a infinite permeability material then you should get the same value no matter where you put the scope. Same difference as Figures 1 and 2 in my post, its a different magnetic path.
There are no magnetic fields where the coax is. You yourself simulated the field pattern for a solenoid. There is only an electric field. The coax should have some effect with an electric field present.
Yes the conductive shield around a coax does make it immune to electrostatic fields as the charges in the shield will redistribute to perfectly oppose it. However the non conservative field caused by the vicinity of a magnetic field is not the same thing.This is a quasi-electrostatic situation, at least the way Romer set up the experiment. The electric field is constant during the measurement period.
The reason Romer uses coax cable...I don't see any mention of coax cable in Romer's paper.
Yes so you take the dotted Γ line in a path that encloses no net field, everything else is solved using Maxwell and everything is fine.
If this is the wrong way to apply circuit analysis can you then explain why all the voltmeters still show correct values regardless if the type of analysis applied is Faradays loop equation or just circuit analysis as a transformer? If the voltmeters are supposed to show something else feel free to point it out.
(Regarding to this post: https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/msg2182160/#msg2182160 (https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/msg2182160/#msg2182160) )
If its wrong you should be able to make it spit out wrong results too (at least using some special case circuit if not in general).
It is wrong because you added "compensation" to your probes to account for a non existing voltage in the wires.
You know, this is the problem with using Spice as a learning tool. Spice is a stupid software with no critical thinking. If your premises are wrong it will accept them as truth and will sheepishly confirm whatever wrong conclusions you have drawn.
Ditch this devilish program at once and learn electromagnetism as it should: studying the classics, like Feynman's lectures and such.
Where is the compensation? I'm just treating the probe wires the same way as the circuit wires since they follow the same path. Should wires that connect voltmeters be treated in some special way?
And what is wrong with SPICE?
The difference between a purely electrostatic field and one induced by a magnetic field is the non conservative part. This gives the field ability to push electrons around closed loops of conductor while a electrostatic field can only redistribute them but not sustain a current apart from the very brief transient as they redistribute.
Since the inner conductor forms a continuous loop trough the voltmeter, it means that the the field can push the electrons around it and create a current that the voltmeter detects as voltage across its internal resistance. The shield however does not form a continuous loop and as such can't experience any current trough it.
...My point is that the coax shield in this configuration has no effect.
I don't see why you would need current to shield a static electric field.Quote...My point is that the coax shield in this configuration has no effect.
I'm not convinced. I expect the coax will shield the center conductor from the induced electric field. So you would measure the same voltage whether the scope was on the left or the right side.
Does bsfeechannel’s thesis hold?
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=648777;image)
calm down children please.....
The topic was getting heated and was reported, I in turn was trying to jest in calming things down without upsetting anyone.
I am probably old enough to be your father, so don't you fucking call people you don't know children
I am probably old enough to be your father, so don't you fucking call people you don't know children
Seems, you have issues. Don't act like kid if you don't like to be labelled as such. By deleting your posts you did not act like a man at all. Attitude you show now is disgusting.
Umm, you know, when things get heated, a certain number of people always abuse the "report to moderator" button. It's their way of dealing with the emotions.
As for the mod who banned me (which I presume it's you given the timing), let me teach you a lesson in what a moderator should do. A moderator should protect the discussion, not their fragile ego. Can you point out what granted me a seven day ban, except for the fact that I responded to a silly remark in jest?
P.S.
I removed only the technical parts from my previous posts. I left all that remained.
I think you nailed it. Getting stuck to his (in)famous experiment and trying to criticize, explain, praise or debunk it, as many of us have done one way or another, turns out completely pointless.At first, that's what I thought. Lewin was right but messed things up when trying to explain it. However after, what?, three or four months discussing about the subject, reading and re-reading papers, books, analyzing the videos, etc., and even performing experiments in my lab, I came to conclusion that the one who nailed it was exactly Lewin.
You're right, it's about fundamental physics, and whereas I still think the experiment itself is flawed, and has led some of us to misinterpret his point at first, he probably couldn't care less.
I still think he's caused enough confusion to many - you just need to look at this endless thread - that his approach is pedagogically flawed. As I noted much earlier, his written courses are actually much clearer than the drama he tends to make with his oral lectures - at least IMO. But I know you have to keep your students attentive. Or at least "entertained"...
The good point is that this has raised a series of interesting questioning. And after all, if this was his intention, that's well done.
He touched on highly sensitive taboo, or myth, that is the validity of Kirchhoff's laws. Those who bash him are exactly those who consider RF, or anything Maxwell related, black magic.
I, and others, on this thread managed to realize not only how removed from understanding the basic tenet of electronics many involved with it are, but how recalcitrant they are to even try to. And this is alarming.
P.S.
I removed only the technical parts from my previous posts. I left all that remained.
This post has been shortened and cleansed to avoid upsetting other children.
Whatever was written here can be found in one or more of the following books (in no particular order, and without mentioning the usual suspects Feynman, Purcell, Griffiths, Ohanian, Jackson):
Kip
Fundamentals of Electricity and Magnetism 2nd ed
Lorrain, Courson
Electromagnetic Fields and Waves 2nd ed
John Kraus
Electromagnetism 2nd to 4th ed
Ramo, Whinnery, VanDuzer
Fields and Waves in Communication Electronics 2nd or 3rd ed
Panofsky, Phillips
Classical Electricity and Magnetism 2nd ed
Bleaney
Electricity and Magnetism 3rd ed
Nayfeh, Brussel
Electricity and Magnetism
Yes, engineers are inherently recalcitrant, they usually need to be because electronics engineering is more of an applied practical science than a theoretical science. Most practical practicing engineers rarely dive into the deeply theoretical world, they just use practical tools like Kirchhoff's to get the job done.
What would Bob Pease do...
So, ignoring Maxwell's equations has nothing to do with being practical. It is just an incapacitating feature. Deciding whether it is worthwhile learning them is a matter of choice.
Just pointing out that most practical engineers need not concern themselves with Maxwells equations (esp in a case like this) and this whole debate is all but pointless to any practical engineer. They'll just happily continue to use Kirchhoff's to make practical stuff that works, and just go "meh" to Lewin's academic argument (in this case). And there's nothing wrong with doing that, horses for courses.
I have not followed this whole thread, so I don't know about your arguments that Electroboom's claims are 100% bullshit, but I suspect that this isn't such a black and white case.
I don't think anyone doubts that Lewin is ultimately right (he is), but AFAIK he failed to address any of Electroboom's practical points.
From what I have seen, it's Lewin with his fingers in his ears repeating "KVL doesn't hold" 100 times, vs Electroboom trying to methodically evaluate the problem from a practical demonstration standpoint. From that I know who I have more respect for at the very least.
The difference of these two potentials is what we call the voltage difference, or simply the voltage V, so we have
V = −∫baE⋅ds = −∮E⋅ds.
But then you might say that the voltage is integral of E dl [i.e −∮E⋅ds] . Well, that's not true. Voltage is any energy per unit charge. Not just energy from electric sources. Hmm. Is that it? Does Dr. Lewin believe that voltage is only defined by electric forces?
So Dr. Belcher also concluded that Dr. Feynman himself and I have the same definition for voltage [...]
....
The half the whole tread is mostly just about being overly picky about the details and naming of things in physics. The thread did provide some interesting thought experiments along the way, but untimely things never got any closer to an agreement.
Circuit analysis (And that includes KVL) was never meant to be used to explain the underlying physics, but instead doing the opposite, made to abstract away any non vital parts of physics to let you focus on the operation of a circuit. If you apply circuit analysis the wrong way to your circuit then you get wrong results. Garbage in garbage out simple as that.
So if KVL is for the birds then the entirety of circuit analysis theory is for the bids as well. I'm sure any proper electronics engineer will disagree because circuit analysis has served them well ever since learning it in school.
So please circuit analysis for explaining circuits and not physics.
I also don't understand what Sredni was trying to accomplish by deleting content from his posts. Basically vandalizing his own work to make it harder for someone else to follow the tread.
I also don't understand what Sredni was trying to accomplish by deleting content from his posts. Basically vandalizing his own work to make it harder for someone else to follow the tread.
....
You continue to think being an arrogant intellectual bully who time and again resorted to petty name calling and demeaning anyone not totally agreeing with you is a credible Scientific or Engineering method. On any level and as I mentioned a long while ago would not be tolerated in most workplaces or institutions of learning.
In this thread is some great reading but so much useless non Science and Engineering and OTT Ego driven non debate.
Play the science and engineering not play the man!
Is that because I cared to study, read, read again, check, double check, watch Mehdi's videos more times than any of his own subscribes, watch Lewins videos the same number of times, just to ascertain the truth? Just because I don't want to forward misconceptions?
If you feel like others are really dumb, you are often not seeing something.
Social constructs can be difficult sometimes.
Wait a minute! Dave can say that he didn't follow the thread and that he doesn't respect Lewin based on mere impressions. I discussed the theme exhaustively, concluded, not decided, that Lewin deserves our respect and Mehdi doesn't and I am an arrogant intellectual bully?
Is that because I cared to study, read, read again, check, double check, watch Mehdi's videos more times than any of his own subscribes, watch Lewins videos the same number of times, just to ascertain the truth? Just because I don't want to forward misconceptions?
Am I a bad guy?
....
You continue to think being an arrogant intellectual bully who time and again resorted to petty name calling and demeaning anyone not totally agreeing with you is a credible Scientific or Engineering method. On any level and as I mentioned a long while ago would not be tolerated in most workplaces or institutions of learning.
In this thread is some great reading but so much useless non Science and Engineering and OTT Ego driven non debate.
Play the science and engineering not play the man!
Wait a minute! Dave can say that he didn't follow the thread and that he doesn't respect Lewin based on mere impressions. I discussed the theme exhaustively, concluded, not decided, that Lewin deserves our respect and Mehdi doesn't and I am an arrogant intellectual bully?
Is that because I cared to study, read, read again, check, double check, watch Mehdi's videos more times than any of his own subscribes, watch Lewins videos the same number of times, just to ascertain the truth?
Depends, 2 minutes ago I interrupted a conversation between my manager and a colleague to point out that they are trying to talk about how to put holes in metal work for wiring before we have even agreed the wiring (that i will have to design). Am I superior? yes I am! The world is full of dumb people that call themselves engineers because they do drawings. Doing drawings and designing are two entirely different things.
Kirchhoff's laws were meant to explain the underlying physics. Read Kirchhoff's original paper (https://gallica.bnf.fr/ark:/12148/bpt6k151490/f509.item) posted by seagreh. If you can't read German, cross the border and kindly ask an Austrian inhabitant to read it for you.QuoteSo if KVL is for the birds then the entirety of circuit analysis theory is for the bids as well. I'm sure any proper electronics engineer will disagree because circuit analysis has served them well ever since learning it in school.
Kirchhoff is for the birds means that Kirchhoff is not a fundamental law. Just that. Be prepared to see it being violated repeatedly. It just means that circuit analysis has its limits. It cannot be used for every kind of circuit. And you have to know when it is not applicable.
I bet SPICE didn't tell you that.QuoteSo please circuit analysis for explaining circuits and not physics.
Circuit analysis is physics.
I didn't attack people, an entire channel's audience, and members on this forum.
You make it sound like all this is so plainly obvious, that it's all obviously settled, and "how dimwitted Mehdi's audience is for not noticing this", that Mehdi " do not deserve our respect and should not be addressed as engineers".
Yet here you are saying that it took you all this effort to figure it all out watching the video countless times, reading, re-reading, studying, double checking etc ::)
And now we are simply take your word for it that this it's all settled and it's obvious Mehdi is completely wrong on every point etc, so much so that we shouldn't respect him as an engineer?
Sorry, but I'm going to play along with that.
This is not a trivial argument that even the most experienced and well educated engineers understand, in fact the argument has been going on decades.
Mehdi had every right to question Lewin's experiment, because without excruciatingly detailed investigation it seems like a dodgy setup to demonstrate his point.
And from what I can see there still seems to be debate on this forum about the exact applicability and implementation of the demonstration.
And from what I saw in Lewin's videos he didn't really even attempt to break down and explain why Mehdi is wrong.
Kirchhoff did not say
Σ Vk = 0
But he basically said, the sum of voltage drops (he expressed as product of resistance and current) equals to the sum of EMFs.
[...]nennen wir [...] die elektromotorische Kraft, die ihren Sitz in der Berührungsstelle dieses und des folgenden Drahtes hat, Ki [...]
[...] wenn die Drähte 1, 2, ...ν eine geschlossene Figur bilden,[...]
[...]so können wir diese Gleichung schreiben:
I1.ω1 + I2.ω2 + ... + Iν.ων = K1 + K2 ... + Kν
[...]wo, ω1, ω2, ... die Widerstände der Drähte, I1, I2 ... die Intensitäten der Ströme bezeichnen[...]
Now let's take the open secondary of a transformer, for example, comprised of a single turn. This experiment is very easy to reproduce with a linear transformer (I did that using a MOT).
Since the loop is open the current in the wire is zero. The EMF is 1V (my MOT can give me 600mV for a single turn). Applying Kirchhoff's law using exactly the terminology of his seminal paper we have:
an absurd.
Absurd indeed. - To apply Kirchoff's Circuit Law (Kirchoff's loop rule) to EMF source alone, w/o actual circuit or loop. :palm:
another absurd.
The difference between a purely electrostatic field and one induced by a magnetic field is the non conservative part. This gives the field ability to push electrons around closed loops of conductor while a electrostatic field can only redistribute them but not sustain a current apart from the very brief transient as they redistribute.
Since the inner conductor forms a continuous loop trough the voltmeter, it means that the the field can push the electrons around it and create a current that the voltmeter detects as voltage across its internal resistance. The shield however does not form a continuous loop and as such can't experience any current trough it.
I don't see why you would need current to shield a static electric field.Quote...My point is that the coax shield in this configuration has no effect.
I'm not convinced. I expect the coax will shield the center conductor from the induced electric field. So you would measure the same voltage whether the scope was on the left or the right side.
[edit] Correct equation is I1*R1+I2*R2+(-L(di/dt))=0.
OK, I'm convinced. I tried it. The coax doesn't do a damn thing.
You are right.
My new explanation, pretty much the same as yours, is the induced field component that causes the current is parallel to the wire. Putting a coaxial shield parallel to the field does nothing.
So even though there is no magnetic field in the region of the test leads, only the induced electric field, you can't shield them with only a conductive shield.
[edit] Correct equation is I1*R1+I2*R2+(-L(di/dt))=0.
Since i is constant in my example di/dt is zero (or next to it if you consider a very low current at a low frequency).
So I1*R1 + I2*R2 =0, 1V = 0V !!. The absurd remains the same.
But today is your lucky day. I'll show you how Kirchhoff fails once more. There are infinite ways to show that Kirchhoff doesn't hold. I could do this the whole day. It's a shame that I am not paid for that. Perhaps I'll open a Patreon account and ask people to help me debunk this pseudo scientific claim.
Anyway, in the circuit below I connect a battery, but if you don't like it, you can connect a generator, that produces the same voltage of the EMF. Of course the current is going to be zero. See what happens.
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=652575;image)
Faraday 3 x Kirchhoff 0
[edit] Correct equation is I1*R1+I2*R2+(-L(di/dt))=0.
Since i is constant in my example di/dt is zero (or next to it if you consider a very low current at a low frequency).
So I1*R1 + I2*R2 =0, 1V = 0V !!. The absurd remains the same.
So is then KVL in a quantum superposition of being dead and alive at the same time?
We all know you can't use KVL in varying magnetic fields, so why do you keep trying to prove it?
you simply put -1V in the equation: 0.1V + 0.9V - 1V = 0.
Before you talk about Maxwell equations, make sure you understand elementary physics.
you simply put -1V in the equation: 0.1V + 0.9V - 1V = 0.
You put -1V there and explicitly violates Kirchhoff' law.
You mistakenly think so because as you already demonstrated, you do not comprehend what di/dt and "current at the time of observation" means.
I am not sure that you fully understand conservative and non-conservative fields as well.
Any clue that they differ and you have to take in account all fields? Your original formula "I1*R1+I2*R2=0" did not include EMF, so I corrected it: I1*R1+I2*R2+(-L(di/dt))=0.
No, not at all. At least I hugely respect your work on studying, checking, and explaining; I believe others respect it as well.
All the namecalling (like the flat-earther shit), roasting inbetween is what people don't like. It's called "bullying". But I think you have been getting better during the thread. Try to keep on the subject, try to be less condescending, and you'll do fine. You are not superior. If you feel like others are really dumb, you are often not seeing something.
Social constructs can be difficult sometimes.
Even Lewin managed to apologize for an earlier video retort to Mehdi and if this socially flawed human can manage that there may be hope for you too.
A little rant to feed our thoughts.
....
Great video by Electroboom. Lewin is mixing models in wrong way.
In my humble opinion, The circuit laws apply only to pure sizeless graphs of lumped sizeless components connected with sizeless lossless equipotential wires conducting with infinite speed. Whole modeled circuit has total volume of zero cubic microns and completely electroneutral and disconnected from rest of universe. No fields of any kind are present.
What about transmission lines?
To me, an engineer professing pseudo-scientific claims (which is different from questioning), or advocating deficient knowledge as an advantage, especially at the expense of the reputation of another professional is morally appalling.
This is a total inversion of values. The savvy have to apologize to the ignorant for being savvy. Almost makes you discourage to seek knowledge.
You should never take my word for it. Go out and investigate for yourself. I learned those words with a famous video blogger which I really respect (exactly because of those words). Please feel free to check the video references, the references in Feynman's lectures. Draw your own conclusions. I'm just pointing things out (together with expressing my opinion, albeit not exactly popular, I can see it now).
What about transmission lines?
What about transmission lines?
Yep a transmission line is what is used to model that travel time in lumped circuits. The actual implementation of a transmission line probably varies a bit, but for simulators you usually specify a characteristic impedance and propagation delay.
And yeah SPICE does not do any of the thinking for you. Its the users responsibility for giving it a accurate circuit model so you still need to know what you are doing. So why would spice be bad? Its just a programatical implementation of existing circuit analysis theory.
circuit simulators like EMTP (Electromagnetic's Transient Program).
You mistakenly think so because as you already demonstrated, you do not comprehend what di/dt and "current at the time of observation" means.
Well, I may not understand a lot of things, but you surely don't know the difference between an inductor and a generator. Please, read this (http://www.feynmanlectures.caltech.edu/II_22.html).
Although it would be nice to take credit for Kirchhoff's work and say that the formula is mine, we'd better not only attribute it to Kirchhoff but also not try to surreptitiously and clandestinely sneak "corrections" into it.
Who the hell is advocating for "deficient knowledge" as being an advantage?
You don't have to apologise for anything, no one has a gun to your head demanding that. But people are free to think of you and the way you express yourself in any way they like, including having a not so good opinion of you.
When you say that Mehdi "should not be addressed as (an) engineer", you aren't going to win many friends on here.
Not to mention calling Mehdi's audience "dimwitted"
Well lump modeling is used quite a bit in RF too.
The EM simulations of distributed element filters on PCBs or 3D filter structures can get very slow. So often the results of those simulations are converted into a lumped equivalent circuit that can then be used to run simulations quickly in efficiently with tools like SPICE while still behaving accurately.
Tho these sorts of equivalent circuits can become quite a bit mess of resistors inductors and capacitors and very few nodes in that cirucit have any actual meaning to the real life cirucit.
Most voltages and currents in these big complex lump models are just partial math results of something, its only the voltage across the terminals of the whole black box is the one that actually matches a real voltage in the real cirucit.
Its all about engineers being efficient with there time because they have to deal with things called deadlines.
@beefefees
You said you wrote the book ? What was the subject? I did not follow the drama, but it looks for me like the discussion about pedagogy. Not the scientific matters. Please do not be discouraged. The only problem I have observed was that there is good and bad way to deliver the knowledge. Quality of explanation matters. Students shall not be made confused.
Fair enough. I'm here because of your invitation to "anyone involved in electronics design" and because "This is where everyone hangs out and rants and chats about whatever electronics topics that don't fit into the other more specific categories on this forum."
So, here I am ranting like crazy about what I find to be wrong with the world when it comes to electronics. If I don't win friends or influence people (I have the book), at least I hope someone can learn something with it.
This thread has proved that if you don't understand the underlying physics of electromagnetism you'll be limited in your ability to design and analyze circuits.
Oh, you think that transformer (inductor with two windings) is generator? :palm:
Perpetum mobile formula of voltage drop on loads that does not include voltage source (EMF) is truly yours.
Do not disgrace Kirchoff, please.
QuoteIts all about engineers being efficient with there time because they have to deal with things called deadlines.
It's all about engineers knowing what they're doing. If you don't know what you're doing will never be efficient and will never meet any deadlines.
People are learning, and technical input like yours is always massively appreciated.
But unfortunately your approach has been somewhat abrasive (even for an engineering forum, were lack of tact and copious amounts of abrasion are commonplace) and I'm not surprised it's rubbed some people the wrong way. That was just inevitable with your approach.
This thread has proved that if you don't understand the underlying physics of electromagnetism you'll be limited in your ability to design and analyze circuits.
And this sentence proves without doubt, that bsfeechannel is not an electrical/electronics engineer or anything remotely similar. Here you have it, the Dunning–Kruger effect at work. It reminds me of Dr. Lewin solving his problem 34 :palm:
But look what I have to deal with.This thread has proved that if you don't understand the underlying physics of electromagnetism you'll be limited in your ability to design and analyze circuits.And this sentence proves without doubt, that bsfeechannel is not an electrical/electronics engineer or anything remotely similar. Here you have it, the Dunning–Kruger effect at work. It reminds me of Dr. Lewin solving his problem 34 :palm:
I don't think I have said something abrasive here. How do I reply to that?
This is not the first time this guy says this about me and he did it long before I said that Mehdi shouldn't be addressed as an engineer. He is not even molested by the moderation and he'll probably be even thanked by it.
So I'm really at a loss as to what are the acceptable limits for "abrasion" in this forum. :-//
I like to contribute, but it is really frustrating to be mocked for that when guys like this are free to troll at will.
This thread has proved that if you don't understand the underlying physics of electromagnetism you'll be limited in your ability to design and analyze circuits.And this sentence proves without doubt, that bsfeechannel is not an electrical/electronics engineer or anything remotely similar. Here you have it, the Dunning–Kruger effect at work. It reminds me of Dr. Lewin solving his problem 34 :palm:
I don't think I have said something abrasive here. How do I reply to that?
This is not the first time this guy says this about me and he did it long before I said that Mehdi shouldn't be addressed as an engineer. He is not even molested by the moderation and he'll probably be even thanked by it.
So I'm really at a loss as to what are the acceptable limits for "abrasion" in this forum. :-//
I like to contribute, but it is really frustrating to be mocked for that when guys like this are free to troll at will.
...
I like to contribute, but it is really frustrating to be mocked for that when guys like this are free to troll at will.
You better behave
Here's a dollar, kid. Go get yourself a better education.
His video is a crime against humanity.
Who is being arrogant, after all? Mabilde and all those who recalcitrantly refuse to learn, or Lewin who dedicated an entire life to teaching?
This stubborn attitude is what is getting under our skin.
So don't fool yourself. You're not doing science a favor. If you really love science do as we all do: humbly learn.
So, never try anymore to hide your lack of knowledge behind excuses like that. Convince yourself and others of the need to be ready to learn something new every day.
Oh, you think that transformer (inductor with two windings) is generator? :palm:
Where did you find a transformer in the circuit? There are only two wires connected to each other forming a closed figure. Exactly as Kirchhoff said it had to be.
Now let's take the open secondary of a transformer, for example, comprised of a single turn.
QuotePerpetum mobile formula of voltage drop on loads that does not include voltage source (EMF) is truly yours.
There is no voltage source in the circuit. Only two resistive wires.
The EMF is 1V (my MOT can give me 600mV for a single turn).
You said it is transformer:Now let's take the open secondary of a transformer, for example, comprised of a single turn.
You are making your own reality on the go:The EMF is 1V (my MOT can give me 600mV for a single turn).
Nope. This is a different circuit. It only has one wire and one EMF. The other one has two wires and no EMF where Kirchhoff said it should be.
Nope. This is a different circuit. It only has one wire and one EMF. The other one has two wires and no EMF where Kirchhoff said it should be.
Why would KVL say there is no EMF?
See this equation: http://www.feynmanlectures.caltech.edu/II_22.html#mjx-eqn-EqII2234 (http://www.feynmanlectures.caltech.edu/II_22.html#mjx-eqn-EqII2234)
Yep since KVL works in lumped circuits and attributes the voltage to an inductor while with Maxwell its just sums it in as a whole. Just two different ways of going about the same thing that come to the same result when used correctly.
So if you take yourself as being so knowledgeable in how to analyze circuits, have you decided yet what is the correct way to analyze the behavior of this circuit?
https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/msg2189216/#msg2189216 (https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/msg2189216/#msg2189216)
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=647828;image)
I can give a trip that gain degradation on the transistor plays no role in the operation so a ideal transistor with a fixed Hfe can be used, but the parasitic capacitance in the transistor are important to the operation, all of them are stated in the datasheet for that transistor (Tho a ballpark figure for most small signal transistors is close enugh)
The boxes are microstrip lines (see Dave's videos of spectrum analyzer teardowns). Does Kirchhoff's law apply?
How about not such an easy one:
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=656277;image)
The boxes are microstrip lines (see Dave's videos of spectrum analyzer teardowns). Does Kirchhoff's law apply?
What you are saying is equivalent to say: here is a silicon diode, does Kirchhoff's law apply? Or if you prefer: here is a transmission line, does Kirchhoff's law apply? Don't you have to put the element in a circuit first?
I was trying to show a circuit that obviously wasn't that simple.
Both of Kirchhoff's laws can be understood as corollaries of Maxwell's equations in the low-frequency limit. They are accurate for DC circuits, and for AC circuits at frequencies where the wavelengths of electromagnetic radiation are very large compared to the circuits.
You do not apply Kirchoff's law to circuits where current in the conductor is not uniform.
I was trying to show a circuit that obviously wasn't that simple.
Kirchoff's circuit Law do not apply to AC circuits that does not have DC circuit properties. Look at the input of that microstrip filter - for DC current it is dead short. The same about output.
Wikipedia explains it well enough (https://en.wikipedia.org/wiki/Kirchhoff%27s_circuit_laws):QuoteBoth of Kirchhoff's laws can be understood as corollaries of Maxwell's equations in the low-frequency limit. They are accurate for DC circuits, and for AC circuits at frequencies where the wavelengths of electromagnetic radiation are very large compared to the circuits.
Other way to say it:You do not apply Kirchoff's law to circuits where current in the conductor is not uniform.
As for the statement "You do not apply Kirchoff's law to circuits where current in the conductor is not uniform": what if you define a Gaussian surface surrounding the conductor with non-uniform current (or any part of a circuit by that matter) and compute the integral of all the currents crossing the surface? You'll find that the integral is zero; same as Kirchoff's current law!
In this case Kirchoff's circuit law does notholdapply, sorry.
As for the statement "You do not apply Kirchoff's law to circuits where current in the conductor is not uniform": what if you define a Gaussian surface surrounding the conductor with non-uniform current (or any part of a circuit by that matter) and compute the integral of all the currents crossing the surface? You'll find that the integral is zero; same as Kirchoff's current law!
I did not mean skin effect but transmission line effect - current uniformity trough the length of the circuit/loop. Sorry about wording.
Example: Speed of electric impulse in the cable (velocity factor) is ~65...85% speed of light. We just pick 195000 km/sec figure. So we have battery, lightbulb and 195km cable (twisted pair) to connect both. When we connect battery to the cable, current trough battery is flowing immediately but lightbulb is not lit yet, current will start to flow trough it (only) after 1ms. In this case Kirchoff's circuit law does notholdapply, sorry.
The reality is that RF engineers simulate circuits with all those components. Those simulators rely on KVL and KCL, and they work. There is no argument here beyond semantics.
Kirchhoff holds | Lump-modelling possible | Implication | Comment |
True | True | True | Every circuit for which Kirchhoff holds can be automatically lump-modeled. |
True | False | False | If you're saying that you can't lump-model a circuit where Kirchhoff holds you're contradicting the line above. So, false. |
False | False | True | If you find a circuit that is impossible to lump-model then Kirchhoff doesn't hold (Lewin's circuit). |
False | True | True | Kirchhoff doesn't hold, but you can still lump model the circuit under certain conditions. Feynman picture 22-9 (http://www.feynmanlectures.caltech.edu/img/FLP_II/f22-09/f22-09_tc_big.svgz) |
So for the 195km cable you can model it as a before mentioned 4 port device to lump the entire cable. Then Kirchhoffs circuit laws work again as they always work in fully lumped circuits.
If you want to say Kirchhoff's laws can't be used in circuits with transmission lines
then you must say they can't be used in circuits with inductors, transformers and capacitors.
Sure you are right - *IF* you model cable as a string of many lumped elements. Engineering is exact science and circuit of my oversimplified example contained three elements: 1) battery 2) cable 3) light bulb. That was whole point of example - to show case where you can't apply KVL and what's even more important - *why*. No need to cheat to get around pre-requirement for KVL I was illustrating. During described 1ms you can't apply KVL but later when current is uniform through the loop, KVL appies.
Second, a very long 'cable' is far from an ideal conductor. Similarly, a battery is far from an ideal source. Finally, a light bulb is far from an ideal resistor.
Assuming you have idealized 'real' components and then proclaiming that KVL can not be applied is a straw man fallacy.
Sure you are right - *IF* you model cable as a string of many lumped elements. Engineering is exact science and circuit of my oversimplified example contained three elements: 1) battery 2) cable 3) light bulb. That was whole point of example - to show case where you can't apply KVL and what's even more important - *why*. No need to cheat to get around pre-requirement for KVL I was actually illustrating! During described 1ms you can't apply KVL but later when current is uniform through the loop, KVL appies.
Hopefully you did not get sick with "putting unsaid words into debate opponents mouth disease", diagnosed for some here in this thread? ;)
Yep since KVL works in lumped circuits and attributes the voltage to an inductor while with Maxwell its just sums it in as a whole. Just two different ways of going about the same thing that come to the same result when used correctly.
So if you take yourself as being so knowledgeable in how to analyze circuits, have you decided yet what is the correct way to analyze the behavior of this circuit?
https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/msg2189216/#msg2189216 (https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/msg2189216/#msg2189216)
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=647828;image)
I can give a trip that gain degradation on the transistor plays no role in the operation so a ideal transistor with a fixed Hfe can be used, but the parasitic capacitance in the transistor are important to the operation, all of them are stated in the datasheet for that transistor (Tho a ballpark figure for most small signal transistors is close enugh)
I'm guessing those loops are supposed to form a transformer and the circuit is an oscillator? So we replace the loops with a lumped transformer? I'm trying to read your mind, maybe not successfully.
The other way to read the schematic is a wire is a zero length connection in a netlist, so that circuit doesn't do much.
Hopefully you did not get sick with "putting unsaid words into debate opponents mouth disease", diagnosed for some here in this thread? ;)
Did i claim that a user said something? If so then that was not the intention sorry.
I have built the circuit for real on the bench and built it in LtSpice. Worked fine in both cases.
I'm just looking forward to how bsfeechannel explains how one should analyze this circuit correctly since all of it is inside the so called "KVL dies here" zone. So if classical circuit analysis theory supposedly can't be used here, then there must be some other way to calculate its behavior.
Second, a very long 'cable' is far from an ideal conductor. Similarly, a battery is far from an ideal source. Finally, a light bulb is far from an ideal resistor.
Assuming you have idealized 'real' components and then proclaiming that KVL can not be applied is a straw man fallacy.
Components are ideal until it is explicitly said that they are not. As you are not on the same page and fail to comprehend whole idea of dumbed down example so generic public can understand described transmission line effects, I have nothing to further discuss with you.
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=647828;image)
Berni, may I ask what is the resonant frequency of your circuit? Also, what would happen if you put a piece of metal close to the loops? I am asking because your circuit could make a fine metal detector...
Berni, may I ask what is the resonant frequency of your circuit? Also, what would happen if you put a piece of metal close to the loops? I am asking because your circuit could make a fine metal detector...
I think the real circuit ran at about 17MHz while in spice somewhere around 21MHz. Tho i was using just a regular passive scope probe so the capacitance of it has likely affected the frequency too. As one might expect putting a lump of ferrite in there does drag down the frequency slightly. Haven't tested if non ferrous metal around the coil affects it, i would guess not since that doesn't change the inductance, just introduces extra loss in the form of eddy currents, large enough aluminium plate could probably stop the oscillator if it sucked away enough power from the coil.
Could probably also be used as a weak CW radio transmitter, but the waveform is not a sinewave and is not even symmetrical so there would be plenty of even and odd harmonics, but the power is really low as the whole circuit only uses 1 or 2 mA from the power supply.
As soon as you say a 'cable' is 195 km long it stops being ideal. Forget about modeling it using the telegrapher's equation, just the fact that the resistance per meter will accumulate to a value significantly larger that the load after such length, renders your example as useless.
Second, a very long 'cable' is far from an ideal conductor.
My understanding is that non ferrous metals should decrease the inductance, therefore increasing the resonant frequency. Anyhow, nice simple circuit with useful practical applications... Did you use magnet wire? What gauge? AA battery?
It does not need to be ideal. I just picked long enough line to bring timing into intervals most will not be afraid of. If I would talk about > 2GHz frequencies and according wavelengths, many would not understand how transmission lines work, what is velocity factor. "Telegraphers equation" indicates that you do not understand transmission line physics as well.
It does not need to be ideal. I just picked long enough line to bring timing into intervals most will not be afraid of. If I would talk about > 2GHz frequencies and according wavelengths, many would not understand how transmission lines work, what is velocity factor. "Telegraphers equation" indicates that you do not understand transmission line physics as well.
Really? I would recommend you some enlightening reading from chapter 10 of "Engineering Electromagnetics" by William H. Hayt and John A. Buck where the figure below comes from:
What exactly you imply by pointing to this common model of transmission line? - That you understand it contrary to my trolling? :D If you understand - good for you.
Even if 195 km twisted pair line is built using copper conductor, it does not make my example useless as you say. After all battery voltage nor light bulb current were specified. By arguing about nonessential properties of my oversimplified example you are just wasting electronic ink of internet and to be honest - making yourself fool.
Non-essential properties you say! Go tell that to the electrical engineers of your local power utility and watch their reaction. If reading the book I recommended is out of your reach, try watching a PBS documentary from the series American Experience about the first trans Atlantic cable. I think YouTube has it.
Non-essential properties you say! Go tell that to the electrical engineers of your local power utility and watch their reaction. If reading the book I recommended is out of your reach, try watching a PBS documentary from the series American Experience about the first trans Atlantic cable. I think YouTube has it.
Instead of offering me read that book maybe you can read it yourself? Please show me how transmission line DC resistance property relates to what I was talking about in my example? You may start with velocity factor formula and check where you put DC resistance in. Anywhere?
(https://wikimedia.org/api/rest_v1/media/math/render/svg/8554ab053195511103518ae463e6c7b52ad5136a)
[edit] It does not add to the discussion about wavelengths in the cable if you are trolling about how big attenuation will be in 195km cable or how hugely expensive it will be. It does not matter in the context!
Your example is fundamentally flawed because you failed to properly model the elements of the circuit before attempting to analyzed it.
Indeed sorry - that many including you, ignored or missed purpose of my "195km transmission line" example: to illustrate how transmission line works and how it can be that current is not uniform trough the length of the circuit/loop. Obviosuly to apply KVL, we have to do something with that line - either lower working frequency or use it's lumped elements model.
When you model all the elements of your circuit correctly then Kirchoff's laws do work!
If he did then you and a couple of others wouldn't have had to have spent, what, maybe a hundred or two man-hours trying to break this down and debate and explain it?
This is not a trivial argument that even the most experienced and well educated engineers understand, in fact the argument has been going on decades.
Mehdi had every right to question Lewin's experiment, because without excruciatingly detailed investigation it seems like a dodgy setup to demonstrate his point.
I don't think anyone doubts that Lewin is ultimately right (he is), but AFAIK he failed to address any of Electroboom's practical points.
From what I have seen, it's Lewin with his fingers in his ears repeating "KVL doesn't hold" 100 times, vs Electroboom trying to methodically evaluate the problem from a practical demonstration standpoint. From that I know who I have more respect for at the very least.
Lewin: In the case of an induced EMF the potentials in a circuit are no longer determined, they depend on the path
You make it sound like all this is so plainly obvious, that it's all obviously settled, and "how dimwitted Mehdi's audience is for not noticing this",
Professor X is saying I cannot walk on water. But here I am, walking on grass. See? I can even jump and run. Walking is very useful, a lot of runners walk and run every day. Professor Y and Z agree with me.
QED.
However we need to express our appreciation for Simon's work. I've been a moderator before. It is one of the most ungrateful tasks, let me tell you.
I also don't understand what Sredni was trying to accomplish by deleting content from his posts. Basically vandalizing his own work to make it harder for someone else to follow the tread.
Yep, I don't get it either, all that hard work gone, but we've seen this before on the forum and it usually doesn't end well unfortunately. I hope that doesn't end up being the case here.
I've benefited from your contributions Sredni. I've been silently following the conversation here (I just registered so I could comment) but I actively participated in the Youtube conversations on both EB's and Lewin's channels. I was the person who reminded Lewin about the Romer paper which he mentioned in one of his response videos (he credited me by my YT moniker).
As a matter of fact I've used this very discussion as a teaching example in my lab classes on electric motors and power electronics. I've made it a point to remind the graduating seniors of electrical engineering that Maxwell's Equations are the Laws of Classical Electrodynamics and have used the Romer-Lewin Ring paper and demonstration as a pointer to that fact.
It's a good thing our technological progress is governed by hard mathematics and experiment, otherwise we would still believe that objects of different masses fall at the same rate, because believing otherwise violates our 'intuition.'
By the way, it's easy to demonstrate that fact even without a vacuum chamber. Put a tiny sheet of paper on top of a textbook and drop them both.
Anyways, Lewin was/is correct and has been all along. :-+
The TS100 has a massive installed base of fanboys that have been pestering me for a year now to basically validate their purchase for them.
While each of us have developed an intuition about how the world works, it's very important to remember that this intuition only applies to a very limited set of conditions. For instance, there's absolutely no reason to expect that matter will act the same in the center of the sun as it does here on Earth on a bright and sunny day. However, that last statement is hard for some people to accept and, judging by my email inbox, the extreme realm that causes people the most difficulty is what happens when things are going super-fast.
Shahriar: We are at an age where information is free, right? This is pretty much the first time in human history, where you have access to the to the entire collective human knowledge in the palm of your hand. This is an astonishing outcome of our ingenuity, but at the same time what you also have in the palm of your hand is an unlimited set of misinformation, so what is the skill you need? Right? Thirty years ago you needed the skill to know things. Now you need the skill to know how to put things apart. That's the skill you need. So, but, are we teaching that? [...] But, if you don't teach people how to sort through information, in an information age, then things get out of control, because then you have no idea how this is going to turn out. And then we see effects of that in the world.
Dave: And people are susceptible to uh more powerful people who wanna take advantage of that fact, that people don't know how to sort out.
Shahriar: I mean it becomes so easy, right? And the issue with this is that any piece of information put on line especially in social media, social media is just, I mean, we use social media all the time, so, you know, we're bashing exactly the thing we're using, but at the same time it's such a disaster, because every piece of information that shows up, especially a person's ignorance, is just as valuable as a scientist's input, because there's no way to discern them, if you don't know how to discern them.
Dave: But it's not just that, because you can put true, you know, incontrovertible data in front of someone and they still won't believe it.
Shahriar: That's a whole other issue is that people... In order for you to change your mind about something that you fundamentally hold dear is that you have to make an emotional sacrifice because you have to abandon something you sure relied on and that can be difficult and that can be hard and more importantly you have connected with other human beings who share your point of view and now you're all of a sudden alone if you let go of that idea. [...] [P]eople build communities around information which may be false ultimately.[...]
On the ModerationQuote from: bsfeechannelHowever we need to express our appreciation for Simon's work. I've been a moderator before. It is one of the most ungrateful tasks, let me tell you.
I'm sorry but there's no room for appreciation for sloppy work and for the incongruent justification he gave for my ban. I could go into details, but it is clear from what he did and wrote that feedback is something to print on T-shirts and that's it. So, why waste time? He probably does not even know how his messages are rendered by browsers outside the one he uses (or that when one is banned there is no way to send PMs).
But I want to add something to explain why I deleted the technical part of my last posts and, since the thread is now dead, to address what I see as the real problem in the Lewin-Mehdi discussion. I won't get into the physics, it's not worth the time spent.Quote from: BerniI also don't understand what Sredni was trying to accomplish by deleting content from his posts. Basically vandalizing his own work to make it harder for someone else to follow the tread.Quote from: EEVBlogYep, I don't get it either, all that hard work gone, but we've seen this before on the forum and it usually doesn't end well unfortunately. I hope that doesn't end up being the case here.
What do you expect? Me going Turbo and try to kill princess Vanellope?
Nah, I simply decided not to contribute to this blog anymore than it is necessary to get my potential future questions answered. You had someone who could provide content (and believe me, I had a lot more material to share), now you have a leech.
I removed only the technical parts from my previous posts and left all that remained because I still had the curiosity to know what earned me a ban (apart from Simon to be a precog, as postulated by ogden), but it's clear that that curiosity is going to remain unanswered. Since I did not see anything in particular, I deduced that what irked the guy who reported 'the topic was getting heated' was the technical part. So I removed it. Yeah, a waste of work and time, much in the same way the time and work I had put in my last post (on when it is desirable to contain the whole field) was wasted due to the ban.
If the people who manage the site don't care, why should I?
Technically this was post 1 of 3, but I posted it as last because, you know, when it is not clear why you guys ban people, one never knows when their 'hard work' can go wasted.
For those of you that keep defending Dr. Lewin's 'superior' understanding of circuit theory, please take a look at its series of videos about problem #24: 'Circuit with 5 resistors':
...
Now, tell me what is wrong with 'his' approach at solving such a simple circuit.
For those of you that keep defending Dr. Lewin's 'superior' understanding of circuit theory, please take a look at its series of videos about problem #24: 'Circuit with 5 resistors':
...
Now, tell me what is wrong with 'his' approach at solving such a simple circuit.
He presented a correct solution in the first 5 minutes of the second video. He used mesh analysis with three loops. (Which of course involves KVL).
Then he mistakenly thought he had a very clever way of doing it with two loops. He got the right answer but had wrong assumptions and drew some wrong conclusions. So all the rest of the videos are his admitting he made a mistake and explaining what he did wrong.
So he made a mistake, and then corrected it. Not a great reason for bashing him.
Nope. The issue is more fundamental than that.
Nope. The issue is more fundamental than that.
Care to explain?
Nope. The issue is more fundamental than that.
Care to explain?
Sure thing; thanks for asking!
Dr. Lewin is using mesh analysis and making a big fuzz about 'his' solution that results in only two equations and two unknowns. This compared to the 'brute force' method that yields three equations and three unknowns. What Dr. Lewin doesn't seem to know is that if he uses nodal analysis he'll end up with the minimum number possible of equations and unknowns. Always. The difference in efficiency and simplicity is so significant, that mesh analysis should be only used in the simplest of circuits; those with only one or two meshes. Unfortunately it seems to me that mesh analysis is the only method taught in physics courses.
I'm not sure nodal analysis always results in the fewest equations and unknowns. For example, this circuit I think has 9 meshes, but 11 nodes, not counting the three corner nodes:
Unfortunately it seems to me that mesh analysis is the only method taught in physics courses.
Yeah there are indeed many ways to tackle solving this.
Just that the mesh analysis with loops requires the least knowledge to apply. The same exact thing is done for every section of the circuit and and all of the currents pop out as a result.Tho as the circuit gets bigger and more complex the system of equations can start getting unreasonably large for calculating by hand (I always kept a graphic calculator around for solving these automagicaly).
Have you seen this video about KVL/Faraday's law and non-conservative field?
https://youtu.be/pUsdiIl1Kyg
1) elp - iR = 0 violates Kirchhoff's law, because Kirchhoff is adamant about stating that the EMF (elp) has to happen along the path of the circuit at a different place where the voltage drops occur.
Here we go again :palm:
All the wire of Lewin's circuit is EMF source, thus "wiring" is zero length point where EMF-generating wire is connected to resistor. Resistors are infinismall as well - because their dimensions are *not* specified.
You agree that there is actual voltage drop on the resistor (IR) that is equal to EMF voltage created in the loop (elp), yet you say that elp - iR = 0 is bullshit.
Come one... Before you decide to participate in the discussion about electromagnetic induction, make sure to learn fundamental laws of physics such as law of conservation of energy.
The wires in Lewin's circuit do have a length and so do the resistors. There's nothing "infinitesimal" /there.
Now it's up to you to discover how the conservation of energy holds for such a circuit (hint: Maxwell's equations).
Are you serious or just trolling?
I repeat: all the wire of the contraption is secondary winding, there's no "interconnection wire" that would not generate EMF.
So we assume that it's (connection wire) length is zero. It is there only in the circuit *schematics*, not in real world.
Dr.Lewin ignores EMF voltage generated *in* the resistors, so he ignores their dimensions, so they are assumed as zero.
Is it so hard to comprehend?
Could you explain please? For simplicity there is single 1Ohm resistor, EMF is 1V, 1A is flowing for 1 sec. Please consider equation in form: power_generated - power_dissipated_in_the_resistor = 0.
2) The voltage on an impedance is ONE no matter how you measure it.
Impedances are measured where there's no varying magnetic flux, so the way you measure it counts.
QuoteCould you explain please? For simplicity there is single 1Ohm resistor, EMF is 1V, 1A is flowing for 1 sec. Please consider equation in form: power_generated - power_dissipated_in_the_resistor = 0.
Before we can address this problem, let's suppose that we live on a planet
That's a new one in this thread that i don't agree in.
2) The voltage on an impedance is ONE no matter how you measure it.
Impedances are measured where there's no varying magnetic flux, so the way you measure it counts.
Why would the impedance of a passive component change in the presence of a magnetic field? The component is still passing current in the same dependence to voltage as before it was placed in a field, since this very dependence is called impedance means the impedance has not changed. If you measured it being different in a changing field then your measured quantities are likely affected by the field (Since impedance is measured indirectly from other quantities) rather than the impedance being affected.
That is unless you make your resistor out of a material that shows significant magnetoresistive effects. But as far as i know pure copper or carbon based resistors don't have any significant magnetoresistive properties. Even then they would react to DC fields too, not only AC fields.
QuoteCould you explain please? For simplicity there is single 1Ohm resistor, EMF is 1V, 1A is flowing for 1 sec. Please consider equation in form: power_generated - power_dissipated_in_the_resistor = 0.
Before we can address this problem, let's suppose that we live on a planet
Yes, we live on a planet. It is a fact. Are you going to explain conservation of energy using Maxwell's equations or not? Your usual goalpost shifting tactics is not funny anymore, you shall stop it.
Besides I'm really busy. So I'm outsourcing my reasoning to your brain and the experiment I proposed can be easily performed right here on earth. If you don't know where the extra energy comes from, just say it, there's no shame about that.
QuoteWhy would the impedance of a passive component change in the presence of a magnetic field? The component is still passing current in the same dependence to voltage as before it was placed in a field, since this very dependence is called impedance means the impedance has not changed. If you measured it being different in a changing field then your measured quantities are likely affected by the field (Since impedance is measured indirectly from other quantities) rather than the impedance being affected.
An impedance is Z = V/I. If you're under a varying magnetic field, the voltage will be dependent on the path. So the way you measure this voltage will affect the value you get for your impedance. In extreme cases, as Feynman points out, the varying magnetic field overcomes all the internal reactions and the component becomes a generator, which is not an impedance anymore.
Under a varying magnetic field an impedance can not only change depending on the path, but also cease to be.
Which means that, if you want a "stable" impedance, you have to measure it away from any varying magnetic fields, at its terminals, defined by Feynman as the region where you have no varying magnetic fields.
In that case the component you are describing is no longer just a passive component.
So then could you please explain how would you measure the impedance of a real battery? (Hence it has internal resistance that can't be directly mesured) Lets also put the battery in a place where there are no magnetic fields present, so in that case we should get only one impedance value as a result, right?
Impedance is a constant coefficient of proportionality between V and I. It is in general complex number and a function of frequency. Can we talk about a constant coefficient of proportionality between voltage and current of a battery?
Answer my question and half of the explanation you want about Maxwell will be answered, requiring only to adapt the formalism.
Before we can address this problem, let's suppose that we live on a planet where g = 10 m/s². We lift an object of 1kg from the ground up to 1m. The potential energy transferred to this object will be U = mgh = 1kg*10m/s²*1m = 10 joules. If we drop down this object, when it hits the ground the potential energy will be converted to kinetic energy, which will be exactly 10 joules. Energy is conserved.
Now let's suppose that we live on a planet where g can vary. We lift the same object to a height of 1m with g = 10m/s² as before. But as soon as we drop the object, g suddenly becomes 20m/s². When the object hits the ground the kinetic energy will be 20 joules.
Where did this excess energy come from?
Energy was added to the system by one who brought extra mass to the planet.
Now please stop playing challenge games and be so kind - explain law of conservation of energy using Maxwell's equations. I am looking for equation in form: power_generated - power_dissipated_in_the_resistor = 0.
So then what is the correct procedure for measuring the impedance of this battery from its terminals? You can also give acual numbers in each step since all of the batteries properties are defined with values in the paragraph above.
QuoteNow please stop playing challenge games and be so kind - explain law of conservation of energy using Maxwell's equations. I am looking for equation in form: power_generated - power_dissipated_in_the_resistor = 0.
Alright. Google for Poynting's theorem. Or go directly to chapter 27 of volume II of Feynman's lectures. Good read.
Is a battery a component of an AC circuit? Do you understand in what context we can talk about impedances? If you are in doubt I recommend you read the title of chapter 22 of Feynman's lectures, Volume II.
So do we get a method for measuring impedance of a battery? Or is such a thing impossible to do?
bsfeechannel and ogden you should meet and drink a beer together.
I guess after some time you will agree, probably only after just the first beer.
Yes batteries are perfectly valid in AC circuits because AC current is capable of flowing trough them. It just doesn't have any frequency dependence. Just like a resistor.
I never found any mention in that particular Feynman lecture about impedance not being applicable to components that act the same in AC and DC.
So do we get a method for measuring impedance of a battery? Or is such a thing impossible to do?
Poynting's theorem does not explain anything about resistor. Please come back to earth from your arrogance heights and explain w/o sending to google. Others reading this... khm... debate could be interested in **your** wizdom as well.
[edit] Ok..
As energy generated by wire loop is equal to energy dissipated in the resistor, we conclude that at any instant moment of time power delivered by wire loop is equal to the power dissipated by resistor. Now we will express what I just stated using equation: L(di/dt)*I = R*I^2. Do you agree?
Then we divide it all by I:
L(di/dt) = R*I
It results in what I was looking for,
L(di/dt) - R*I = 0
So do we get a method for measuring impedance of a battery? Or is such a thing impossible to do?
It is possible or not - depends on convenience of your debate opponent.
He takes sentences and words out of context, twist meaning as he pleases to suit his agenda of combative debate. Example: I say "Dr.Lewin does not account for EMF voltage generated *in* the resistors", his argument is that Dr.Lewin said: "EMF cannot exist in the wires, but only, and only, in the resistors". Dr.Lewin did not say that resistors generate EMF, he said that EMF generated by the loop of wire can be observed on the terminals of resistor. Absolutely different meaning, but hey - most readers of this thread will not even notice, right? :-DD
Here is the whole model with all values:
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=708420;image)
If you want it in that form you can take the battery voltage as being V(t)=1.5 + 0*ei*0*t. If such a thing is impossible then feel free to chose different numbers at your liking, can get rid of the DC component too if you think it matters. If a load needs to be placed across the output that is also fine as long as you specify what the load is.
What to measure is this: Whatever quantity you claim is impedance across the output terminals as a numeric value.
In the case the impedance at DC does not have a value, please explain the reason for it.
The answer is: it is not possible to measure the impedance across the terminals because this is not an impedance. You see, the voltage V and the current I won't establish a constant proportion, which is a requisite for considering anything an impedance.
Connect your ohmmeter to this battery and see what it indicates.
You can however try to determine an equivalent circuit as I showed in the Reply #886, on 18 February (https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/msg2208588/#msg2208588).
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=655911;image)
And the problem arises from the fact that we simply do not have an inductance there. The adage that any piece of wire is an inductor is a myth. A piece a wire can be an inductor under CERTAIN circumstances with which this piece wire does not comply.
If I show you the equations you don't understand.
The adage that any piece of wire is an inductor is a myth.
It's impossible to reason on pseudo-scientific assumptions because they lead you inevitably to contradictions. So, before we can answer anything we need to check if we are not talking nonsense.
Makes sense.
How about if the voltage of the battery is indeed a sine wave with no bias, defined as:
V(t)=1.5*ei*6,28*t
Is there an impedance then?
Btw i am interested in what exactly are these certain circumstances when a piece of wire suddenly gets the properties of inductance and when it does not.
You clearly have issues.
Anyway thank you, I will try harder :D
Problem with your reasoning is that I was not explicit about material of wire or magnetic core or absence of it. Ok, fine. Forget about inductor. - You apparently have problems to fathom not only non-conservative versus conservative fields, but true power versus reactive power as well. Let's assume that variable magnetic field just happens and it induces 1V EMF in the loop, EMF equals (eip). Now what is *correct* (mine was incorrect as you say) equation that shows law of conservation of energy between wire loop and resistor? Just try me and produce equation even if in doubt that anybody except you will understand it.
Dr.Lewin ignores resistance of wire - it is scientific and accepted by you.
When I say that EMF generated in the (by the) resistors are ignored by Dr.Lewin - just because dimensions of resistors are ignored as well, you say it is pseudoscience and nonsense |O
Take a moment and look from different angles on what I just said.
Nope. I regret to tell you. The voltage will be defined by the "battery" and the current by whatever load you connect to its terminals, so there won't be a fixed coefficient of proportionality between the amplitude of the voltage and the amplitude of the current.
You can try to calculate or measure it.
QuoteBtw i am interested in what exactly are these certain circumstances when a piece of wire suddenly gets the properties of inductance and when it does not.
Glad you asked. Take a linear transformer. The secondary of a transformer will be a piece of wire wound around some core, be it air or whatever. But to simplify our reasoning, let's suppose that the core is vacuum.
Well, a piece of wire wound around a core? You say. It is an inductor, isn't it? Of course it is. Take whatever LCR meter you have and connect it to the terminals of this secondary and it'll confirm that.
You can even calculate and measure its impedance for whatever frequency you want. |Z| = |V|/|I| = 2πfL.
Now connect the primary to a voltage source. A voltage will appear at the terminals of the secondary, won't it? But wait a minute, nothing is connected to the secondary, so the current is zero. If I take this voltage and divide it by the current I will have |Z| = |V|/0, which is undefined.
Don't pull your hair out yet. Suppose that I now connect a resistive load. The resistor will force the current to be in phase with the voltage. The same current that is traversing the wire of the secondary. But in an inductor shouldn't the current be lagging the voltage by 90°?
Yet you have a coiled piece of wire where you have an alternate current in phase with the voltage at its terminals. So much for our inductor!
So, how can it be? What changed from the condition where the primary was disconnected to when it was connected? Certainly it was not the wire, because we haven't touched it. Something else must be producing this change.
What is it?
So then back to the original question. Under what circumstances is a wire not an inductor and when it is? Or does only self inductance count? If not then at what coupling factor (k) does it stop counting as an inductor? 0.5? 0.1? 1E-6?
Since it starts with an F, it is Michael Faraday!
You say, the EMF is generated IN the resistor ! Hmmm. The resistor being the seat of EMF? You are sure?
Imagine a super-conductive ring with a single tiny 10k resistor inserted.
You say the EMF sits in the resistor. Now, removing the resistor, would remove the EMF as well ? Or does the EMF now jump into the air gap. Can vacuum as well be a seat for EMF?
Let‘s assume the EMF sitting in the resistor. Wouldn‘t it then compensate with the voltage drop within the resistor - the resistor being a closed system with energy sourcing part and energy dissipating part in itself? Wouldn‘t this result in 0V at the resistor terminals ? Actually fitting the 0V along your superconductive ring ?
As I said before, many pople have hard times to understand the difference between EMF and voltage drop!
And maybe Kirchhoff could help you here :-)
As you read his original paper, you must have seen, Kirchhoff‘s intention was not to summarize whole complete world and ‚zerorize‘ it! He simply summed up voltage drops on one side of the equation and summed up EMFs on the other side of the equation. There was no zero in his equation. Now, EMFs on the right side could be coulomb EMFs and non-coulomb EMFs (e.g. Faraday‘s - dPhi/dt).
Hence Prof. Sam Ben-Yaakov is right -
EMF (being -dPhi/dt) = iR (being the line integral of E dl).
Left side of the equation being the energy sourcing part (EMF) being equal to energy consuming part (right side).
bsfeechannel and ogden you should meet and drink a beer together.
I guess after some time you will agree, probably only after just the first beer.
In forums it's easy to escalate for no real reasons.
Conventionally today the voltages (emfs or voltage drops) found in the circuit are placed to the left of the equation. To the right is the account of the effect of induction. If there's no induction, all the voltages add up to zero and KVL holds. If there is induction, the voltages will add up to the calculation indicated by the right side, and Kirchhoff doesn't hold anymore.
The calculation to the right side is not a voltage that you'll find in the circuit (as Prof. Ben-Yaakov confirmed), which means that you cannot conventionally place it to the left side as if you'd find that with your voltmeter. This is simply stupid. (And it is even "stupider" to look at the zero left to the right of the equation after this mathematical bodge and declare because of this that Kirchhoff holds.)
In fact, none of the (duly debunked) "debunkers" of Lewin managed to measure this voltage in any of their circuits.
Νot even this unfortunate professor.
In fact, none of the (duly debunked) "debunkers" of Lewin managed to measure this voltage in any of their circuits.
The resistor happens to be where the EMF is. If you remove the resistor, the EMF stays in the same place. You don't need a superconductor to prove this. Just connect a voltmeter to the secondary of a transformer capable of providing a sufficiently large current. Then connect a 10k resistor. The voltage won't change.
2) The assumption that if a mass has more kinetic energy when it hits the ground than it's gravitational potential energy MUST mean someone doubled the mass of the planet. :o
I admit that last one made me chuckle.
Now let's suppose that we live on a planet where g can vary. We lift the same object to a height of 1m with g = 10m/s² as before. But as soon as we drop the object, g suddenly becomes 20m/s². When the object hits the ground the kinetic energy will be 20 joules.
You say, the EMF is generated IN the resistor ! Hmmm. The resistor being the seat of EMF? You are sure?
Absolutely sure.QuoteImagine a super-conductive ring with a single tiny 10k inserted.
You say the EMF sits in the resistor. Now, removing the resistor, would remove the EMF as well ? Or does the EMF now jump into the air gap. Can vacuum as well be a seat for EMF?
The resistor happens to be where the EMF is. If you remove the resistor, the EMF stays in the same place. You don't need a superconductor to prove this. Just connect a voltmeter to the secondary of a transformer capable of providing a sufficiently large current. Then connect a 10k resistor. The voltage won't change.
QuoteNah, I simply decided not to contribute to this blog anymore than it is necessary to get my potential future questions answered. You had someone who could provide content (and believe me, I had a lot more material to share), now you have a leech.
That's a shame. But you are the one who deleted all your posts, not us.
We do care that you removed your content, that's a real shame. But it's you who made that decision, I hope you are not accusing us of somehow forcing you to do that?
When people are banned their posts are NOT deleted, so no "hard work" is lost, the content still remains for others to enjoy, learn from and discuss. You and you alone decided to delete all your posts and your hard work.
But I did not see any explanation for my ban, except for the one I assumed.
That is, puncturing the ego of someone who DID NOT QUALIFY AS A MODERATOR (to me that was some bloke cracking a joke, and I treated him as such), and made no specific requests as to what we should have done. Stop posting? Saying the counterpart was right? Take a bow?
I did your experiment. At the begin of the experiment the EMF must have been in the air gap between both secondary terminals.
However, as soon as I connected the voltmeter, I got the feeling the EMF jumped into my voltmeter
(as it is 10MOhm resistive. As you say EMF is path dependent).
With the 10k resistor I was expecting it to sit now in the Voltmeter AND in the resistor at the same time - according to your thesis.
And I always thought, the EMF is defined as the tangential force per unit charge in the wire integrated over length, once around the complete circuit/loop! But not at all, it was hiding in the resistor and my voltmeter!
But you confused me a bit later, when talking about the [elp]. The [elp] being the EMF (I guess the Israeli Prof meant [Epsilon loop] with this abbreviation). You tell me it’s invisible and can’t be measured? Although you told me before it’s sitting in the resistor and how to measure it?
On the other hand you say today’s convention is to put voltage drops AND EMFs on the left side. But insist at the same time to keep the -dFlux/dt on the right side? -dFlux/dt being the EMF.
Looks like you don’t consider -dFlux/dt as EMF, but rather the EMF as part of the line integral E ds?
Once you measure the voltage on the 10Mohm of your meter or the 10kohm load, you won't find this voltage anywhere else in the circuit. All that you'll find is a wire with (ideally) zero volts.
You'll understand electromagnetism sooner than those who thanked you.
All that said, let me add that I have no hard feelings toward the site. As a matter of fact, apart from this 'incident', I believe it's one of the most relaxing places where to talk about electronics.
But the moderator screwed up, and you lost a contributor.
I am still leeching, tho.
This was exactly my point. It doesn't make sense to talk about a voltage source as purely being an impedance.
When analyzing the circuit it makes more sense to think of it as an equivalent circuit. This separates the voltage source from the impedance part, allowing both to remain the same no matter the load.
Or is the use of equivalent models somehow forbidden in circuit analysis?
What you describe is called mutual inductance in circuit analysis. As soon as inductors start sharing magnetic fields they also start sharing there inductance too.
Here is a quick summary of how this works: https://physics.stackexchange.com/questions/119638/choosing-sign-for-kvl-mutual-inductance
So now how does the transformer secondary not have 90 degree phase shift if its an inductor? Because the voltage is all coming from mutual part of inductance and this inductance only cares about the current in the primary.
The current trough the load resistor actually affects the voltage of the primary side.
Once all of these currents and voltages are summed up neither the primary or secondary have 90 degree phase shifts anymore. In an ideal 1:1 transformer with no leakage the currents and voltages are actually all perfectly in phase (If the load is a resistor like in your example) or 180 out of phase depending on what way around you connect the coil.
All my hair is still in its place as there is no need to pull it out over a concept that works just fine, or is the use of mutual inductance somehow forbidden?
So then back to the original question. Under what circumstances is a wire not an inductor and when it is?
:-DDSince you rejected my baby-stepped method for guiding you to enlightenment, I'll be forced to reveal the shocking truth to you. The conservation of energy holds for when Kirchhoff fails because the energy the resistor is dissipating comes from the fuh...., the fuh-fieh..., the fie... No, I can't. I can't put you through this emotional sacrifice. I have scruples.
Right. Be prepared to become enlightened.
Right. Be prepared to become enlightened.Since you rejected my baby-stepped method for guiding you to enlightenment, I'll be forced to reveal the shocking truth to you. The conservation of energy holds for when Kirchhoff fails because the energy the resistor is dissipating comes from the fuh...., the fuh-fieh..., the fie... No, I can't. I can't put you through this emotional sacrifice. I have scruples.
Again you show that you can't even read :palm:
I did not ask to tell where energy comes from. I ask you to show law of conservation of electrical energy using Maxwell's equations. Apparently you are afraid of what comes next after you do it.
Since you don't want to know where the energy comes from, it'll be impossible for you to understand it using Maxwell's equations, or whatever.
Yes exactly my point that a voltage source is not an impedance.This was exactly my point. It doesn't make sense to talk about a voltage source as purely being an impedance.
A voltage source is NOT an impedance, much less "purely". Read Feynman lectures volume II chapter 22.
...
What determining the equivalent circuit of a battery has to do with measuring an impedance in an AC circuit under a varying magnetic field?
...
So what causes the change in their behavior is the _ _ _ _ _.
...
As you confirm, not only the secondary doesn't behave like an inductor (there's no 90 degree phase shift), but also it is not even an impedance: because the voltage on the secondary is a function of something external to itself, which is in fact the _ _ _ _ _ generated by the current in the primary.
...
How can this be, once the primary is connected to a voltage source?
...
So now not even the primary can be identified as an inductor anymore.
...
Forbidden? Why? It perfectly demonstrates what I said before: if you don't understand the underlying physics of electromagnetism you'll be limited in your ability to design and analyze circuits.
...
If you read your own words again you'll see that you've already answered your question.
Today at 08:42:17 am » Insert Quote
You are ignoring this user.
Do not confuse public forum with private chat, tell for those who you think will understand.
To cut the crap: KVL is based on conservation of the charge which is based on law of conservation of energy.
As soon as you write energy_generated_inthe_loop = energy_dissipated_inthe_resistor equation, KVL can be derived from it.
Energy conservation in electromagnetism is a little bit more complicated (http://www.feynmanlectures.caltech.edu/II_27.html), and can be derived, as in the case of conservation of charge, from the modified (by Maxwell) Ampère's law, however you need to understand that the energy that's powering the resistor is not coming from a component in the circuit.
Let's start with charge conservation, which is easier for a circuit-head guy like you to understand. You can find it demonstrated here (https://en.wikipedia.org/wiki/Maxwell%27s_equations#Charge_conservation).
In the picture below you can see how KCL fails, but charge conservation holds.
(https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/?action=dlattach;attach=713982;image)
The sum of currents going in and coming out of the volume represented by the closed dashed line to the left is different from zero, violating KCL. But conservation of charge holds because the excess charge is being stored in the body inside the volume.
I dont see how charge is conserved inside the dotted circle. Curent is charge divided by time anyway.
I dont see how charge is conserved inside the dotted circle.
Curent is charge divided by time anyway.
But yeah i can see what the point is, an example of KVL not holding. We KNOW that KVL is not a law of physics.
It holds in most cases but not all,
QuoteBut yeah i can see what the point is, an example of KVL not holding. We KNOW that KVL is not a law of physics.
Kirchhoff studied carefully the behavior of currents and voltages in circuits and published the results of his findings in the "Annals of Physics". Then he derived his theorems, as he called them, from those empirical data. His discovery was a major breakthrough.
So KVL and KCL ARE laws of physics. But a law of physics has not to work under whatever condition. As important as it is to understand KVL and KCL it is to know when they hold and when they fail.QuoteIt holds in most cases but not all,
I would say that KVL and KCL do NOT hold most of the times. Where can you find a place on earth where you don't have varying electromagnetic fields? The thing is that we PRETEND that KVL and KCL hold by approximation. We stash fields inside capacitors and inductors, we create ground planes, employ shielded conductors, we decouple lines, inductors, capacitances, all to avoid having to deal with fields. And when we have to deal with them, we employ rules of thumb and equivalent approximate models.
And what we cannot tame and make to conform to KVL/KCL we call "parasitics".
This creates the illusion that KVL and KCL hold "in most cases". But it's only an illusion. Not that we will abandon this illusion all of a sudden. We need to know what it means, and not to try to linger to it if it clearly shows that we will be limited in our ability to interpret the phenomena around us.
As important as it is to understand KVL and KCL it is to know when they hold and when they fail.
I would say that KVL and KCL do NOT hold most of the times. Where can you find a place on earth where you don't have varying electromagnetic fields? The thing is that we PRETEND that KVL and KCL hold by approximation. We stash fields inside capacitors and inductors, we create ground planes, employ shielded conductors, we decouple lines, inductors, capacitances, all to avoid having to deal with fields. And when we have to deal with them, we employ rules of thumb and equivalent approximate models.
And what we cannot tame and make to conform to KVL/KCL we call "parasitics".
As I said before, scientific populism is going to be a big problem a few yeas ahead.Opinion based decisions are surely a problem (and i am guilty of making them myself), but anyway, science teaches to check your results, so "scientific populism" is an oxymoron - "pseudoscience" would be the word. Science also teaches that the observation of a process might interfere with the result (and therefore needs taken care of).
It's just next fallacy of yours. Those two round objects on the left together form charged capacitor and wire between them - load where energy that is stored in the capacitor, dissipates. KCL holds.
Wird ein System von Dräten, die auf eine ganz beliebige Weise mit einander verbunden sind, von galvanischen Strömen durchflossen, so ist:
1) wenn die Drähte 1, 2, ...µ in einem Punkte zusammenstoßen,
I1 + I2 + ...+Iµ = 0,
wo, I1, I2, ... die Intensitäten der Ströme bezeichnen, die jene Drähte durchfließen, alle nach dem Berührungspunkte zu als positiv gerechnet;
So why do we still use Maxwells equations if they are wrong according to Quantum electrodynamics? Its much like the reason why we still use Kirchhoffs circuit laws despite being wrong according to Maxwell.
On a macroscopic level and under certain conditions these laws still work just fine, while being much more convenient to work with when you want to actually calculate them with actual numbers. The 3 sets of laws are basically just different abstraction layers for electricity. Just chose the desired abstraction level and be aware of its known limitations.
Tho to be honest there is very very little reason to go any deeper than Maxwells level of abstraction for engineering use.
I dont see how charge is conserved inside the dotted circle. Curent is charge divided by time anyway.
He most likely did mean that charge is distributed evenly between two round objects. Yes, it is so - if there is separate point of reference (ground?) to measure voltages/charges of both round objects. In such case we have two capacitor paradox (https://en.wikipedia.org/wiki/Two_capacitor_paradox) which again agrees with KVL.
We have just one wire, with just one current.
This problem is analogous to the KVL problem: we have just one voltage, and no other to balance it that can be directly measured in the circuit.
It's just next fallacy of yours. Those two round objects on the left together form charged capacitor and wire between them - load where energy that is stored in the capacitor, dissipates. KCL holds.
In case you insist that there is just one wire and just one current meaning no path for return current - then I say that you don't even have circuit, thus Kirchoff's Circuit Law do not apply. There is huge difference between "do not apply" and "do not hold".
so those two round objects together indeed is capacitor, C=q/V.
Sorry, my wording was wrong, I should have said ‘I always believed, the EMF...’.!QuoteAnd I always thought, the EMF is defined as the tangential force per unit charge in the wire integrated over length, once around the complete circuit/loop! But not at all, it was hiding in the resistor and my voltmeter!
You clearly thought wrong, I regret. EMFs will never "hide" inside (static) wires (considered as ideal, that is).
This phenomena is well known in literature as the ‘One-Wire-Single Current-Sophism”.
Let's examine KCL in the words of Kirchhoff himself (https://gallica.bnf.fr/ark:/12148/bpt6k151490/f525.item):QuoteWird ein System von Dräten, die auf eine ganz beliebige Weise mit einander verbunden sind, von galvanischen Strömen durchflossen, so ist:
1) wenn die Drähte 1, 2, ...µ in einem Punkte zusammenstoßen,
I1 + I2 + ...+Iµ = 0,
wo, I1, I2, ... die Intensitäten der Ströme bezeichnen, die jene Drähte durchfließen, alle nach dem Berührungspunkte zu als positiv gerechnet;
Translation
Let a system of wires, which are connnected with each other in an entirely arbitrary way, be traversed by galvanic currents [i.e. DC], then:
1) if the wires 1, 2, ...µ meet at one point,
I1 + I2 + ...+Iµ = 0,
where, I1, I2, ... designate the intensities of the currents, which flow through each wire, all calculated as positive in the direction of the point of contact;
We have just one wire, with just one current. This problem is analogous to the KVL problem: we have just one voltage, and no other to balance it that can be directly measured in the circuit.
Sorry, my wording was wrong, I should have said ‘I always believed, the EMF...’.!QuoteAnd I always thought, the EMF is defined as the tangential force per unit charge in the wire integrated over length, once around the complete circuit/loop! But not at all, it was hiding in the resistor and my voltmeter!
You clearly thought wrong, I regret. EMFs will never "hide" inside (static) wires (considered as ideal, that is).
Because the clearly wrong ‘thought’ is from Feynman Volume II chapter 16 Induced Currents.
As you say, electromag is so unintuitive, so much bullshit around.... you can’t even trust books anymore.
This phenomena is well known in literature as the ‘One-Wire-Single Current-Sophism”.
For sure, can only be solved with Maxwell equations :clap:
Maybe you missed the point, the ‘connection point’ (Berührungspunkt)?
Hence, a single wire hitting the connection point is a dead end, hence I1 = 0 .
Yes exactly my point that a voltage source is not an impedance.
In that chapter 22 that you mention it clearly shows that induced voltage acts like a voltage source. So including the induced voltage when calculating impedance of a component is just as nonsense as directly calculating the impedance of a voltage source using the voltage across its terminals.
2 terminal components can't have multiple impedance at the same moment in time.
is there any reason why you replaced the world field with underscores?
Its not exactly a secret that magnetic fields are what makes inductors work.
Exactly it doesn't behave like an inductor anymore, but instead behaves like a coupled inductor.
But it doesn't mean its inductance simply disappeared. The same magnetizing current is still needed to hold up the field, but because the two inductors are sharing the same flux means they can also share the magnetizing current. Since the resistor on the secondary can't provide a source of reactive current means that all the magnetizing current comes from the voltage source on the primary. The resistive load does however cause a in phase current that makes a opposing field in the secondary that affects the field in the primary, where it induces voltage according to Faradays law. Since there is a voltage source forcing a well defined voltage across the primary, this instead draws extra current to correct this field. This extra in phase current is what drags the total current back away from lagging 90 degrees. As for the secondary, it has no need for out of phase current, because all of its magnetizing current is provided by the primary.
So the inductance didn't go anywhere. The effect of inductance is simply buried under the other currents.
So yeah, sorry i still don't see the exact circumstance when a piece of wire stops being an inductor. Or does becoming a coupled inductor not count as being inductive? If so please explain why.
So why do we still use Maxwells equations if they are wrong according to Quantum electrodynamics? Its much like the reason why we still use Kirchhoffs circuit laws despite being wrong according to Maxwell.
Kirchhoff's laws are not wrong according to Maxwell. Maxwell's equations do not only confirm that KVL and KCL are right, but also state in WHAT CONDITION they are right.
The source of the errors is elsewhere.
QuoteOn a macroscopic level and under certain conditions these laws still work just fine, while being much more convenient to work with when you want to actually calculate them with actual numbers. The 3 sets of laws are basically just different abstraction layers for electricity. Just chose the desired abstraction level and be aware of its known limitations.
A cat is a special case of mammal, and the description of a mammal is an abstraction of a cat (and every other mammal, as a matter of fact).
QED is an abstraction of Maxwell's equations, as Maxwell's equations are abstractions of KVL/KCL.
KVL/KCL are a special case of Maxwell's equations, as Maxwell's equations are special cases of QED.
KVL/KCL are NOT abstractions of Maxwell's equations by the simple fact that they don't work for all the cases for which Maxwell's equations do.
This is another illusion. Because we ram KVL/KCL down the throats of our circuits and close our eyes to the errors due to this approximation (and we manage to get away with it in many cases) we have the impression that KVL/KCL are just simplified (hence abstracted) cases of Maxwell's equations. But this mindset will bite you in the butt sooner or later. You need to be always aware of the limitations of KCL/KVL and, if the error due to approximating Maxwell to Kirchhoff is gross enough, resort to what will give you the most accurate prediction.
QuoteTho to be honest there is very very little reason to go any deeper than Maxwells level of abstraction for engineering use.I think the inventors of the transistor would not agree with you, but anyway...
In case you insist that there is just one wire and just one current meaning no path for return current - then I say that you don't even have circuit, thus Kirchoff's Circuit Law do not apply. There is huge difference between "do not apply" and "do not hold".
Nope. Kirchhoff says clearly that the wires can be connected in an entirely arbitrary way. So there is no requirement for them to form a circuit or to provide a path for a return current.
Yes the source of the error is people like Dr. Lewin applying it directly to a circuit without consideration if its applicable in those CONDITIONS.
Fix those conditions by properly modeling the thing as a circuit mesh,
if not then forget about Kirchhoffs circuit laws and stick to Maxwell.
Okay yes i was using more the software engineering definition of abstraction layers rather than the mathematics definition of abstraction. With the mathematics definition it is indeed the other way around.
And i fully agree, all of the levels of explaining electricity work fine as long as you use them within those limitations. Hence why i never really had any problems applying KVL to Dr. Lewins experimental circuit from his lecture. Any paradox between KVL and Maxwell with that circuit is simply down to using them wrong.
I'm pretty sure QED had nothing to do with the development of the first transistors.
Then the first working BJT device popped up by ]accident from a bunch of people trying to build a better solid state RF mixer.
The usual transistors can still be explained rather well with Maxwells fields pushing charged particles around.
Mostly just a case of controlling where the charge carriers are rather than making use of any quantum mechanical effect.
I'm pretty sure very few forum members here work in a semiconductor fab, let alone one that works with such fine feature capabilities or work on building quantum computers. Hence why very very few engineers would have a good reason to dig deeper than Maxwell, heck for 95% of cases even Kirchhoff is close enough(As long as you know about the other 5%).
Exactly. Kirchhoff says "wires", thus more than single wire you desperately insist on. When you have single wire - you do not have conditions to apply KCL.
That's why I looked for return current which I BTW found in the "spatially distributed capacitor",
Alright. I created an ogden version of KCL fail for you.
Quoteif not then forget about Kirchhoffs circuit laws and stick to Maxwell.The problem with your reasoning is that you think that if things are connected like a circuit, then Kirchhoff MUST hold. You think that if you find a single circuit where it can't be employed to explain its behavior then the whole theory is cactus.
This is BULLSHIT.
There are circuits for which Kirchhoff holds and others for which it doesn't. By now you should have known the difference. And the difference is that if the circuit is drenched with a varying magnetic field, KVL is out. If not, then you can merrily use your KVL and your precious LTSPICE to model it.
Lewin's circuit, if you have not paid the due attention to it yet, is just a sophisticated version of Faraday's original demonstration of induction. Lewin is just reenacting the same experiment with two fancy oscilloscopes and two resistors of relative high value. But the experiment is essentially the same.
Saying Lewin is wrong is the same as denying Faraday's law.
QuoteAnd i fully agree, all of the levels of explaining electricity work fine as long as you use them within those limitations. Hence why i never really had any problems applying KVL to Dr. Lewins experimental circuit from his lecture. Any paradox between KVL and Maxwell with that circuit is simply down to using them wrong.We've already showed that your "modelling" just don't apply to Lewin's circuit. It introduces gross errors. If I connect the lead of MY voltmeter (not yours with 250mV in series with the probes) from one resistor to the other where a wire should be in your "model" I will measure 0.5V, whereas in Lewin's circuit this voltage is zero, and everyone measured exactly zero volts.
There can't be any paradox between KVL and Maxwell. Lewin changed the condition for the validity of KVL and invited his students to explain the new behavior of that circuit. Those that think that Kirchhoff applies to just about any circuit are trying to find each one a different explanation. While those who understand Faraday's law could explain what is going on immediately.
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Wow! Shockley, Bardeen and Bratain won the Nobel Prize by accident! Lucky bastards!
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Isn't this what essentially QED is: electrodynamics applied to subatomic particles like the electron?
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Strange. I had the impression that electrons received and emitted photons when they change their quantic levels of energy in the electronic band structure.
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I also had the impression that every electronics engineer around the world learns at least some rudimentary concepts of QED as part of their regular course which is required to understand solid state electronics. But I may be wrong.