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
How does a transformer work? By applying Faraday. Not Kirchhoff, Faraday. I have a closed path, it defines an area. Let's do it!
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:
We've got this:
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?
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
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
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?
What would Jesus do?Well, 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.
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