Author Topic: Does Kirchhoff's Law Hold? Disagreeing with a Master  (Read 61062 times)

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Offline ogden

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #225 on: November 23, 2018, 03:10:56 pm »
Sredni, seriously? If you did not watch video, here's screenshot from it. Pay attention to EMF equation of loop4 and what loop4 actually is.  And watch the Funny video! Also reading Romer's paper will not hurt BTW.

 

Offline ogden

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #226 on: November 23, 2018, 03:50:28 pm »
He overall main mistake is that for some reason he thinks voltage must exist across the wire portion of the induction loop.

Here we go AGAIN. Groundhog Day (1993) movie. Why don't you read the forum first? Read Romer's paper as well.
« Last Edit: November 23, 2018, 04:10:43 pm by ogden »
 

Offline Siwastaja

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #227 on: November 23, 2018, 04:40:15 pm »
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.

It's also interesting how new accounts pop up in the EEVblog forum just to write such passive-aggressive "taking side" comments like this.

Thank you for your analysis, though.

If I needed to side with someone, it would definitely be Mehdi, regardless of who is being "right". One is clearly encouraging scientific engineering process (which includes questioning, experimenting, and desire to understand), while the other is actively hurting the process (by scaring, denying proper discussion, generally being a total asshole). I understand there are fanboys for the both "cultures".

Luckily, no one is forcing anyone to "side with" anyone.
« Last Edit: November 23, 2018, 04:49:14 pm by Siwastaja »
 
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Online Berni

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #228 on: November 23, 2018, 08:36:32 pm »
It's not KVL, it's Faraday.

Yes he got his results with Faradays law. But to prove that KVL is wrong he shows that the voltages don't add up to zero. Voltages adding up to zero is KVL and he was applying it to a circuit model that is not valid in normal circuit analysis methods where KVL is meant to be used. This is his proof before saying its for the bids.

Just like usual Newtonian kinetic energy equation ( E = (m*v^2) / 2 ) breaks if you are approaching the speed of light since that form of the equation works with the assumption that speed of light is infinite or that Einsteins relativity effects don't exist, yet we don't say that Newton is for the birds. It works when used correctly


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.

Lumped model still works with the voltmeter inside the loop, you simply have to recalculate the values of the inductors that represent wire segments so that they match the crossection contribution and you again get accurate results from a lumped model. You can use an inductor to represent a fractional turn in order to model just one section of wire around the loop. If you want to know whats going on in the middle of that section of wire then simply split it into two half valued inductors and you get a node with the voltage and current at that point in the loop.

The lumped model does not make it necessary to put all the inductance in the loop inside one inductor. This inductance can be split over as many inductors as you want to expose the voltage and current at any point along a wire. It may seam strange to have this fractional turn section of wire since Faradays law requires a loop, but it does work and can be imagined as taking a slice of cake out of the loop and attributing that slice to its accompanying length of wire.

You have the freedom to construct a lumped model in a way that makes the desired measurements easy to access while not changing the behavior of the circuit.


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.

Sorry if that was misunderstood. I was mostly using it as an example of how quickly and often lumped component models sneak up when doing math with electricity. These lumped models have there own set of limitations, just like KVL and all other circuit analysis tools. It makes sense to use a resistor symbol, but you have to realize that it does introduces "lumpynes" into the model.


Lewin's circuit IS A CASE WHERE A LUMPED MODEL IS INAPPROPRIATE.
How can this be so hard to grasp?

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

It uses the above described "slice of flux cake" way of determining inductance values for sections of wire. Due to the lumped model it makes KVL work perfectly fine in it and allows any other circuit mesh analysis tool to be applied to it correctly.

Can you explain why a lumped model is inappropriate given that it is required in order to apply KVL to it?



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! :-)

Well that's because so far nobody has shown me what exactly i am doing wrong in my lumped model linked above. It reproduces the same waveform as Dr. Lewins experiment and does not have any cherry picked or tweaked component values in it.

I am not saying you have to analyze everything non lumped. But if you want to use KVL correctly you need to do it lumped.

If someone thinks this model is a lucky fluke i can also show it adjusted to probe other points on the loop or put the voltmeter inside the loop.
 
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Offline Sredni

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #229 on: November 23, 2018, 11:18:31 pm »

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

I will answer to this part only, because I cannot repeat the same things over and over again. Forgive the use of capital letters, but at this point I want to emphasize the message.

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.
All instruments lie. Usually on the bench.
 
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Offline sectokia

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #230 on: November 24, 2018, 12:08:38 am »
I was wrong.

Lewin is the fraud.

« Last Edit: November 24, 2018, 01:07:33 am by sectokia »
 

Online Berni

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #231 on: November 24, 2018, 12:19:40 am »
Your model DOES NOT BEHAVES IDENTICALLY to Dr. Lewins experimental circuit.

My circuit model produces a graph identical to what what Dr. Lewins two oscilloscopes show, so in what way does it behave differently to the real 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.

So how do you get a real life voltmeter to show you two different voltages at the same time? (Without flipping wires around as that effectively connects the voltmeter to a different part of the cirucit)

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.

I do actually agree to all of that. KVL doesn't have to account for inductance, or even resistance, other circuit analysis tools do it so it doesn't have to. You indeed can't mess with fluxes because they don't exist in lumped models so no worry there. And finally SPICE will indeed always give one voltage, that's why i like it, its always nice to get a concrete answer to a question.



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.

I sure hope i don't see SPICE giving two voltages, i don't like bugs in my software.

I completely agree with you that the nodes in Dr. Lewins have two different voltages across it according to the formal definition of voltage. I even explained it in one post how that works on the level of electrons and fields in a wire.

But do try to understand circuit analysis and lumped circuits a bit better. Then you will see how KVL indeed works when applied correctly (And no it still won't give you two voltages because the "effective voltages" used in circuit analysis always have exactly one value unlike "formal definition voltages" that Maxwell operates with).

So when do i get to see a real life voltmeter showing two voltages?
 
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Offline ogden

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #232 on: November 24, 2018, 12:42:24 am »
The voltage across the meter reads 0V.
This video at 9:30 shows this experimentally:

Indeed it shall read 0V between A&D points - if both resistors are equal (100 Ohms in this case). BTW thank you for providing video which at 12:30 confirms discussed in this thread behavior of the circuit - that actual voltage between A&D in Dr.Lewin's experiment is 0.4V.
 
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Offline sectokia

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #233 on: November 24, 2018, 12:53:20 am »
I was wrong.

Lewin is the fraud.
« Last Edit: November 24, 2018, 01:07:50 am by sectokia »
 

Offline Sredni

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #234 on: November 24, 2018, 01:07:36 am »
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.
All instruments lie. Usually on the bench.
 

Offline joeqsmith

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #235 on: November 24, 2018, 02:30:13 am »
So when do i get to see a real life voltmeter showing two voltages?

 :-//  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.   
How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
 

Offline rfeecs

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #236 on: November 24, 2018, 02:55:16 am »
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
 

Offline The_Paya

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #237 on: November 24, 2018, 03:08:03 am »
Quote from: rfeecs on Today at 13:55:16
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?
Edit: NVM.
I was wrong.

Lewin is the fraud.
-. wherever you go, there you are .-
 

Offline sectokia

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #238 on: November 24, 2018, 05:28:39 am »
We can all agree that meter probe when completely off to side reads -.1v and  when off the other side completely reads 0.9v.

If the meter probe comes down through the magnetic field splitting it exactly in to two halves of equal area  it reads 0.4v.

You can get any value you want from -0.1 to 0.9 by changing the ratio of the left and right area formed by the meter probes cutting the magnetic field.

You can attach the meter  directly across the left resistor and read anything from -0.1 to 0.4,  it depends solely on the ratio of the two areas that the meter probes cut the solenoid field into.

The same is true when putting the Probes across the other resistor in the other side.

The same is true when putting the probes on any point between the resistors to any point between the resistors on the other side.

In all those cases you can arrange the probes to read anything from  -0.1 to 0.9V.
 
I can connect 3 meters across the resistor on the left and have one read -0.1v, one read 0.4V and one read 0.9v.
« Last Edit: November 24, 2018, 06:27:49 am by sectokia »
 
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Offline bsfeechannel

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #239 on: November 24, 2018, 06:06:47 am »
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

Nice try. But why did he take half an hour to measure the voltage of a single loop connected to two resistors? Because he had to go into long considerations about Faraday's law of induction before he measured the voltages the "right" way.

Well, if you have to use another theory to validate yours, it means that your theory is not as fundamental.

Make no mistake. Kirchhoff is cool, but for flux sake, learn the doggone Maxwell. There you gon' understand Kirchhoff and much more.
 
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Online Berni

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #240 on: November 24, 2018, 10:17:45 am »
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.

Sure you can exclude the flux in the lumped model if you want. All you need to do is set the voltmeters wires to have 0 Henrys of inductance.(This makes the circuit impossible to construct in real life tho). I chose to include the flux so that it does behave like Dr. Lewins real circuit.

Nope not a shifting goalpost. You asked to see a lumped model show two voltages different across two points, voltmeters show this same "effective voltage" as used in lumped circuits so to have two voltages in the same point a voltmeter needs to show two different readings simultaneously too.

You make the different voltages show by changing the path of the wires. The model does the same by simply updating its probe wire inductance values to match the new wire path. Both get the same result on the voltmeter. So how are these results different?


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>

That video does a great job of explaining what is happening. To top it off all of his claims have an accompanying experiment to prove it, rather than just saying "This is how it is, chose to believe it or be wrong"


:-//  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 did the experiment a few days ago just because i thought it would be interesting, but i haven't posted photos since there ware no unusual results, it works the same as Dr. Lewins experiment as expected.
 

Offline HackedFridgeMagnet

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #241 on: November 24, 2018, 11:10:02 am »
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
Great video.  Well worth watching.

He uses a much, much better experimentation methodology and gives much better explanation of what is happening than Dr Lewin does.
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".
 
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Online Berni

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #242 on: November 24, 2018, 11:48:01 am »
Here are the photos of my recreation that i did last week but never posted photos. I still had it set up so i just cleared the bench a bit and made some photos and scope captures.

I used a MOSFET driver circuit i had laying around to pulse the current to the coil using a waveform generator so that i had a repeatable waveform with a trigger signal. The recreation of the experiment was mostly done because i thought it was a cool experiment and i don't get to play with such magnetic effects often.

Results are identical to Dr. Lewins experiment and are identical to my lumped circuit model ( https://www.eevblog.com/forum/chat/does-kirchhoffs-law-hold-disagreeing-with-a-master/msg1945312/#msg1945312 ) that i have put together before even doing the experiment.


So my conclusions stay the same:

1) Faradays law works and does show two different voltages across two points in a circuit. The two voltages appear because we are calculating only one section of the whole loop, what voltage you get depends on what loop section you are going along (The whole voltage is path dependent). There indeed is -0.1V and 0.9V across A and B in Dr. Lewins cirucit, but these are voltages along a incomplete loop (Probe wires complete it into a closed loop to then produce a single result on the voltmeter). Its more of a math technicality and NOT something like Schrodingers cat(Being both dead and alive simultaneously) where both voltages are somehow physically existing in two forms. Its only as real as imaginary numbers.

2) Kirchhoffs voltage law works too. When applied to a lumped circuit mesh representing the real circuit it shows the sum of voltages is zero and makes a prediction that matches Dr. Lewins experiment. Note that the lumped circuit includes the probe wires as part of the circuit (Dr. Lewins application of Faradays law does not include probe wires, hence why it does not fit together)

3) Dr. Lewin is right about everything in his videos except his claims about KVL are wrong. He is applying KVL incorrectly to his circuit. It should instead have been said that KVL is a circuit analysis tool and like all other such tools requires a circuit mesh model to work on (This model includes probe wires). Additionally KVL is defined as being "algebraic sum of all the voltages around any closed loop in a circuit is equal to zero" this is not the same as an integral of the electric field around the loop as he writes it, you require lumped components to be able to apply the summa operator() in the equations of KVL

4) Electroboom is technically wrong about bad probing since Dr. Lewin was measuring the voltage he set out to measure. However he recognizes correctly that the probing method is where the double voltage phenomenon comes from and has shown the underlying reasons for why. There are indeed some minor aspects of his video that could be improved, but he comes to the correct conclusion that KVL always works when used correctly.

4) This is a difficult to explain topic and its very hard to make an explanation that everyone understands.


I would love to see a 3 minute video that carefully condenses the information and explanation from this thread, but i am not a youtube creator.
 
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Offline bsfeechannel

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #243 on: November 24, 2018, 03:59:49 pm »
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.
 

Offline ogden

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #244 on: November 24, 2018, 04:19:24 pm »
He credits someone called Kirk McDonald for his explanation of the "Lewin paradox".

Good read BTW: http://www.hep.princeton.edu/~mcdonald/examples/lewin.pdf

3) Dr. Lewin is right about everything in his videos except his claims about KVL are wrong.

He is wrong in other claim as well - that 1/2 of the (superconductive) loop has no EMF and potential difference voltage drop between points A1 & A2 at the moment of observation is 0V (video: "Kirchhoff's Loop Rule Is For The Birds", @3:40). This assumption is kinda naīve as properly noted by Dr. Kirk McDonald.
« Last Edit: November 24, 2018, 04:27:29 pm by ogden »
 

Offline bsfeechannel

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #245 on: November 24, 2018, 06:55:20 pm »
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.

I think I understand sectokia's rant. 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.

This kind of attitude, we've got to admit, is disgusting and will only make half-assed engineers of all of us.
 
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Offline HackedFridgeMagnet

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #246 on: November 24, 2018, 10:26:22 pm »
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.

I don't think anyone here ever said they doubted Maxwell-Faraday.

But from what I can see Dr Lewin has absolute confidence in it's predictions, to the point he thinks he can measure the voltage difference at one set of two points, twice (using a CRO) and get two different answers.
Whereas Cyriel Mabilde shows he only reads two different voltages, because of the different fluxes linked in the leads.
Cyriel Mabilde in doing this shows us how we can measure emf properly.  Incidentally he does it using a sinusoid instead of a transient to show the sign of the voltage better.

Then Dr Lewin goes on to conclude KVL is for the birds.
This is sensationalist rubbish. KVL is successfully used everyday.
The proof is you can easily apply KVL to his demonstration with predictable experimental results.
The predictable results shows KVL works in this case too. Quite a few people have.

 

Offline Siwastaja

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #247 on: November 24, 2018, 11:04:21 pm »
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.

Bullshit. sectokia's comment was directed to Mehdi specifically, in a clearly malicious manner; but Mehdi's not responsible for other "people" transforming the discussion into any "libel". He couldn't have been more appropriate, and to the point.
 
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Offline rfeecs

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #248 on: November 24, 2018, 11:07:46 pm »
In Cyriel Mabilde's video, he is claiming that Dr. Lewin says "there is no EMF in the wires".  He says this is wrong and that his measurements remove all doubt about the existence of EMF in the wires.

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.

When he makes his wedge shaped measurements, he is defining a surface outlined by the wedge.  That determines a quantity of magnetic flux through that surface, and that determines an EMF.  Obviously the EMF changes when he moves his wedge sides to different positions around the loop, because he is changing the size of the surface.  It doesn't mean the EMF is "in the wires".

I think this confusion happens because of the lumped model we use for induced EMF in inductors and transformers.  You have to stick a voltage source that represents the EMF somewhere in series with the wires.  You can stick it anywhere that makes sense.  We get so used to this model that we think that the EMF is "in the wires" of the inductor or "in the turns" of the transformer.  In fact it is just a model to give us the right voltage at the terminals of the transformer, and is not an actual voltage source in series with the wires in a specific location.

That being said, I think his video is a nice demonstration of Faraday's law and this particular setup.  It shows the effect of different measurement path choices and explains things fairly clearly.
« Last Edit: November 24, 2018, 11:48:10 pm by rfeecs »
 
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Offline bsfeechannel

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Re: Does Kirchhoff's Law Hold? Disagreeing with a Master
« Reply #249 on: November 24, 2018, 11:45:11 pm »
but Mehdi's not responsible for other "people" transforming the discussion into any "libel".

Thank you for admitting that people are really turning the discussion into a libel against Lewin instead of realizing the limitations of Kirchhoff or being encouraged to learn Maxwell.

Admitting the problem is the first step to the solution.
 
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