#562 – Electroboom!

[jesuscf]

What non-conservative electric field are you talking about?

So, what is generating the external electric field?  Is the circuit under test between the plates of a giant capacitor with a varying voltage applied to it?  I thought that in Lewin's experiment we had an varying external magnetic field generated by a coil.  That is why I am asking.

[Jesse Gordon]

Really, this feels like discussing with a flatearther.

Please don't say that. Don't think for a moment that the feeling isn't mutual.
...

With both sides feeling like they are debating flat earthers.

And the rest not having a clue what is really being discussed.

In short it is like this.
Lewin: KVL doesn't hold for circuits immersed in a non-conservative electric field, here is the theory to support this claim and here is the demonstration.
McDonald: Your calculations and your experiment are spot-on, Lewin, but don't say KVL doesn't hold because, although it really doesn't describe your circuit very well, I can still use KVL equations to arrive at the same results. Here is the calculations. It is a math trick used to solve various problems in electromagnetism.
Lewin: Yeah. I know many authors use that trick and even call the attention to the fact that you will not find the EMF as a voltage in the circuit, but people don't pay attention to that and try to invent all kinds of unscientific explanations to prove that there is a voltage there hidden, or somehow masked, in the circuit.
McDonald: I agree, this can be misleading sometimes.
Mehdi (intruding on adults' conversation): Hey Lewin, I think you're wrong and I have McDonald's paper to prove it. Your experiment is flawed.
Lewin: Talk to Belcher. I'm retired.
Mehdi: Belcher, please, say I'm right, say I'm right, please, please, please. I'm in desperate need of viewership and I need to convey the idea that I'm an expert electromagnetism.
Belcher: Alright, Mehdi. You're right, BUT, and that's a big BUT, only when it comes to circuits with lumped components and no varying magnetic fields inside the path of the circuit.
Mehdi Woohoo! You see audience? I'm right. Who said that? An MIT professor and the paper by McDonald. Lewin is wrong. Now subscribe, hit the like bottom, pour your sweat money into my Patreon account and buy the sponsor's shit.

People do exactly that and prove how humans failed as a species.

Or maybe it's like this:

Lewin: Hello, hello, hello! Today I am going to show you something amazing! Something so amazing that you will be telling your grandchildren about it!
Lewin: In fact, it is so amazing that this is probably the only time in your entire life that you will see it!

He then presents an air core transformer, which he has incorrectly drawn on the chalkboard, and declares:

Lewin: KVL IS FOR THE BIRDS! All the textbooks are wrong! Only I am the source of truth on this matter, and even my fellow professors think I CHEATED! That shows you what THEY do!! They must be all cheaters! Yes, the whole world is insane but me!

Mehdi shocks himself a few times to see if this newfound knowledge will sink in and make sense. But it doesn't, so like any seeker of truth worth his sparks, he shocks himself a few more times and maybe melts down some clip leads, and then gets busy doing experiments, and finds that Lewin was incorrectly probing.

Mehdi: Professor Lewin, good sir, I tried my best to understand this, but I think you're not probing correctly. What am I missing?

Lewin: FLAT EARTHER! FLAT EARTHER! I do not argue with flat earthers! I won't even watch your video, but you're just wrong! KVL IS FOR THE BIRDS!

Mehdi: Professor McDonald, Professor Belcher, I'm really trying my best to understand this, and my fingers hurt and it smells like burnt clip leads in here. It looks to me like when correctly probing, KVL holds fine. It looks like Professor Lewin did not account for the dB/dt in the loop formed by his volt meter leads, which he did not depict as being magnetically coupled to his loop under test. But he won't even watch my video. What am I missing here?

McDonald: Yeah, he probably can't stand to see you shocking yourself and burning up perfectly good clip leads.
McDonald: Also, Dr. Lewin is as much of a showman as you. He uses diversion and an obsolete version of a "law" to create an apparent paradox.
McDonald: But you are right, Lewin’s circuit is within the range of applicability of Kirchhoff’s loop equations, which
can be used to predict measurements by the “voltmeters” in the experiment.

Belcher: Lewin has fallen for a very common misconception where he thinks that the -L(dI/dt) voltage read by volt meters represents -∫E.dl through the inductor, but that's false. Feynman is very clear that while -∫E.dl through a superconductor is zero, the voltage difference across the inductor is defined as ∮E.dl  (which he says is EMF) -- and this is Faradays law -L(dI/dt).
Belcher: According to Feynman's definition, the sum of all the voltage differences around the circuit is zero (that is, KVL holds) +V - IR - Q/C - L(dI/dt)=0, but the first three terms here are the -∫E.dl through various circuit elements, and the last term has NOTHING to do with the -L(dI/dt) through the inductor, which is the part that Lewin is all hung up on about being zero. The -∫E.dl term is zero, but it's not the only term: The remaining term, -L(dI/dt), is not zero, and he's ignoring that.
Belcher:  In that sense, you correctly argue that KVL holds. Just keep in mind that because the inductor is so different from the other elements, it is defined differently. But it's still a unit of volts, it's still a real measurable -- and lumpable voltage for the sake of KVL.

Mehdi shocks himself and burns up some more wires.





Also, Hey, did you see my request to you here? https://www.eevblog.com/forum/amphour/562-electroboom!/msg3820280/#msg3820280

Edit: Fixed the link.

[jesuscf]

McDonald: ... He uses diversion and an obsolete version of a "law" to create an apparent paradox.

That is the root of the controversy.  Everything else is noise.

Lewin thinks that this is the definition of KVL:

\$\oint_{}^{}E.dL=0\$

While this is the accepted definition of KVL (since at least 1909, the earliest reference I found, but must likely older than that):

\$emf=\oint_{}^{}E.dL=-\frac{d }{dt}\int_{S}^{}B.dS\$

And before the usual blockheads start arguing with me, read the 5 pages I took from "Engineering Electromagnetics" by Hayt and Buck (8th edition) where you can find a better explanation of what I wrote above.  In one of the paragraphs, the authors even point out the need for an updated definition of KVL (despite Lewin saying than nobody does it, and it is crime against humanity or something dramatic along those lines):

"Equation (20) is true for static fields, but we will see in Chapter 9 that Faraday demonstrated it was incomplete when time-varying magnetic fields were present. One of Maxwell’s greatest contributions to electromagnetic theory was in showing that a time-varying electric field produces a magnetic field, and therefore we should expect to find later that Eq. (20) is not correct when either E or the magnetic field varies with time."

.
.
.

"Equation (20) 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 (20) must be amended before we can apply it to time-varying fields."

It is the amended equation (the one that includes Faraday law) that nowadays is known as KVL.

[Sredni]

Mehdi talked about a LUMPED circuit in his first video, he applied (extended) KVL to it and said "KVL holds".

So if the one circuit which Lewin and Mehdi agreed about was not even an argument, then why the tarzan did Belcher say "As ARGUED by Mehdi?"

Here, read and learn your own language:

https://www.thefreedictionary.com/argue

Look at the usage examples and don't stop to celebrate once you find your confirmation bias.

So you're saying that Mehdi argued that KVL holds for a bunch of circuits including lumpable and unlumpable, and Belcher only agreed with the argument for Mehdi's lumpable circuit?
(but neglected to say that he disagreed with any of the rest..)

That sentence written by Belcher is explicitly referencing the RLC lumped circuit. It comes after a sentence that explicitly includes the equation of that lumped RLC circuit. And it is closed by a subordinate that explicitly references the other three elements of that lumped RLC circuit.
My take is that Belcher was talking arguing about that lumped RLC circuit.

But in the universe where Spock has grown a goatee... who knows?

[Sredni]

updated

About lumped and not lumped

[Sredni]

McDonald: ... He uses diversion and an obsolete version of a "law" to create an apparent paradox.

That is the root of the controversy.  Everything else is noise.

Lewin thinks that this is the definition of KVL:

\$\oint_{}^{}E.dL=0\$

While this is the accepted definition of KVL (since at least 1909, the earliest reference I found, but must likely older than that):

\$emf=\oint_{}^{}E.dL=-\frac{d }{dt}\int_{S}^{}B.dS\$

And before the usual blockheads start arguing with me, read the 5 pages I took from "Engineering Electromagnetics" by Hayt and Buck (8th edition)

You call others 'blockheads' but after 13 pages in this thread, and nearly forty in the previous one you have not yet understood that Hayt is talking about the 'amended KVL' that can be applied to circuits with inductors and that is not disputed here (if not for the semantics 5 + 3 + 0 = 8 vs 5 + 3 - 8 = 0 ).
Do you really think you are the only one to have read Hayt?

[bdunham7]

So, what is generating the external electric field?  Is the circuit under test between the plates of a giant capacitor with a varying voltage applied to it?  I thought that in Lewin's experiment we had an varying external magnetic field generated by a coil.  That is why I am asking.

There is a long core with a varying magnetic flux at the center of the ring.  The magnetic field is only varying within the core.  I had pointed out that the return flux of the solenoid would generate a varying magnetic field as well, but apparently that has been shown both mathematically and experimentally to be very low.  I haven't seen or measured the apparatus myself, so I'll assume that is correct--even if there were such a contribution, it would be a lot lower than the contribution directly from the core.  So the circuit itself is not 'immersed' in a varying magnetic field of any significance.

This varying flux creates a rotational electric field concentrically around it.  This rotational field is said to have 'curl', and that makes it non-conservative, which essentially means that you can lose or gain energy when you go in a circle and come back to the same spot.  In a field with no curl, coming back to the same spot will always result in no net work--that is conservative.

Given your previous comments I would have assumed you already knew all that, so that's why I'm wondering why you are asking.  Have I misunderstood?

[jesuscf]

McDonald: ... He uses diversion and an obsolete version of a "law" to create an apparent paradox.

That is the root of the controversy.  Everything else is noise.

Lewin thinks that this is the definition of KVL:

\$\oint_{}^{}E.dL=0\$

While this is the accepted definition of KVL (since at least 1909, the earliest reference I found, but must likely older than that):

\$emf=\oint_{}^{}E.dL=-\frac{d }{dt}\int_{S}^{}B.dS\$

And before the usual blockheads start arguing with me, read the 5 pages I took from "Engineering Electromagnetics" by Hayt and Buck (8th edition)

You call others 'blockheads' but after 13 pages in this thread, and nearly forty in the previous one you have not yet understood that Hayt is talking about the 'amended KVL' that can be applied to circuits with inductors and that is not disputed here (if not for the semantics 5 + 3 + 0 = 8 vs 5 + 3 - 8 = 0 ).
Do you really think you are the only one to have read Hayt?

Really? So you are admitting that the very first post in this thread is incorrect?  Here it is for reference:

Dave, KVL doesn't hold under a varying magnetic field.

[Sredni]

You call others 'blockheads' but after 13 pages in this thread, and nearly forty in the previous one you have not yet understood that Hayt is talking about the 'amended KVL' that can be applied to circuits with inductors and that is not disputed here (if not for the semantics 5 + 3 + 0 = 8 vs 5 + 3 - 8 = 0 ).
Do you really think you are the only one to have read Hayt?

Really? So you are admitting that the very first post in this thread is incorrect?  Here it is for reference:

Dave, KVL doesn't hold under a varying magnetic field.

Inside your circuit path. Or inside any loop (such as a measurement loop) you wanna apply the voltage loop rule to.
But if you can hide the flux inside an inductor and skip it, by considering your circuit path jumping at the terminals, then you end up with a circuit path that is flux free. There you can apply 'modified', 'extended', 'new', 'upgraded', 'enhanced' KVL by treating the surface integral on the rhs AS IF it were a path integral on the left. So, you go from 5 + 3 + 0 = 8 to 5 + 3 - 8 = 0 . And you can feel like you're in high school again.

But for circuits where it is not possible to 'hide' the flux inside a 'detached' component, like Lewins ring WHOSE CIRCUIT PATH IS REQUIRED TO RUN AROUND THE CHANGING FLUX - IT IS A GEOMETRIC CONSTRAINT IMPOSED BY DESIGN - you can no longer pull the 'extended KVL' trick. You have to fold back to Faraday.

[EEVblog]

Who was it again in the original KVL forum thread that deleted all their (excellent) contributions?

[jesuscf]

You call others 'blockheads' but after 13 pages in this thread, and nearly forty in the previous one you have not yet understood that Hayt is talking about the 'amended KVL' that can be applied to circuits with inductors and that is not disputed here (if not for the semantics 5 + 3 + 0 = 8 vs 5 + 3 - 8 = 0 ).
Do you really think you are the only one to have read Hayt?

Really? So you are admitting that the very first post in this thread is incorrect?  Here it is for reference:

Dave, KVL doesn't hold under a varying magnetic field.

Inside your circuit path. Or inside any loop (such as a measurement loop) you wanna apply the voltage loop rule to.
But if you can hide the flux inside an inductor and skip it, by considering your circuit path jumping at the terminals, then you end up with a circuit path that is flux free. There you can apply 'modified', 'extended', 'new', 'upgraded', 'enhanced' KVL by treating the surface integral on the rhs AS IF it were a path integral on the left. So, you go from 5 + 3 + 0 = 8 to 5 + 3 - 8 = 0 . And you can feel like you're in high school again.

But for circuits where it is not possible to 'hide' the flux inside a 'detached' component, like Lewins ring WHOSE CIRCUIT PATH IS REQUIRED TO RUN AROUND THE CHANGING FLUX - IT IS A GEOMETRIC CONSTRAINT IMPOSED BY DESIGN - you can no longer pull the 'extended KVL' trick. You have to fold back to Faraday.

Yes, we can use KVL (the current version, not the one from the mid 1800) if you account for every contributing induced voltage and every voltage drop.   In the attached figure, Lewin is claiming to measure voltage Vxy from the left with 'voltmeter' V1 and to measure voltage Vxy from the right  with 'voltmeter' V2.  He is amazed that the measurements are different, then he concludes that KVL doesn't work!  But in reality what he is measuring is voltage Vkm with 'voltmeter' V1 and voltage Vhj with 'voltmeter' V2.  He didn't add the induced voltages Va, Vb, Vc, and Vd to the circuit diagram as if they didn't exist.

[Sredni]

Who was it again in the original KVL forum thread that deleted all their (excellent) contributions?

The problem is that jesuscf had read them before I deleted them. Those contribution did not do any good to him, it appears (well, back then IIRC he was arguing that Lewin's ring was a transmission line). And anyway I collected them in my answers on Stack Exchange. Do you think he read them?
Anyway, I explained why I did what I did back then. There is no greater sin in my eyes than destroying something I put my time into, for free (even if it was collateral damage). Criticize all you want, no problem. Call me names, it's fun for me either. But if my efforts are done for nothing... The ferret giveth, the ferret taketh.

Anyway, I am not going to delete any of my last posts. I made an exception because it is a shame to see so many people misguided and the one person who tried to show them the beauty of EM vilified (Lewin), but also because I am literally intrigued by the the phenomena (self-bias, exclusion of critical voices, and mostly the general gaslighting that social media are perfecting in the last years - thumbs down, anyone? ).

I wonder if Mehdi (and I put Belcher into this as well, for not being more explicit) realize the damage he has done and is doing (not about Lewin, but the misconceptions that get amplified and propagated). McDonald, on the other hand has just put forward a legitimate approach (whose exposition I personally don't like, but that's just a matter of personal tastes), but maybe he could have avoided acting surprised of the 'paradox', considering the history of misunderstanding behind it. He practically ended up being the one spare climatologist that published a paper against climate change.

[jesuscf]

Who was it again in the original KVL forum thread that deleted all their (excellent) contributions?

The problem is that jesuscf had read them before I deleted them. Those contribution did not do any good to him, it appears (well, back then IIRC he was arguing that Lewin's ring was a transmission line).

I said what???  My posts are still there; I didn't erase them, so please let me know were I said that...  If I remember correctly I said that a long, long wire can be modeled as a transmission line.  Transmission lines are often modeled as lumped pi circuits.  I even pointed out that Hayt explicitly used KVL to develop such model.

[thinkfat]

Also, Hey, did you see my request to you here? https://www.eevblog.com/forum/amphour/562-electroboom!/msg3820280/#msg3820280

Yes, I saw it. I'll give it a shot.

Since you've formulated an ideal transformer, the easiest way to calculate the result is to lump the resistance of the wires and use "reflection" to transform all resistors and voltage sources over to the secondary side. The result is attached.

I'd like to add, though, that this has nothing to do with what we're discussing here. This "assignment" is so remote from Physics that you need to know nothing about Faraday or Maxwell, just some basic rules of circuit theory. But that's what engineers are being taught today in their first or maybe second year: how to work with equivalences so that you don't need to get into the nitty gritty of the REAL WORLD you're demanding to model in every other post.

[Jesse Gordon]

McDonald: ... He uses diversion and an obsolete version of a "law" to create an apparent paradox.

That is the root of the controversy.  Everything else is noise.

Lewin thinks that this is the definition of KVL:

\$\oint_{}^{}E.dL=0\$

While this is the accepted definition of KVL (since at least 1909, the earliest reference I found, but must likely older than that):

\$emf=\oint_{}^{}E.dL=-\frac{d }{dt}\int_{S}^{}B.dS\$

Wait. You mean the Lewies on youtube have been badgering me for a year because Lewin was using a 110+ year outdated definition? 

*Gasp* Why couldn't they just tell me it was a definition game the whole time?

I guess that explains why they are so reluctant to actually answer practical real life type transformer questions.

And before the usual blockheads start arguing with me, read ....

The way they don't answer my questions, I thought they couldn't read!

So far most of them won't respond to my challenge
(Kudos to Thinkfat who did respond after a while!)

I want to know if they actually know this stuff better than me, so I made a problem for them to solve, so far silence on that topic from most of them.

[Jesse Gordon]

Also, Hey, did you see my request to you here? https://www.eevblog.com/forum/amphour/562-electroboom!/msg3820280/#msg3820280

Yes, I saw it. I'll give it a shot.

Since you've formulated an ideal transformer, the easiest way to calculate the result is to lump the resistance of the wires and use "reflection" to transform all resistors and voltage sources over to the secondary side. The result is attached.

I'd like to add, though, that this has nothing to do with what we're discussing here. This "assignment" is so remote from Physics that you need to know nothing about Faraday or Maxwell, just some basic rules of circuit theory. But that's what engineers are being taught today in their first or maybe second year: how to work with equivalences so that you don't need to get into the nitty gritty of the REAL WORLD you're demanding to model in every other post.

Thank you!

It does have to do with some of what we're talking about - it is related to the experiment with the copper loop secondary winding we did the other day.

But the point is to give you three an opportunity to demonstrate that you do know something about the topic.

Now let's see if the other two fellas come up with the same answer as you. As I said, once all three have shared their answer, I'll share mine. If they don't do so in a couple days, I'll just assume they don't know how to do it and share mine anyway.

[thinkfat]

Thank you!

It does have to do with some of what we're talking about - it is related to the experiment with the copper loop secondary winding we did the other day.

But the point is to give you three an opportunity to demonstrate that you do know something about the topic.

Now let's see if the other two fellas come up with the same answer as you. As I said, once all three have shared their answer, I'll share mine. If they don't do so in a couple days, I'll just assume they don't know how to do it and share mine anyway.

It has some resemblance to the copper loop experiment. But it is already so heavily simplified and distorted that it's useless to argue about what you actually measured and how.
I also think that what you'd learn from anyone being able to solve this "challenge" or not has anything to do with their understanding of Faradays Law, because, well, it's not relevant.

Anyway, my turn now:

See the attached arrangement. If it looks familiar, this is your EI-core setup, just with a toroidal core instead.

What voltages would you measure across the resistors? What voltages would you measure across the wires? Show the arrangement of your probe wires.

The actual value of R is not relevant, assume it is large enough to make the resistance of the wiring negligible. Assume the magnetic flux in the core corresponds to a value of "1V" induced in the secondary.
Also assume the length of the wires between the resistors is identical, so that it looks nice and symmetric (hint: it doesn't actually matter, I'm just a sucker for symmetric arrangements).

[bsfeechannel]

Or maybe it's like this:

Lewin: Hello, hello, hello! Today I am going to show you something amazing! Something so amazing that you will be telling your grandchildren about it!
Lewin: In fact, it is so amazing that this is probably the only time in your entire life that you will see it!

He then presents an air core transformer, which he has incorrectly drawn on the chalkboard, and declares:

Lewin: KVL IS FOR THE BIRDS! All the textbooks are wrong! Only I am the source of truth on this matter, and even my fellow professors think I CHEATED! That shows you what THEY do!! They must be all cheaters! Yes, the whole world is insane but me!

Mehdi shocks himself a few times to see if this newfound knowledge will sink in and make sense. But it doesn't, so like any seeker of truth worth his sparks, he shocks himself a few more times and maybe melts down some clip leads, and then gets busy doing experiments, and finds that Lewin was incorrectly probing.

Mehdi: Professor Lewin, good sir, I tried my best to understand this, but I think you're not probing correctly. What am I missing?

Lewin: FLAT EARTHER! FLAT EARTHER! I do not argue with flat earthers! I won't even watch your video, but you're just wrong! KVL IS FOR THE BIRDS!

Mehdi: Professor McDonald, Professor Belcher, I'm really trying my best to understand this, and my fingers hurt and it smells like burnt clip leads in here. It looks to me like when correctly probing, KVL holds fine. It looks like Professor Lewin did not account for the dB/dt in the loop formed by his volt meter leads, which he did not depict as being magnetically coupled to his loop under test. But he won't even watch my video. What am I missing here?

McDonald: Yeah, he probably can't stand to see you shocking yourself and burning up perfectly good clip leads.
McDonald: Also, Dr. Lewin is as much of a showman as you. He uses diversion and an obsolete version of a "law" to create an apparent paradox.
McDonald: But you are right, Lewin’s circuit is within the range of applicability of Kirchhoff’s loop equations, which
can be used to predict measurements by the “voltmeters” in the experiment.

Belcher: Lewin has fallen for a very common misconception where he thinks that the -L(dI/dt) voltage read by volt meters represents -∫E.dl through the inductor, but that's false. Feynman is very clear that while -∫E.dl through a superconductor is zero, the voltage difference across the inductor is defined as ∮E.dl  (which he says is EMF) -- and this is Faradays law -L(dI/dt).
Belcher: According to Feynman's definition, the sum of all the voltage differences around the circuit is zero (that is, KVL holds) +V - IR - Q/C - L(dI/dt)=0, but the first three terms here are the -∫E.dl through various circuit elements, and the last term has NOTHING to do with the -L(dI/dt) through the inductor, which is the part that Lewin is all hung up on about being zero. The -∫E.dl term is zero, but it's not the only term: The remaining term, -L(dI/dt), is not zero, and he's ignoring that.
Belcher:  In that sense, you correctly argue that KVL holds. Just keep in mind that because the inductor is so different from the other elements, it is defined differently. But it's still a unit of volts, it's still a real measurable -- and lumpable voltage for the sake of KVL.

Mehdi shocks himself and burns up some more wires.

I’d say you’d make an excellent Hollywood script  writer, if we didn’t know who invented all the myth above for the sole aim of boosting his own viewership, at the expense of truth. But we’re not buying it because serious science and engineering.

As you keep forwarding this misinformation, you’ll not advance a single bit in the understanding of the electromagnetic phenomenon, exactly as Mehdi declares every time, including in this very interview.

Also, Hey, did you see my request to you here? https://www.eevblog.com/forum/amphour/562-electroboom!/msg3820280/#msg3820280

Your question is not aimed at honestly trying to understand the issue. If it were, you would have already heeded what we’ve written all along this thread.

[Jesse Gordon]

About lumped and not lumped

For the other forum fellows who have not yet deciphered your view: Jesse here, wants to treat the two red straight segment of wire in his setup as two distinct lumped transformers.

Are you saying that the two red wires passing through the two halves of my transformer core are not lumpable voltage sources?

Well, it is kinda lumpable, and if you can attach it to a circuit that can be shrunk (lumped) to a point (this requires that there be no flux caught inside), you can consider it a lumped component in a lumped circuit.
Problem is, you cannot have a spatially extended component along your lumped circuit path, so you at least need to have the terminals close together, ideally separated by an infinitesimal distance.
In this picture I used the terms lumpable, kinda lumpable and unlumpable


lumpable kindalumpable unlumpable

But maybe it would be preferable to use: lumped, lumpable, and unlumpable. ( It's always after you have scanned them that you notice these things...)

In order to make that lumpable system of yours

Pic torus with straight wire and circuit missing a coil
link [url]https://i.postimg.cc/gjhfcHXZ/screenshot-10.png[/url]

into a lumped transformer you just have to solve the problem of how to put those terminals close together. How do you plan to do it? There are two options

Option 1: You modify your component to fit the circuit
Take one on the other side to almost meet the other, or nearly join them together halfway. Now you can actually see a voltage in the space between terminals.


Pic bent wire around torus: change the component to fit the circuit
link [url]https://i.postimg.cc/g2mfdRYx/screenshot-11.png[/url]

And if you stay outside your black box and you do not run around the flux it will be always the same. Notiche how the charges have moved from the conductor's extreme to the resistor.

Option 2: You modify your circuit to fit the component
You insist in calling that piece of wire a transformer? Well, suit yourself, I will not alter it at all. But I still need to put it into the circuit, so I make connections to its end terminals


Pic change the circuit to fit the component
link [url]https://i.postimg.cc/7LLdJkJD/screenshot-12.png[/url]

and now you have your component unaltered attached to your circuit. The circuit path (highlighted here by the dotted line) is now including the component and along with it, the flux lines. And since your circuit path encompasses a variable magnetic flux, the circulation of the electric field can no longer be zero. This means that the path integral of the electric circuit depends on the path and therefore, voltage is path dependent. Kirchhoff's loop law is for the birds.

There is also the 'wishful thinking' option:
You just ignore component and circuit boundaries and cram everything together, hoping for the best. Let's apply this to your circuit inside the EI transformer.
Here on the left is the circuit with an elastic mebrane on it. It is integer and pristine. Look how happy it is, singing one of Madonna's earliest greatest hits.
But then you put it inside the EI transformer. Do you really think you can do that without breaking the membrane? Look what you did to your little circuit's membrane:


fig rammed to death
link [url]https://i.postimg.cc/65LmH3dt/screenshot-13.png[/url]

I really hope you had proof of previous consent, because you broke the law: Kirchhoff's law, to be specific.


Just look at the circuit path.
link [url]https://i.postimg.cc/xd7xkbSy/screenshot-17.png[/url]

The broken membrane is proof that your circuit cut the flux lines. KVL is for the birds. Also, since your circuit path is going around the changing flux with no way to exclude it, your circuit is unlumpable. Lewin would be proud of you.


Bonus Track: What's the deal with the straight partial 'turn'?
I believe I figured you out now.
You are a lumper who believes that when a piece of wire 'goes through the hole' in the transformer, it develops a voltage, that is nonzero, irregardless of the path it is computed on! As if the hole was some kind of portal to another dimension, like a stargate.
No. If it intercepts the induced electric field, the wire gets polarized, and you might see charges of opposite sign at the extremities, but the voltage between point A at one end and point B at the other end is not unique: it depends on the path.

Along all these paths, the voltage (i.e. the work done per unit charge that is compute as minus path integral of E.dl) is zero (just like with a polarized conductor in an electrostatic field - see my previous silent post)


Fig straight wire and paths zero v
link  [url]https://i.postimg.cc/mZ7XDDpC/screenshot-14.png[/url]

Along this other type of paths, paths that together with the piece of wire form a loop that runs around the changing flux, the voltage is nonzero ( one turn emf, so to speak). There is your transformer.


Fig straight wire and paths emf
link [url]https://i.postimg.cc/HL70hZfX/screenshot-15.png[/url]

But how can you make it lumped / part of a lumped circuit? Bend the conductor a little more so as to bring the terminals almost together, as shown above. Now you can insert it into a shrinkable circuit and, if the circuit path does not include variable flux you have a lumped circuit where KVL holds. You will see a jump in voltage at the component's terminals. The displaced charge is not there, though, it is at the resistor's boundaries if there is one, or facing the gap if it is open circuited.

Which side is the hole in the core?
Incidentally, this is the equivalent of what you want to consider a lumped transformer with the toroidal or EI cores,  but with the core in the form of an infinitely long cylinder where the primary is an infinitely long solenoid. So, you have a piece of wire, and the 'hole' is basically the whole space. Where is left of the hole, or the right of the hole? Is the wire inside the core, or outside of it?


Pic straight wire solenoid
link [url]https://i.postimg.cc/qvWyyczR/screenshot-16.png[/url]

Do you still see a lumped transformer? Or in order to call that piece of polarized wire a transformer you first need to bend it and bring the terminals together in a way that the wire almost encircles the core?

First of all, let me say THANK YOU for drawing all those very nice diagrams, and laying out your post so nicely.
I really honestly am genuinely grateful.

I do have one question though, regarding:

But how can you make it lumped / part of a lumped circuit? Bend the conductor a little more so as to bring the terminals almost together, as shown above. Now you can insert it into a shrinkable circuit and, if the circuit path does not include variable flux you have a lumped circuit where KVL holds. You will see a jump in voltage at the component's terminals. The displaced charge is not there, though, it is at the resistor's boundaries if there is one, or facing the gap if it is open circuited.

(Bold mine.)

Do I understand correctly that the voltage across the resistor (and consequently the heat produced by the resistor) will change when I go from Option 1 configuration and Option 2 configuration?

For the sake of discussion, let's say I took a 5ft length of wire, passed it through the core once and formed a large round loop with it and my volt meter, and wrote that voltage down.
Then let's say I took that same wire and hugged the core tightly and twisted it all the way to the volt meter so it was a twisted pair from the core to the volt meter, and measured the volts:

Here's what I mean:



Would the two measurements be different? or the same?

If V1 is different than V2, what is the general magnitude and sign of the difference? Are we talking like a few percent? or a part per million?

(The core is small, about 3 inches in it's longest dimension.)

In metric, the core's maximum dimension is roughly 8cm and the length of the wire is about 150cm.

So it's not like I have a HUGE core in mind.

Thank you very much!

[Sredni]

Also, Hey, did you see my request to you here? https://www.eevblog.com/forum/amphour/562-electroboom!/msg3820280/#msg3820280

Yes, I saw it. I'll give it a shot.

Please, don't. He's just trying to pollute the thread.
He probably pulled out an old high school problem he had solved, and now wants us to waste out time on it to prove what?
As if one could not google how to computed inductances values, or how to model a transformer with lumped parameters? I did this kind of exercises when I was seventeen, and I hated them. Especially the vector diagrams, they are so ugly and lack any kind of beauty.
Besides having nothing to do with the unlumpable Lewin's ring, his problem is not even interesting because he doesn't even model the hysterisis. And with all the simplification assumptions one has to make to get to a lumped model, he wants what? Ten significative digits?

Please, move the problem in the beginner section of the forum, if you want to solve it. Here it will only dilute the thread.

Edit: I had one sentence unfinished

[thinkfat]

Yes, I saw it. I'll give it a shot.

Please, don't. He's just trying to pollute the thread.
He probably pulled out an old high school problem he had solved, and now wants us to waste out time on it to prove what?
As if one could not google how to computed inductances values, or how to model a transformer with lumped parameters? I did t
Besides having nothing to do with the unlumpable Lewin's ring, his problem is not even interesting because he doesn't even model the hysterisis. And with all the simplification assumptions one has to make to get to a lumped model, he wants what? Ten significative digits?

Please, move the problem in the beginner section of the forum, if you want to solve it. Here it will only dilute the thread.

Why? Problem and solution nicely demonstrate his level of expertise. That can't hurt.
Besides, the solution (trivial, 3-resistor circuit plus voltage source) and all two lines of Ohms law are already attached to my post for anyone wanting to calculate the result to 10 digits. I don't feel like wasting space for this in the beginner section.

[Sredni]

About lumped and not lumped
For the other forum fellows who have not yet deciphered your view: Jesse here, wants to treat the two red straight segment of wire in his setup as two distinct lumped transformers.

Are you saying that the two red wires passing through the two halves of my transformer core are not lumpable voltage sources?

I see you are capable of quoting and entire post. Good. How about (re-)reading it, now? Because to answer this question I should rewrite it as it is.

Do I understand correctly that the voltage across the resistor (and consequently the heat produced by the resistor) will change when I go from Option 1 configuration and Option 2 configuration?

Of course you don't understand correctly.
Here is the sentence you highlighted. I will toss in the next sentence too because it's black friday month.

"You will see a jump in voltage at the component's terminals. The displaced charge is not there, though, it is at the resistor's boundaries if there is one, or facing the gap if it is open circuited."

Now, what makes you think that the component is the resistor? Especially when the sentence immediately after says "The displaced charge is not there, though, it is at the resistor's boundaries if there is one, or facing the gap if it is open circuited."

If "NOT THERE" means "AT THE RESISTOR'S", how can "there" mean "at the resistor's"?

[Sredni]

Yes, I saw it. I'll give it a shot.

Please, don't. He's just trying to pollute the thread.

Please, move the problem in the beginner section of the forum, if you want to solve it. Here it will only dilute the thread.

Why? Problem and solution nicely demonstrate his level of expertise. That can't hurt.

Because it will uselessly waste space here.

Besides, the solution (trivial, 3-resistor circuit plus voltage source)

You need to model more than that. If you find it, have a look at K. C. A. Smith & R. E. Alley "Electrical Circuits, an introduction", chapter 4, section 9 "Single-phase power transformers". It has the simplest treatment of 'real' transformers I have ever seen.

He will drag you down in a series of dozens of post, arguing about any simplificative assumption he did not make in his high-school exercise, and defending any simplification he made, no matter how unrealistic that may be (like--- this looks like a welder's transformer and he's not considering saturation?). It will go on forever.

Remember, I have a crystal ball that almost never fails me.

Edit: grammar! and a little addition.

[thinkfat]

You need to model more than that.

Nah, not really. Look at the constraints given (ideal core, infinite permeability, perfect coupling) and imagine what that does to the standard "non-ideal transformer" model. So much for "dealing with the real world".

[Jesse Gordon]

Or maybe it's like this:

Lewin: Hello, hello, hello! Today I am going to show you something amazing! Something so amazing that you will be telling your grandchildren about it!
Lewin: In fact, it is so amazing that this is probably the only time in your entire life that you will see it!

He then presents an air core transformer, which he has incorrectly drawn on the chalkboard, and declares:

Lewin: KVL IS FOR THE BIRDS! All the textbooks are wrong! Only I am the source of truth on this matter, and even my fellow professors think I CHEATED! That shows you what THEY do!! They must be all cheaters! Yes, the whole world is insane but me!

Mehdi shocks himself a few times to see if this newfound knowledge will sink in and make sense. But it doesn't, so like any seeker of truth worth his sparks, he shocks himself a few more times and maybe melts down some clip leads, and then gets busy doing experiments, and finds that Lewin was incorrectly probing.

Mehdi: Professor Lewin, good sir, I tried my best to understand this, but I think you're not probing correctly. What am I missing?

Lewin: FLAT EARTHER! FLAT EARTHER! I do not argue with flat earthers! I won't even watch your video, but you're just wrong! KVL IS FOR THE BIRDS!

Mehdi: Professor McDonald, Professor Belcher, I'm really trying my best to understand this, and my fingers hurt and it smells like burnt clip leads in here. It looks to me like when correctly probing, KVL holds fine. It looks like Professor Lewin did not account for the dB/dt in the loop formed by his volt meter leads, which he did not depict as being magnetically coupled to his loop under test. But he won't even watch my video. What am I missing here?

McDonald: Yeah, he probably can't stand to see you shocking yourself and burning up perfectly good clip leads.
McDonald: Also, Dr. Lewin is as much of a showman as you. He uses diversion and an obsolete version of a "law" to create an apparent paradox.
McDonald: But you are right, Lewin’s circuit is within the range of applicability of Kirchhoff’s loop equations, which
can be used to predict measurements by the “voltmeters” in the experiment.

Belcher: Lewin has fallen for a very common misconception where he thinks that the -L(dI/dt) voltage read by volt meters represents -∫E.dl through the inductor, but that's false. Feynman is very clear that while -∫E.dl through a superconductor is zero, the voltage difference across the inductor is defined as ∮E.dl  (which he says is EMF) -- and this is Faradays law -L(dI/dt).
Belcher: According to Feynman's definition, the sum of all the voltage differences around the circuit is zero (that is, KVL holds) +V - IR - Q/C - L(dI/dt)=0, but the first three terms here are the -∫E.dl through various circuit elements, and the last term has NOTHING to do with the -L(dI/dt) through the inductor, which is the part that Lewin is all hung up on about being zero. The -∫E.dl term is zero, but it's not the only term: The remaining term, -L(dI/dt), is not zero, and he's ignoring that.
Belcher:  In that sense, you correctly argue that KVL holds. Just keep in mind that because the inductor is so different from the other elements, it is defined differently. But it's still a unit of volts, it's still a real measurable -- and lumpable voltage for the sake of KVL.

Mehdi shocks himself and burns up some more wires.

I’d say you’d make an excellent Hollywood script  writer, if we didn’t know who invented all the myth above for the sole aim of boosting his own viewership, at the expense of truth. But we’re not buying it because serious science and engineering.

As you keep forwarding this misinformation, you’ll not advance a single bit in the understanding of the electromagnetic phenomenon, exactly as Mehdi declares every time, including in this very interview.

Also, Hey, did you see my request to you here? https://www.eevblog.com/forum/amphour/562-electroboom!/msg3820280/#msg3820280

Your question is not aimed at honestly trying to understand the issue. If it were, you would have already heeded what we’ve written all along this thread.

Hey, I thought your highly biased skit was pretty good too! Maybe we should make a movie? 

You say that you think I "keep forwarding this misinformation." If you think that's true, then why not try to set me straight in the most effective way of actually answering my questions so I can understand better? You dodge every question you can, and you avoid the rest.

While I have no degrees and I'm certainly not a math wiz, I have a nack for making videos that illustrate my point. As long as I think my point is true, I continue to do so, and then you have to deal with the people who see the videos.

Your best bet for solving that problem is to actually work with me, at my level, to show me exactly where I went wrong -- not pasting large sections of whatnot and then refusing to answer questions when I'm confused by what you're actually saying.

My challenge of the 100v:10v stepdown transformer was aimed at helping me understand who here knows what they are talking about.

Turns out only Thinkfat has a clue, the other two of you couldn't solve it. And that's what I wanted to know.