Sick of ridiculous KVL infighting

[instrumental]

40 pages and a few months on, some nerds don't seem to know when to quit arguing. The video Mehdi made about a "principled disagreement" with Lewin's lectures is rough as well, and now this has spiralled into numerous YouTube videos trying and failing to explain EM theory. I'm surprised to see so much discord in a community of professional electronics engineers.

I'm quite tired of seeing this, so I am hoping to provide a fairly definitive explanation of:

• Why KVL doesn't always work (e.g. why we don't use it for RF circuits or optics),
• Why KVL can be used to analyse low-frequency circuits (power, audio, etc), and finally,
• Where the gap is.

So, here we go.

Voltages measure electrostatic potential; the electric field is the gradient (slope) of the voltage, and the voltage is the potential function of the electric field.

For a potential function to be defined on the field, the field has to be conservative. For a field to be conservative, it has to be path-independent (you can calculate voltage between two points by taking any path through the field; the voltage will only depend on the endpoints). For a field to be path-independent, it has to be curl-free.

Imagine a toy boat circling a drain in the bathtub. We can divide the flow field into divergence-only (flow towards the drain) and curl-only (swirling around the drain) flows. Ignoring the divergence for now, imagine the toy boat is initially stationary. The flow will take the boat with it, and it will begin to pick up speed as work is done by the flow on the boat. Once the boat has made a full revolution of the drain, it is in the same initial place, but it is now in motion; it has acquired energy. This should illustrate to you that a circulating field is not a conservative field; we can't define potential energy between two points because different paths will do different quantities of work.

Now, we might ask, what is the curl of the electric field? This is given by Faraday's law of induction -- it's proportional to the derivative of the magnetic field with respect to time. If we have a changing magnetic field, we have a non-conservative field.

When do we have a changing magnetic field? Well, magnetic fields are made by currents; changing electric fields also create magnetic fields, which gives rise to EM wave propagation. So, any time we have a changing field or current (e.g. AC at any frequency), we can no longer define voltage.

There are two ways out of this. Physicists often work with 4-potentials in EM theory. A vector potential can be defined for the divergence-free field; a scalar potential (voltage) can be defined for the curl-free field, and the two together produce the full field. This magnetic vector potential is significant: the Aharonov-Bohm effect illustrates this nicely. Unfortunately, this doesn't mean we get KVL.

More commonly, approximations can be made which allow the re-introduction of voltages. If dB/dt is sufficiently small that it can be ignored, we can approximate the field as conservative. This is manifestly the case for power lines (50-60Hz) and holds (as a rule of thumb) roughly until the scale of the circuit under consideration is close to one-tenth the wavelength of the signal (e.g. a 1MHz signal has a wavelength in the tens of meters; you don't worry about MHz routing on a small PCB, but you run into RF effects with larger-scale antennae. By 1GHz, you're dealing with centimeters of wavelength and you're squarely in RF territory).

TL;DR field theory explains phenomena from DC, to RF, up to the highest-energy gamma rays, with visible light in between. You wouldn't apply KVL to RF or optics, would you?

[PlainName]

I'm quite tired of seeing this, so I am hoping to provide a fairly definitive explanation of:

Looks to me like you think your explanation is the authoritative explanation and, in order that no-one gets sidetracked by lesser explanations, you've started a new thread just for this. Why couldn't you just put it at the end of the current long thread? Imagine if every participant there started a new thread just to highlight their own authoritative explanation - the entire forum would consist of root posts about this stuff.

If you really want to make it count, delete this thread and just argue the merits in the proper place. Or just sigh and walk off knowing you are right and everyone else can wallow in their mistakes without further bothering you.

[Siwastaja]

you've started a new thread just for this. Why couldn't you just put it at the end of the current long thread?

While I generally agree that creating multiple threads about the same matter is a bad idea - also against forum rules -, in this special case that particular thread moves so fast, driven by what basically is a semiautomated spambot - which is also against forum rules - copypasting same responses and same dummy "questions" weeks and months straight. Any sensible comment gets lost in the noise in a matter of a day, which is probably exactly the reason for such smoke screen.

In reality, the fact is there is no large dispute. The few that run it make it look like large. Their capacity of even generating unique messages is exceeded long ago, which is why jesuscf just basically copypastes.

Quite frankly, it's nothing but playing games and throwing the toys and sand around, by the few remaining (is there more than 2 anymore?) people who can't admit their mistake or shortcomings, like many, including me, could (for me, it sure did take time).

This is why I would like to give a pass to this opening post which, despite being outside of the sandstorm thread, tries to actually be helpful and explain the issue.

Electromagnetism is non-trivial, and for "practical engineers", it can be damn difficult to admit our math is lacking. But I also can't stand intellectual dishonesty.

But really, the game is soon over. The quality of the "opposition" has gone down significantly, from the serious attempts of building usable equivalent circuits in SPICE, that model the experiment, to just rigging physical experiments with careful layout (which never was part of the experiment; this was the eye-opener for me; I can see the difference between circuit layout and good probing), shouting, and thinking that adding more exclamation marks makes KVL hold better.

And why I call it intellectual dishonesty? The answer is simple: because the people who built these Youtube experiments, who constructed the layouts that give "expected" multimeter number on photographs or videos, themselves witnessed the path dependency during tweaking of the layout, to get the error within the expected <2% or so. Think about it.

It sure seems more like flat-earth stuff every day.

[PlainName]

Any sensible comment gets lost in the noise in a matter of a day, which is probably exactly the reason for such smoke screen.

What will prevent this thread also suffering the same fate once it's been discovered?

If someone is disrupting a discussion through foul means then surely the answer is to ask a mod to deal with them. I don't see that giving them more threads to disrupt achieves much. Of course, perhaps the mods will be too busy, fail to see your point or otherwise let things run, but you don't know unless you ask.

But, on the whole, I am not averse per se with skimming the crust off into another smaller and newer thread. It was just the "Listen, my explanation is the right one, so I'm a special case" which poked me.

[nctnico]

you've started a new thread just for this. Why couldn't you just put it at the end of the current long thread?

While I generally agree that creating multiple threads about the same matter is a bad idea - also against forum rules -, in this special case that particular thread moves so fast, driven by what basically is a semiautomated spambot - which is also against forum rules - copypasting same responses and same dummy "questions" weeks and months straight. Any sensible comment gets lost in the noise in a matter of a day, which is probably exactly the reason for such smoke screen.

In reality, the fact is there is no large dispute. The few that run it make it look like large. Their capacity of even generating unique messages is exceeded long ago, which is why jesuscf just basically copypastes.

Quite frankly, it's nothing but playing games and throwing the toys and sand around, by the few remaining (is there more than 2 anymore?) people who can't admit their mistake or shortcomings, like many, including me, could (for me, it sure did take time).

This is why I would like to give a pass to this opening post which, despite being outside of the sandstorm thread, tries to actually be helpful and explain the issue.

Electromagnetism is non-trivial, and for "practical engineers", it can be damn difficult to admit our math is lacking.

Agreed. IMHO the whole point is to understand when a simplification works and when not. Showing electrical phenomena using simple multimeters also raises my eyebrows; I've seen that go wrong too many times.

When skimming through the other thread an interesting question popped into my mind: where does the electricity go that is being fed into an antenna (*). 

* Yes, this is formulated in a very poor way on purpose.

[Siwastaja]

What will prevent this thread also suffering the same fate once it's been discovered?

Nothing, and it will likely happen, after which moderators likely lock up this thread as a duplicate. Just saying I understand why the OP felt like opening a new thread.

If someone is disrupting a discussion through foul means then surely the answer is to ask a mod to deal with them.

Let's face it, that's not realistically going to happen. The discussion is on-topic, actually core of the forum, so this is not a valid excuse to intervene. All that is left is to carefully analyse what's going on, whether the means are foul, and do an informed decision. Moderation on this forum has never worked this way for a simple reason: lack of resources. Moderation is pretty much hit-and-run strategy, and I don't blame Dave & Simon, they have hands full and need to make quick decisions on simple matters (like totally offtopic politics).

So yeah, I pretty much agree with your points.

[Nominal Animal]

40 pages and a few months on, some nerds don't seem to know when to quit arguing.

Ah yes: because they disagree with you, they are nerds.

And you are professional, eh?

No, I don't think so.  I do believe asshat and a coward is a much more appropriate term for the likes of you.

I bet there is also a reason why you created a second account to post this thread –– which, by the way, is against the forum rules.  When your own argument is too weak to gain traction, what better to create an astroturfing account and call the others names and try to make them look ridiculous?

Oh fuck I hate these social games.

[bdunham7]

In reality, the fact is there is no large dispute.

Once I figured that out I tried--rather clumsily I suppose--to point out what I saw as the primary issue leading to the disagreement and later the misdirection of attention as to which 'path' was important--it took me a bit longer than I'd like to admit to catch onto this--that sort of made it look like a much more noteworthy issue than it really is.  But the main contestants weren't interested in any of that, just proving that they were superior and engineers are stupid.  And then along came some additional contestants to confirm that. 

The OP in this thread has a reasonable, short explanation for those that don't want to read 39 pages of name calling and drivel.  However, I would replace

So, any time we have a changing field or current (e.g. AC at any frequency), we can no longer define voltage.

with "there are multiple possible definitions of voltage" or something like that.  Proving that we can't define voltage by measuring something with voltmeters seems a bit silly.

[bdunham7]

No, I don't think so.  I do believe asshat and a coward is a much more appropriate term for the likes of you.

I bet there is also a reason why you created a second account to post this thread –– which, by the way, is against the forum rules.  When your own argument is too weak to gain traction, what better to create an astroturfing account and call the others names and try to make them look ridiculous?

Did I miss something?   

[SiliconWizard]

Proving that we can't define voltage by measuring something with voltmeters seems a bit silly.

Should be obvious... but that's very well put. =)

[Nominal Animal]

Did I miss something?   

Perhaps?  The OP is using a newly created account to call others nerds just because their own opinion is not gaining traction.

(That opinion being "this subject should be clear to everyone, so stop discussing it, it scares me".)

It is a social tactic that happens to push one of my buttons.  I absolutely hate it.

(No, I'm not drunk/high/angry, just very sensitive to these kinds of social-based attacks when someones opinion is not gaining traction.  Others do not care, but I do: I've had enough of them.)

[bdunham7]

Perhaps?  The OP is using a newly created account to call others nerds just because their own opinion is not gaining traction.

I don't know whether the OP is a sockpuppet or a longtime lurker that finally wanted to say something.  I'll presume the latter unless the mods bounce him.

Ordinarily I might agree with you but the thread in question is so vile and polluted I don't think it is even possible to have a sane conversation within it.  I tried to point out a few things that I thought would lead to some agreement, but I regret even wasting the time.

[Nominal Animal]

Ordinarily I might agree with you but the thread in question is so vile and polluted I don't think it is even possible to have a sane conversation within it.  I tried to point out a few things that I thought would lead to some agreement, but I regret even wasting the time.

I avoided that thread for the same reason.  However, starting a new thread with an insult is not a valid way to start a conversation, is it?

(I understand that to some, it is not an insult.  But to me, the entire pattern [of starting a new thread with an insult, claiming that no-discussion is the "professional approach", with their own opinion as "the obviously correct answer, case closed"] is a very sore button.)

I really, really hate such detestable attempts at social manipulation.

To me, the entire discussion is a bit funky, because as nctnico said,

IMHO the whole point is to understand when a simplification works and when not.

and this observation should also be extended to the model used to describe a situation.

One thing I absolutely love about physics simulations is that no matter what you do, the first step when you get some results is to analyze whether it makes any sense.  A part of that is to guesstimate the various factors (say, to within a few orders of magnitude), whether the model includes everything that should be included, and so on.  Only a small part of that is estimating the approximations used; it is the appropriateness of the model used that is the key.

I do find it interesting that the skill of shifting ones mind across model complexity levels is relatively rare.  In programming, I've seen flamewars between top-down (starting with an overall plan, and finishing with actual code) and bottom-up (starting with actual code, then connecting them together, to build a larger more complex whole) approaches, that completely baffles me: I proceed with the hardest problems first, until I can build a reliable model of the end result, happily skipping between complexity levels as needed.

I can see exactly why the same would happen with those who are used to treating everything as a field, and those who work with circuits.

Perhaps it is too hard for most humans to encompass both at the same time –– it is to me, that's why I have had to learn to skip and switch as needed ––, but assuming ones favourite model suffices everywhere is ... well, insufficient/wrong/silly.  In physics simulations, one would trip on it immediately, and fail.

Molecular dynamics is an excellent example.  If we take only the outermost interacting electrons in atoms, and model the rest of the atoms (both nucleus and the rest of the electrons) as a single point charge, and only consider the rest states of each atom, we can model all chemical bonds to a very high degree.  (The charges themselves are modeled as quantum mechanical waves, see e.g. Hartree-Fock method; this is why these simulations are called "quantum mechanical" or "ab initio", starting from the simplest possible interaction model.)

However, the math is so onerous, that even the largest supercomputers have issues with more than some thousands of electrons.  Simplify the interaction model, for example via Embedded Atom Model for metals (albeit you need multi-band EAM for some metals like ferrochrome), and you can model millions to billions of atoms, and get essentially the same results.

Which one is correct?  Well, neither, because both are approximations.  For some systems, both are precise enough to yield useful information, and are used every day in materials research (even in now-mundane things like thin film tech, ion implantation, and so on).
(And yes, there are lots of QM/ab initio simulators using VASP or Dalton, and scoffing on those who use classical potential models or force fields (naming varies between physics, chemistry, and biology, even though they all do more or less similar simulations).  It, too, is horribly silly.  And very often leads to someone, usually an established professor, making an argument from authority, which is even more disgraceful.)

[Simon]

In reality, the fact is there is no large dispute.

Once I figured that out I tried--rather clumsily I suppose--to point out what I saw as the primary issue leading to the disagreement and later the misdirection of attention as to which 'path' was important--it took me a bit longer than I'd like to admit to catch onto this--that sort of made it look like a much more noteworthy issue than it really is.  But the main contestants weren't interested in any of that, just proving that they were superior and engineers are stupid.  And then along came some additional contestants to confirm that. 

The OP in this thread has a reasonable, short explanation for those that don't want to read 39 pages of name calling and drivel.  However, I would replace

So, any time we have a changing field or current (e.g. AC at any frequency), we can no longer define voltage.

with "there are multiple possible definitions of voltage" or something like that.  Proving that we can't define voltage by measuring something with voltmeters seems a bit silly.

The problem is that thanks to certain not as prolific as the masses think and misguided public figures ventures, engineering is now "cool" and the bar for interest has dropped down very low and suddenly every idiot that usually would be more interested in posing down the local pub to attract girls thinks he is an expert because he saw a video made by someone as dumb as them that explained it for them.

[Siwastaja]

I don't think it's a sock puppet account, the writing style does not seem to match with anyone. OTOH, I'm not an expert in analysing human communication, so could be wrong. It could be a sockpuppet with careful change in writing style. Maybe an actual expert can chime in, if we have one.

The fact that the poster has 1 post is not surprising. Because the matter is discussed outside of EEVBlog forum, it brings people in when they notice it's being discussed here. Has happened before.

In any case, it's up to Nominal Animal to prove his claim that this is a sockpuppet account. Do you actually have some information we others don't? Or are you just participating in these name calling social games you so much hate? Calling one a sockpuppet is no different from any other name calling that's going on. And don't get me wrong, I totally see the point, I hate social games too, but you must admit they sometimes just suck you in - and it doesn't make you feel good about yourself.

Regarding social manipulation, this is what I hate above all, and having had about three years to think about this, I'm becoming more and more certain that social manipulation is exactly what Mehdi originally did, and did it really really well. This is difficult to say for me because I have been quite entertained with Mehdi's videos, admired his down to earth style of teaching basic electronics and related physics, and always thought he's a very decent human being, and the last person to play such social games.

On the other hand, worst social manipulators tend to be among those who appear very positive, appear to hear everybody out and have a balanced discussion, appear easily approachable. This isn't a surprise, because if you are nasty and call others with names, who's going to believe you and fall into your social trap? No one. Successful social manipulation needs to be hidden. What we see in the current thread of 40+ pages, isn't social manipulation; it's just gang membership, namecalling, generally behaving like little kids, with some physics education thrown in. However, we can assume that social manipulation is what started it, not a coincidence. This is a fair assumption because the Lewin's experiment has been widely known for decades; nothing changed. What suddenly made it controversial? So who manipulated people into this? There are not too many options. Maybe Lewin, by posting thousands of hours of physics teaching videos from 1990's - early 2000's, hiding a manipulation attempt in one, to have it triggered two decades later? Is this realistic? So I think, if successful, actual social manipulation is part of this, there are no other viable perpetrators than Mehdi. He has to be at the root, and if not, no one is, it is then "just happening".

I also think another massive contributing factor was Lewin's initial response to Mehdi. This reponse was, IIRC, quite nasty and totally unhelpful, and something a good teacher should never let slip. It sure helped create the impression that "Mehdi has to be right", and strengthen the Mehdi followers, initially me included (until I finally got over it, and started thinking about the experiments and physics itself. Again, the eye opening moment was when I admired the amount of effort put in to the exact layout of the experiments (think Mabilde), and then bang, I realized that circuit layout is different from "good probing"; and "good probing" alone didn't provide the expected results. And that layout wasn't described in the equivalent circuit diagrams).

In other words, Mehdi's behavior, at least on surface, was better than Lewin's. Which is also exactly why, if I have to place bets on who's the social manipulator, I will vote Mehdi. And now, this is getting a bit far-fetched, but if Mehdi's a real social manipulator, then he has also known beforehand Lewin's personality (which is all over his videos), and knew that: "buahaha, I will win if I keep my head cool, make my opponent angry by pulling the right knobs, so that he slips out insults; then I only have to ask a few professors to assess my claims, and get a report I can quote out of context."

This is still not to say I'm 100% sure Mehdi is a social manipulator. I'm still 50-60% about this, and I will never be sure about this. Maybe things just went the way they did, with no bad intentions. But think about it!

[HuronKing]

In other words, Mehdi's behavior, at least on surface, was better than Lewin's. Which is also exactly why, if I have to place bets on who's the social manipulator, I will vote Mehdi. And now, this is getting a bit far-fetched, but if Mehdi's a real social manipulator, then he has also known beforehand Lewin's personality (which is all over his videos), and knew that: "buahaha, I will win if I keep my head cool, make my opponent angry by pulling the right knobs, so that he slips out insults; then I only have to ask a few professors to assess my claims, and get a report I can quote out of context."

This is still not to say I'm 100% sure Mehdi is a social manipulator. I'm still 50-60% about this, and I will never be sure about this. Maybe things just went the way they did, with no bad intentions. But think about it!

What's irritating is that Mehdi didn't even wait for Dr. Belcher, whom Lewin suggested he go talk to, to answer his questions before releasing his initial video accusing Lewin of 'bad probing.' I could see why Lewin would be dismissive of Mehdi at face value, and then become outright contemptuous of Mehdi claiming an MSEE while refusing to see something that a 2nd year physics student learns (that line integrals are path dependent in non-conservative fields, the end). Did Mehdi even watch any of Lewin's other lectures in the course? Don't know!
Then add onto it Mehdi's legions of literally millions of subscribers bombarding Lewin with hate-mail... and taking a victory lap and dragging Feynman along for the ride... it's really too much.

And this is more than just a stupid internet drama to me. I am an EE educator. I teach power and motor lab courses and I ALWAYS have a handful of students who have seen Mehdi's videos on KVL and need to have the pseudoscience shaken out of their heads and so I include a vector calculus review and thorough discussion  of Romer's paper as my first lecture.
 

[Simon]

Unfortunately the electroboom channel speaks to the lower levels with it's constant epileptic fit provoking gags. This is why it's not a good idea to get more people into the field by appealing to their stupidity. You need to make sure the capable are given the chance no matter their socio economic standing. Then you will collect more. The people that electroboom's videos appeal to should maybe abstain from procreating!

[tszaboo]

Guess what, KVL also doesn't hold, when a wire is hot, and thermionic emission happens.
It doesn't mean it is useless. And who cares. Let grey haired physics professor rant on their own lectures. When I had a prof like this at university, I just stood up and took the class with another one, that was an engineer.

[Nominal Animal]

In any case, it's up to Nominal Animal to prove his claim that this is a sockpuppet account. Do you actually have some information we others don't? Or are you just participating in these name calling social games you so much hate? Calling one a sockpuppet is no different from any other name calling that's going on.

Dammit, you're absolutely right.

I guess certain words in the title ("ridiculous") and initial post ("nerd") just hit me in a sore spot.  I find the original topic interesting (because there is no simple answer, since both approaches involve modeling the situation in a specific way, and it just isn't possible to say that one is superior to the other –– they are simply appropriate in different contexts), and maybe the combination of perceived insult and social manipulation tactics pushed me over the edge... but I do acknowledge that I have not contributed positively to the topic, and this is purely my own mistake and error, and I do apologize.

(I do see the pot-kettle-black on my part here, too: I essentially made the same error as the OP of this thread.  I have no proof OP had any kind of manipulative intent.  Apologies for that, too. )

[HuronKing]

Unfortunately the electroboom channel speaks to the lower levels with it's constant epileptic fit provoking gags. This is why it's not a good idea to get more people into the field by appealing to their stupidity. You need to make sure the capable are given the chance no matter their socio economic standing. Then you will collect more. The people that electroboom's videos appeal to should maybe abstain from procreating!

Indeed it does, but his narrative is seductive, even to budding engineers.

"Lewin is an egg-headed physicist who doesn't do anything practical unlike us manly-men practically practical engineers!"

Meanwhile, I'm there thinking,
"Uhh... none of us could even take an Applied EM or a Motors course without first passing the MIT 8.02 equivalent..."

And don't get me wrong. I used to wear my Full-Bridge Rectifier T-shirt because his shtick was funny and he wrapped up some nice rudimentary lessons in slapstick comedy.

But nowadays I use his channel as a case study for my students about engineers becoming susceptible to pseudoscientific notions.

I didn't even understand exactly what Lewin meant when he called Mehdi a Flat-Earther, but now I do.
For most navigational purposes, we consider the Earth to be flat. It's a good approximation. No one takes the curvature of the planet into consideration when driving to work. 99% of the time - we are Flat-Earthers in practice, even if we pay lip-service to believing in the sphericity of the Earth, none of us need to know that in our daily lives.

But that 1% of the time, when we step onto an airplane to fly across the planet, NOW the curvature of the Earth matters. So, we need spherical Earth science to navigate properly.

KVL is our Flat-Earth approximation. Faraday's Law is the spherical Earth.
KVL is just a special case of Faraday's Law and only holds in specific conditions and assumptions. Just like our spherical Earth can be considered to be locally flat under the right conditions.

But when Mehdi claims KVL ALWAYS HOLDS... he's saying the Earth is always flat, all the time. And so now I share Lewin's outrage at Mehdi telling millions of viewers that the Earth is always flat... err... that KVL always holds.

[Simon]

If I remember rightly it was lewen that tried to show the theory does not hold up by going beyond it's scope. As much as I respect the man as an inspiring lecturer in this case he delved into something outside of his sphere and did not make clear why it was happening.

[Siwastaja]

A really good teacher needs to keep their head cool in case of objection, and continue the quest of making people learn; spend all the time necessary to help student find the source of their error. Lewin colossally failed in that, possibly because of personality issues, possibly because he did not consider Mehdi as his students. But there is a third possibility, that he understood from day one that Mehdi's being intellectually dishonest with no intention of learning, and "skip" the whole game as unfruitful waste of time. Such is risky behavior, but so is sexually harassing one's students. Lewin's definitely is not a model character. When you say it like this directly, everybody will agree that it's irrelevant when it comes to the physical discussion. Yet, it's very usable tool to create suitable impressions. Lewin's not trustable. Mehdi's a very nice guy, who just makes a rational argument...

Guess what, KVL also doesn't hold, when a wire is hot, and thermionic emission happens.
It doesn't mean it is useless. And who cares. Let grey haired physics professor rant on their own lectures. When I had a prof like this at university, I just stood up and took the class with another one, that was an engineer.

This comment is fascinating, I think it kind of proves my point exactly.

Imagine Mehdi's video never existing in a first place.

I'm rephrasing tszaboo's comment in my own words, and I hope I don't significantly change the meaning, as if this comment appeared after attending Lewin's lecture with the demonstration shown:
"Oh, Lewin demonstrated a case where KVL does not hold, I understood it, and it's correct. There are other cases where KVL fails, too, like thermionic emission. So what? No one ever called KVL useless, but I still want to make it super clear, that it is not useless. I don't like the character of Lewin and due to that, will prefer other lecturers."

See how ridiculous this is in this changed Mehdi-free context? Lectures are full of demonstrations. I have never heard anyone say "so what, there are others as well".

But we see many comments like tszaboo's, and why is that? Because a straw man exists, a straw man of "KVL being useless", which is just ridiculous, no one ever claimed that. This strawman also includes the idea that Lewin somehow claimed that KVL is unusable for most everyday engineering tasks, or something like this.

This strawman is especially appealing to those who never attended university, and as a result, not understand basic university-level mathematical notations and more importantly, admit the importance of basic terminology. Which is fine, but Lewin's lecture videos are in university context. Mehdi's reply isn't.

But this strawman clearly is also appealing to some who did attend university, like tszaboo, or myself.

But where did this strawman originate? I'll give tszaboo benefit of doubt, his intentions are at least neutral.

Hence the "Mehdi's a social manipulator theory". Believe it or not, it's not important, but important is to think what's happening.

[instrumental]

Hey folks!

Any sensible comment gets lost in the noise in a matter of a day, which is probably exactly the reason for such smoke screen.

What will prevent this thread also suffering the same fate once it's been discovered?

If someone is disrupting a discussion through foul means then surely the answer is to ask a mod to deal with them. I don't see that giving them more threads to disrupt achieves much. Of course, perhaps the mods will be too busy, fail to see your point or otherwise let things run, but you don't know unless you ask.

But, on the whole, I am not averse per se with skimming the crust off into another smaller and newer thread. It was just the "Listen, my explanation is the right one, so I'm a special case" which poked me.

Firstly -- no, I'm not a sock-puppet, I'm a longtime lurker who happened on this thread yesterday while skiving off documentation. I'd already been somewhat aggravated at the YouTube scene over this dispute, and made an account to post about this (and also to complain about the SCPI interface on the RS-KEL103, but that's another matter). Nice to meet you all :-).

Secondly -- yes, it's a bit presumptive of me to come and post an "authoritative" explanation instead of posting in the other thread, where it would be more on-topic. Firstly, I was hoping more for a meta-discussion about the argument, and wanted to bracket off the problem itself. Secondly, I'd like to understand what exactly about this problem is so tricky to understand; if my explanation of the problem is unsatisfactory, perhaps you have a more intuitive explanation.

We've gone this way now, and I'm happy to be having this discussion. Please excuse me! I lost the plot a bit, writing the screed, then (in a slightly hungover state) forgetting to return to the raison d'etre of the thread in the first place -- asking why this disagreement is occurring, and what can be done to put an end to it.

If I remember rightly it was lewen that tried to show the theory does not hold up by going beyond it's scope. As much as I respect the man as an inspiring lecturer in this case he delved into something outside of his sphere and did not make clear why it was happening.

Lewin's demonstration is not the clearest. I'm still scratching my head over it! Most of his demos are excellent; this is trying to demonstrate a counterintuitive phenomenon with counterintuitive, roundabout testing. I think this also leads to so-called"experimentalists" changing the free parameters of the demo and disagreeing about the interpretations of the results -- a sign of a bad experiment!

Perhaps to sketch an alternative, I'd opt to attach the ground clip to the tip of an oscilloscope probe and demonstrate that I can still sense "voltages" when time-varying magnetic flux is running through the loop -- it's a handy trick to know for qualitative EMC, and simple enough that the odd interpretations around Lewin's demo ("what if we move the resistors around the loop") are evaded. No free parameters this way, hard to get it wrong :-).

A really good teacher needs to keep their head cool in case of objection, and continue the quest of making people learn; spend all the time necessary to help student find the source of their error. Lewin colossally failed in that, possibly because of personality issues, possibly because he did not consider Mehdi as his students. But there is a third possibility, that he understood from day one that Mehdi's being intellectually dishonest with no intention of learning, and "skip" the whole game as unfruitful waste of time.

This is a great point. From Lewin's perspective, this is a settled matter; EM theory has hung around for over a century, and he'd been working in the field for over half a century at the time. He runs into the issue of communication with a student who doesn't quite get it. It's made more difficult by the fact that Mehdi himself is positioned as an educator, who frames "disagreeing with a master" as regular in the ordinary course of science.

So, any time we have a changing field or current (e.g. AC at any frequency), we can no longer define voltage.

with "there are multiple possible definitions of voltage" or something like that.  Proving that we can't define voltage by measuring something with voltmeters seems a bit silly.

I appreciate this! I meant this more in the context of the definition of the voltage as the potential function of the electric field (in which case the maths breaks) -- this should definitely be clarified. Thanks!

Many thanks for the discussion, all!

[RoGeorge]

Might be Prof. Lewin's account.   

Can't tell about others, but I'm very well and happy about my nerdyness.  To me, being called a nerd is a compliment, thank you! 

About Prof. Lewin, I think he is correct, no doubt for me now.  Makes sense in every aspect I am aware of, thought I'm only an amateur physicist.

At first, my "mind conditioning" unintended induced by years of tinkering with electronic circuits made me think Mr. Lewin was joking, especially since one of his papers about the subject was dated 1st of April. 

But then, I've put aside the EE approach and tried to look only in terms of physics laws and physics and definitions (Voltage is the work needed to drag a charge from A to B), and it was clear like day and night that the professor is correct.  Also, what he was pointing out and his mind blowing demonstration doesn't brake Electrical Engineering in any way.

EE deals with the same results by "blaming" the induction in the voltmeter's cables.

Overall, I'm grateful he pointed out to non-conservative fields with a click bait title and a mind blowing experiment.  Otherwise I would have missed that aspect of non-conservative fields entirely.  Though, the biggest lesson to me was how strong brainwashing can be (here a case of unintended brainwash).

The strongest cage to break is the mind conditioning that slowly grows to imprison us.

[Simon]

My memory is that Lewin demonstrated that the law did not hold, but gave no further explanation as though he had proved someone wrong. As a lesson that is a failure.