Author Topic: #562 – Electroboom!  (Read 105914 times)

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Offline Sredni

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Re: #562 – Electroboom!
« Reply #500 on: November 29, 2021, 05:04:24 am »
Once again, what is the value of VAD?
Once again:
It depends on the path.

How did place the probes to measure it? Midway through the disk, because you chose an highly symmetrical setup?
How would you place the probes in the solenoid was made in triangular shape and the ring with the resistor shaped as Mickey Mouse's head silhouette, tilted and off-center?
Nope, the voltage VAD is ALWAYS -96mV.  I asked you to calculate it, not to measure it. 
And I am repeating you, in size 18pt, 24pt, 36pt, that it depends on the path. So, in order for me to calculate it, I need to know the path (actually it suffice to know how it partition the flux region). Because voltage is a path integral and in the presence of variable magnetic field, per Maxwell equations, it does depend on the path. I know you don't like it and you want to consider the scalar electric potential difference, instead, but if we use different definitions, you have to accept we have to use different methods.

But the really funny thing is that if I gave you a strangely shaped coil and a strangely shaped circuit *you* would not be able to compute your version of voltage, nor to find the special path your probes should be positioned in order to measure it because all your computations so far are based on the assumptions of a constant induced Eind field that follows your coil's profile.
(Someone else, who could compute the fields and eventually simulate them numerical would, but you? I doubt it)

My method, on the other hand, only require for me to know how the path you want voltage to be computed on (because - it - is - a - path - integral - that - depends - on - the - path) partions the flux region. Half and half? Two-thirds, one thirds? Three-fifths, Two-fifths? Using the integral version can be very easy.

What I am trying to tell you, and I know you will misunderstand, is that you will be in breach of the rules set by McDonald for computing the difference in the electric scalar potential (what you call 'voltage' and McDonald calls 'voltage drop').

Quote
For this particular configuration of the problem, it is fairly easy to setup the probe so that the external magnetic field does not induce a voltage on it.  The calculation perfectly matches the measurement. 

And I don't know how many times I had to repeat this: both parties will get the same results for the measurements by actual voltmeters.

Quote
When Lewin did his experiment with a similar shape, he did not extract the correct equivalent circuit, and then he couldn't figure out what VAD was, so he blamed KVL.

Because Lewin uses the definition of voltage that is used by Purcell, Ramo Whinnery Van Duzer, Brandao Faria, Haus and Melcher, Rosser, Romer, Nicholson, and a ton of other textbooks and universities. Oh, yes, and by your voltmeters and oscilloscopes. That's what they measure.

When Mouser or Farnell or Arrow will start to sell voltmeter capable of measuring the McDonald voltage, we can talk again. For the time being, the Helmoltz decomposition for quasimagnetostatic problems is a nice mathematical trick but a definition of voltage that breaks Ohm's law and makes your students revert back to the  high school mindset where "nonconservative fields are not in the final" is just a bad idea.
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Offline Sredni

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Re: #562 – Electroboom!
« Reply #501 on: November 29, 2021, 05:22:29 am »
"What about the other forms of EMF, uh, what about 'em(f)?"

A common objection raised by KVLers is that Kirchhoff Voltage Laws was originally intended to include all forms of electromotive forces, including the nonlocalized inductive EMF. They mention the high school version of KVL that puts all EMFs on one side of the equation and all voltage drops on the other. From their point of view, considering the inductive EMF as a special case, would imply having a new law for every new kind of localized EMF in the loop. The problem is that the inductive EMF is a very special kind of EMF that is not like other forms of EMF.

If we go back to the original formulation by Kirchhoff in the 1845 Annalen der Physik und Chemie,


link https://i.postimg.cc/5tzVMxGx/screenshot-2.png
https://books.google.de/books?id=Ig8t8yIz20UC&pg=PA494&hl=de&source=gbs_toc_r&cad=3#v=onepage&q&f=false:

he indeed wrote (I am using R instead of omega to denote the resistance, and n instead of nu):

Quote
2) wenn die Drahte 1, 2, n, eine geschlossene Figur bilden

          R1 I1 + R2 I2 + ... + Rn In

= der Summe aller elektromotorischen krafte, die sich auf dem Wege: 1, 2, n befinden; wo R1, R2, Rn die Widerstande der Drahte, I1 I2,... die Intensitaten der Strome bezeichnen, von denen diese durchflossen werden, alle nach einer Richtung als positiv gerechnet.

Which translates into (bold mine)

Quote
2) if the wires 1, 2, n, form a closed figure

          R1 I1 + R2 I2 + ... + Rn In =

= the sum of all electromotive forces located on the path: 1, 2, ...n;
where R1, R2, ... Rn are the resistances of the wires, and I1 I2, ...In denote the intensities of the currents that flow through them, all calculated as positive in one direction.

Automatic translation is getting better and better every day, thanks to AI progress. Here is Google Translate's output for the original German text:


link https://i.postimg.cc/CLJMvxyX/screenshot-3.png

The locution "located on the path: 1, 2, n" points to sources of EMF located on the path itself and I have found at least one source confirming that Kirchhoff formulated his rules by using localized, lumped, forms of EMF. In his Physics Education paper "Explaining electromagnetic induction: a critical re-examination. The clinical value of history in physics" (J Roche 1987 Phys. Educ. 22 91), science historian J. Roche writes:

Quote
"It was shown by G Kirchhoff (1824-87) in 1849 that localised EMFs generally set up auxiliary electrostatic forces, by means of surface charges, in order to establish a uniform current around the circuit (Kirchhoff 1879 pp49-55, 1514). Since these additional fields are conservative, the sum of the net potential differences around the whole circuit will be exactly equal to the sum of the PDs across the localised underlying EMFs only. This is the substance of Kirchhoff’s second network law (Kirchhoff 1879 pp 15-16)"


At the time the sources of EMF were galvanic cells, chemical batteries and thermopiles, like the state of the art electricity source used by Ohm to estabilish his law: a thermocouple based on the Seebeck effect (Ohm experimented in 1827, was basically discredited by Georg Pohl, and later 'rediscovered' in 1841, when the Royal Society (in London) awarded him the Copley medal in recognition of his accomplishments).

According to the above text, the right hand side of Kirchhoff's original KVL equation collects (with due sign) the contribution of all the lumped EMF sources that are present along the path (on the path, on the way, "auf dem Wege"). He even specifies "all electromotive forces located on the path 1, 2, ... n", the segments into which the path (the CLOSED FIGURE) has been partitioned.


Original KVL with modern terminology
Fast forward to the twentyfirst century, where we know something more about fields and we can even extend Kirchhoff's law to work in the presence of variable magnetic fields (but only when we can lump the inductive EMF along the path).

First, let's rewrite Kirchhoff's equation by making all EMFs located on the paths 1, 2, ... n explicit, by calling them emf1, emf2, ... emfn. If one branch has no localized EMF in it, then the corresponding emf will be zero; the same can be said for the resistances. In its expanded form, Kirchhoff's original KVL becomes:

          R1 I1 + R2 I2 + ... + Rn In = emf1 + emf2 + ... + emfn

where the emf1, emf2,... emfn are the localized electromotive forces located on the segments 1, 2, ..., n of the closed path.

Now we take the localized EMFs of each branch that are on the right hand side and we bring them on the left hand side. The change in sign reflects that different sign convention we use for generators and for passive elements.

            (R1 I1 - emf1) + (R2 I2 - emf2) + ... + (Rn In - emfn) = 0

This is the modern equivalent form of KVL as Kirchhoff formulated it.

In the twentyfirst century we recognize that each term in parenthesis represents the path integral of the total electric field along each of the segments 1, 2,... n, in which the closed path has been partitioned. Therefore, in modern terms, the original formulation of KVL says

             Sum of path integrals of Etot.dl along the branches of our closed figure = 0

The right hand side is ZERO because we have already accounted for all "der electromotorischen Krafte, die sich auf dem Wege" - all the electromotive forces on the branches 1, 2,... n - and because Kirchhoff did not consider any delocalised source of inductive EMF (basically, he was experimenting with batteries and thermopiles). Since the path integral along a closed path is the circulation, in modern notation the original form of KVL can also be written as:

             circulation of Etot.dl = 0            (this is KVL as formulated by Kirchhoff)
                                         (all localized EMF appear in the path integral)


Faraday's law introduces an EMF that is not on the path
Faraday discovered, in modern terms, that the circulation of Etot.dl can be nonzero, if there is a variable magnetic flux cut by the surface formed from the closed figure 1, 2, ... n Kirchhoff was arguing about. According to Faraday's law (not Kirchhoff's law), the circulation of the total electric field along the circuit path is equal to minus the time derivative of the flux of the magnetic field B cut by the surface delimited by said closed path:

           circulation of Etot.dl = -d/dt flux of B   ( this is Faraday slaying Kirchhoff)
                                 (introduces an EMF that does not fit into
                                   the path integral)

Note that the integral on the left still accounts for all der electromotorischen krafte --- I mean, all the localized electromotive forces you can imagine (batteries, solar cells, peltier cells, thermocouples...), but it does not include the nonlocalized inductive EMF due to the flux cut by your closed circuit. Therefore, we don't need a new law for every kind of non-inductive EMF out there: they already are all accounted for in the circulation integral on the left.
The term on the right, on the other hand (pun intended), is a new addition that breaks the original Kirchhoff's law and considerably extends our knowledge of the electromagnetic field. In its local, differential form, Faraday's law states that the electric field curls (i.e. ceases to be irrotational) in the presence of a time-changing magnetic field. This is a general property of the EM field, not just 'another kind of EMF'!

The breaking of Kirchhoff's loop rule is not something Lewin came up with on his own. It's part of standard classical electrodynamics and is commonly acknowledged in EM books for physicists and engineers, for example in Haus and Melcher, Ramo Whinney vanDuzer, Brandao Faria, Rosser...
In particular, a respected introductory textbook that makes this explicit is the second volume of Berkeley Physics: Electricity and Magnetism 3rd edition by Purcell and Morin:


link: https://i.postimg.cc/kGXzD9jR/purcell-faraday-2.jpg
Source: Purcell, Morin third edition, section 7.5

...Kirchhoff Loop rule is no longer applicable when there are variable magnetic fields inside the circuit's premises.


Extended KVL and its limits:
We can even push it a little further and accept in the path integral on the left even lumped inductive EMFs: it's what most textbooks (like Hayt, for example) call "extended KVL". It works when the source of EMF can be lumped and the changing magnetic flux can be hidden inside the component: the key is to alter the circuit path so as to exclude the variable magnetic region from it. Still, this trick cannot possibly work when the EMF is due to the changing flux linked by the circuit path itself (like in the example proposed by Romer and popularized by Lewin). That will kill KVL for good, and we are forced to consider the more general law: Faraday's Law.

(And no, trying to bring the delocalized inductive EMF contribution on the left side and distributing it along the branches won't work and I'll explain why in the post about the 'tiny batteries' model)

I already posted a solved example: Lewin's ring with a battery.
Next stop: the tiny battery model and how it related to the McDonald Manouver.
« Last Edit: November 29, 2021, 04:40:11 pm by Sredni »
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Offline HuronKing

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Re: #562 – Electroboom!
« Reply #502 on: November 30, 2021, 03:45:06 am »
For whatever its worth Sredni and bsfeechannel, I'm grateful for your efforts to continually educate about this topic even if it really seems like the KVLers are just running in circles through the madness inducing Lewin/Romer loop (puns somewhat intended).

And here is something peculiar I noticed in ElectroBoom's video about KVL

Look at what he emphatically states is NOT 'his' definition of KVL (it genuinely pained me to see him put a big X through a time-invariant form of Maxwell's Equations),
https://youtu.be/d-a9Pr2z-qg?t=253

Meanwhile, look at the Feynman Lectures he claimed in previous videos, supports his made up pseudoscientific definition, Section 22-3, Eq. 22.14

https://www.feynmanlectures.caltech.edu/II_22.html

Look at what the line integral of the E-field around a closed path is equal to: the sum of the voltages in the loop. When there are no time-varying magnetic fields, what does that sum equal to? Zero.

So, he's saying that the line integral of the E-field around a closed loop being zero is NOT his definition of KVL... but the line integral of the E-field around a closed loop IS the sum of the voltages around the loop... and if that line integral is zero and path independent, you have KVL.

So, uhh, what is he talking about? More made up science?

And this reminds me of something someone noted last time this came up in a big way. The KVL-Always-Holders have inconsistent explanations amongst one another for why these voltmeters connected to the same point read different values. But when one applies Faraday's Law, one of Maxwell's actual equations, there is no inconsistency in explanation and multiple types of phenomena are easy to explain and model and, yes, reduce to KVL-lumped expressions (as Feynman writes is possible under specific circumstances).
 
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Offline Jesse Gordon

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Re: #562 – Electroboom!
« Reply #503 on: November 30, 2021, 04:22:30 am »
... The KVL-Always-Holders ...

Uhh, I guess when you're done grabbing at straws you can sweep them up and make a straw man  :-DD

I don't know of any KVL-Always-Holders. There's clearly situations where the wavelength is smaller than the apparatus and KVL either would not hold or would be difficult or impossible to demonstrate as holding. There may also other possible cases where it is impossible to demonstrate KVL holding.
We don't say that KVL holds ALWAYS. That's an easy straw man to pick apart.

What I'm saying is the same thing that Physics Professor Dr. McDonald  said: "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."

The really odd thing is the Lewinites refusal to answer simple questions, like I ask below.

Referencing the diagram below, can you answer for me:

1: In a real life experiment, with the shown transformer and resistors and with volt meters at the locations indicated, with the volt meters all triggering their reading at the same time, will the voltages of all 5 volt meters sum to be zero? (Within the accuracy limitations of the meters of course....)

1b: If YES, then KVL at the very least holds. If you say KVL is not holding, explain why it is not holding even when/though it appears to be.

1c: if NO, then what do you think the reading will be and why? Because I will like to test a real world setup and see who's right.

2: Are all the volt meters connected at places which would provide an unambiguous reading of the voltage at the points indicated?

2b: If not, which volt meter would be ambiguous and why?

Basically, my tests show me that the voltages would sum up to zero, like KVL predicts. Snedri and bsfeechannel seem to indicate that KVL is not holding, even though it appears to be, (however they seem very reluctant to actually commit one way or the other on that....)

As far as I can tell, KVL would at the very least appear to hold as measured with a real volt meter, but for some reason, they think it's still not holding, but they seem unable to explain why it appears to be holding when they think it's not.

Is it a technicality? Now I see Snedri going over the original language, I wonder if he's trying to make some argument based on a technicality whereby which he can say that KVL doesn't hold even in cases where it gives every appearance of holding.



I look forward to your answer.

Thank you!
 

Offline HuronKing

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Re: #562 – Electroboom!
« Reply #504 on: November 30, 2021, 04:59:44 am »
"I don't know of any KVL-Always-Holders."

You're not terribly well acquainted with the debate then. ElectroBoom (the guy who this thread is about) literally, and rather triumphantly, declares that KVL holds in all cases, his words (with accompanying fanfare music):
https://youtu.be/Q9LuVBfwvzA?t=838

As for me, I'm not terribly interested in saving KVL or going around in infinite loops with you (which is why I wanted to say my thanks to Sredni and bsfeechannel for their seemingly inexhaustible patience). Besides, KVL is not one of Maxwell's Equations anyway. Faraday's Law is.

On the flipside, no one here is a Lewinite (kind of gross phrasing anyway, as if this is a 'battle of personalities'... but that's what ElectroBoom wanted when he titled his first video "Disagreeing with a Master"). We're just people who have studied Maxwell's Equations. They were around before Lewin was even born, other people have described them well, and they'll be here long after us.
« Last Edit: November 30, 2021, 05:11:36 am by HuronKing »
 
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Offline Sredni

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Re: #562 – Electroboom!
« Reply #505 on: November 30, 2021, 05:45:23 am »
And here is something peculiar I noticed in ElectroBoom's video about KVL

Look at what he emphatically states is NOT 'his' definition of KVL (it genuinely pained me to see him put a big X through a time-invariant form of Maxwell's Equations),
https://youtu.be/d-a9Pr2z-qg?t=253

Meanwhile, look at the Feynman Lectures he claimed in previous videos, supports his made up pseudoscientific definition, Section 22-3, Eq. 22.14

https://www.feynmanlectures.caltech.edu/II_22.html

Look at what the line integral of the E-field around a closed path is equal to: the sum of the voltages in the loop. When there are no time-varying magnetic fields, what does that sum equal to? Zero.

So, he's saying that the line integral of the E-field around a closed loop being zero is NOT his definition of KVL... but the line integral of the E-field around a closed loop IS the sum of the voltages around the loop... and if that line integral is zero and path independent, you have KVL.

So, uhh, what is he talking about? More made up science?

One thing I have noticed with youtubers is they do not allow coherence or logic to get in the way of their videos. And after they reached a certain number of subscribers they can hardly admit their errors. At least Mehdi does not seem to try to defend its blunders in the comment section, like others do (sometimes to the point of banning critics). I am waiting to see if Dave will correct at least the description of his giant errors in the "Electricity misconceptions" video, or if he will let his followers listen to that nonsense about the Poynting vector only pointing outwards at AC and that fantasy connection with the skin effect (why not the proximity effect, then?). And it seems that misquoting Feynman is the ultimate signature of quackery in the EE field.

Quote
And this reminds me of something someone noted last time this came up in a big way. The KVL-Always-Holders have inconsistent explanations amongst one another for why these voltmeters connected to the same point read different values. But when one applies Faraday's Law, one of Maxwell's actual equations, there is no inconsistency in explanation and multiple types of phenomena are easy to explain and model and, yes, reduce to KVL-lumped expressions (as Feynman writes is possible under specific circumstances).

Yes. This and another point bsfeechannel made a few pages ago: you can see KVLers see the light ("IT'S A SAILBOAT!") and turn Faradians, but I have never seen a Faradian who understood Faraday's law ever turn KVLer. That tells a lot. I mean, if you understand Faraday you usually understand the Helmoltz decomposition and you can see what McDonald is doing, so you won't be a KVLer tout-court...

I also get something out of this. A selection of guinea pigs to test for holes in my exposition, required refinement in language (lumpABLE, lumpED, NOT lumped, UNlumpable...), and a stimulus to deepen my knowledge.
For example, I have now a very clear idea about how give a definition of voltage straight from electrostatics (from my 'silent post'), I overcame my 'fear' of partial (even straight, as paradoxical as it may seems) turns, and if need be I feel confident I could operate a 1821 multiplier with embedded bismuth-copper thermocouple (given enough ice and boiling water).
I am also interested in the mechanisms of rejection, cognitive dissonance, confirmation bias, and the like.
Unfortunately the only two KVLers left have lowered the level by several notches, by becoming obnoxiously repetitive...
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Offline jesuscf

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Re: #562 – Electroboom!
« Reply #506 on: November 30, 2021, 06:23:06 am »
I am also interested in the mechanisms of rejection, cognitive dissonance, confirmation bias, and the like.
Unfortunately the only two KVLers left have lowered the level by several notches, by becoming obnoxiously repetitive...

Wow, interesting!  Sredni have you figured out yet how to calculate the voltage between nodes A and D, VAD?  Yes, because you used that voltage to find Vx and Vy, but no, because it completely obliterates all the BS you have posted in this forum about VAD being 'path dependent'!  That is literally the definition of cognitive dissonance!!!   Here, check this link to find out how is properly done, a very simple excercise:

https://www.eevblog.com/forum/amphour/562-electroboom!/msg3842183/#msg3842183

The answer is VAD=-96mV, ALWAYS!  KVL works perfectly!

So far what I have observed with team Lewin is: they don't know how to use KVL ergo KVL doesn't work!!!



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Offline Sredni

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Re: #562 – Electroboom!
« Reply #507 on: November 30, 2021, 06:33:20 am »
GOTO 500
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Offline Jesse Gordon

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Re: #562 – Electroboom!
« Reply #508 on: November 30, 2021, 06:41:23 am »
If you honestly answer the above questions and I'll do my best to draw up Lewin's loop and show how I would measure the voltage across the half turns.

Oh, no. Now you answer MY question, not a question of your choice.
And my question is:

This is Lewin's ring: two resistors in a single loop that goes around a circular region (let's consider it of the same size as the loop, so you can see there is no 'room to twist' the wires) of variable magnetic field. The resistors are required to be on the opposite sides of the variable magnetic field region.


https://i.postimg.cc/kX0TSBw6/Lewin-ring-is-unlumpable.jpg

Please, show everybody you can draw a circuit path (make it green, meaning it's 'flux-free') that joins the resistors' terminals to the "lumped transformer secondary" terminals and DOES NOT INCLUDE the variable magnetic field region in its interior. Like I did for the lumpABLE circuit I decided to see as lumpED (in my post "Lumpable (lumped and not lumped) and not lumpable circuits for dummies").

In addition, you can also show everybody you can draw the path inside your "lumped transformer secondary" that DOES INCLUDE the variable magnetic field region (make it orange) but IS NOT part of the green circuit path.
I will show you that if you can do that you will run into contradiction.

OK here's how anybody can unambiguously physically measure the induced voltage in half of an air-core transformer secondary turn

Nice try, but you did not answer the question.
Let me repeat it for you here, in case you missed:

This is Lewin's ring: two resistors in a single loop that goes around a circular region (let's consider it of the same size as the loop, so you can see there is no 'room to twist' the wires) of variable magnetic field. The resistors are required to be on the opposite sides of the variable magnetic field region.


https://i.postimg.cc/kX0TSBw6/Lewin-ring-is-unlumpable.jpg

Please, show everybody you can draw a circuit path (make it green, meaning it's 'flux-free') that joins the resistors' terminals to the "lumped transformer secondary" terminals and DOES NOT INCLUDE the variable magnetic field region in its interior. Like I did for the lumpABLE circuit I decided to see as lumpED (in my post "Lumpable (lumped and not lumped) and not lumpable circuits for dummies").

In addition, you can also show everybody you can draw the path inside your "lumped transformer secondary" that DOES INCLUDE the variable magnetic field region (make it orange) but IS NOT part of the green circuit path.
I will show you that if you can do that you will run into contradiction.

Please, please, please, do not fly to another galaxy with your armchair before answering it.

I don't know what mushroom induced pipe dream you're envisioning and wanting me to draw up or what imaginary constructs you want me to use.

I can't read your mind. Remember, YOU"RE the Gyspie Fortune Teller with your Crystalball!

I did show how anybody can unambigously physically measure the voltage across a half-turn on Lewin's circuit.

That's my answer. If you don't like it, tough.

For the record, you didn't answer my questions either that were part of this deal. You beat around the bush and refused to actually answer my questions. What recourse do I have? Tough beans is all I got and that's all you got if you don't like my answer.

You answered questions of YOUR choosing, not the ones I asked.

The over arching issue here is that your own trusted source says that if the voltage on the output of an element can be unambiguously physically defined, then KVL will hold.
And I have demonstrated both on paper and in the lab how the voltage on a half-turn of Lewin's circuit can be unambiguously and physically defined and measured.

I agree with Dr. McDonald PhD, Princeton Physics Professor, when he said that 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.

I also agree with Dr. Belcher PhD, MIT Physics Professor, when he warmly thanked Mehdi for his contributions, but said NOTHING of Lewin's -- and when he talked at length about Mehdi's "very nice experiments" but said NOTHING of Lewin, and ended up saying "KVL holds as argued by Mehdi..."



If you want to trade another pair of questions, then that's fine, but you need to provide the diagrams for your questions, like I provide the diagrams for mine.

If you do want to trade another pair of questions, here's my next one:


In the real-world test depicted in the below diagram, will Σ(V1,V2,V3,V4,V5) = 0? (Within the accuracy limits of the volt meters of course....)


https://i.postimg.cc/jdJntBXT/20211128-121506.jpg
 

Offline Sredni

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Re: #562 – Electroboom!
« Reply #509 on: November 30, 2021, 06:52:39 am »
Jesse, Jesse...
I did answer your question related to the previous circuit. I also pointed out that the answer was in the top right corner of my images for Lumped and Not lumped circuits. You seem to think that, because lumpABLE circuits exists and as such can be made lumpED by choosing a suitable circuit path, then there cannot be alternatives.

There are alternatives:

Alternative 1: the lumpABLE circuit itself. You choose another circuit path (for the same set of components and connecting wires!) that does include the variable magnetic region. Your system has now path dependent voltage and is NOT lumped.

Alternative 2: there are other circuits in the universe that are UNlumpable. Lewin's ring is one example.

And the fact that you cannot come up with an answer to my question is proof that you are not able to lump it. Don't feel bad. Nobody can lump that without incurring in self-contradiction. It's not your fault. It's the circuit that's drawn like that.



Now you try to shift the attention on yet another lumpABLE circuit, putting your voltmeters in a manner that imply you prefer to use a circuit path that makes it lumpED. Yes, as a lumpABLE circuit, it can be lumpED. But this does not imply that

1. it can also be seen as NOT lumped, by choosing a different circuit path (same components, same wires, same transformer!)
2. there are other circuits out there that are UNlumpable

I really cannot be more clear than this. Try some vitamins, maybe?

But here's the deal: if you put the numerical values of the voltages read by your voltmeters, I will show you the NOT lumped version of your circuit, so that you will avoid posting it again in the same way you are avoiding my question on how would you lump Lewin's ring.

Deal?

EDIT: grammar and clarification about what values I want you to fill in.
Time to sleep, perchance to die, for me.
« Last Edit: November 30, 2021, 06:58:48 am by Sredni »
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Offline jesuscf

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Re: #562 – Electroboom!
« Reply #510 on: November 30, 2021, 06:57:50 am »
GOTO 500

Can you put all the BS you wrote there in the form of a equivalent circuit and compute VAD?  Because proper calculations, using KVL show that VAD= -96mV.  And guess what, proper measurement show also VAD= -96mV!

Hey, a simpler circuit may be easier for you...  In Lewin's original circuit the one with just only one loop, with an EMF of 1V, 100 ohms resistor to the left, and 900 ohms to the right, do you remember it?  What is the value of VAD in that circuit?  Need help?  Here:

GOTO 392
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Bart: Isn't that the wrong way?
Homer: Yeah, but faster!
 

Offline Jesse Gordon

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Re: #562 – Electroboom!
« Reply #511 on: November 30, 2021, 07:14:30 am »
"I don't know of any KVL-Always-Holders."

You're not terribly well acquainted with the debate then.

The part of this debate I'm involved in has nothing in particular to do with Mehdi. We've been arguing for weeks here about whether KVL holds in Lewin's (and other simple) circuits, regardless of what Mehdi Said he.

Quote
ElectroBoom (the guy who this thread is about)

Sure, the thread has that title. But that's not why I'm here. Believe it or not, I did not know Mehdi was involved in this debate until after I got involved.

About a year ago I was happily watching Lewin's Lectures when he got to that part 16 and did his trick with the solenoid. I thought "What's he doing? That makes no sense." I left a comment to his video, and of course his fans started arguing with me, so I made this video: https://youtu.be/nAsZFP8Cfxk

I didn't even know Mehdi was involved in this until after I published my video and then people were like "Oh yeah, Mehdi showed that too" so that's how I found out.

Quote
literally, and rather triumphantly, declares that KVL holds in all cases, his words (with accompanying fanfare music):
https://youtu.be/Q9LuVBfwvzA?t=838

Literally, yes, but not in context. If you watch the whole video, he's talking about a variety of different cases which he demonstrates - AND - he runs his cases by Dr. Belcher, who writes up a nice writeup about a bunch of Mehdi's experiments, and then concludes that "KVL holds as argued by Mehdi."

So the CONTEXT was that of all the different example circuits that Mehdi gave to Belcher, Belcher said that KVL holds for all of them. Which is what Dr. Belcher said.
And Dr. Belcher even quoted Dr. Feynman.

Neither Belcher nor Mehdi are saying that KVL holds for every possible circuit of every possible configuration, but rather that it holds for all the ones they've just examined.

By taking Mehdi's words out of context, you make him out to say something completely different than he was actually communicating.

Your strong negative bias shines like the sparks off Mehdi's fingertips, and smells like his burning clip leads.  :-DD

Quote
As for me, I'm not terribly interested in saving KVL or going around in infinite loops with you (which is why I wanted to say my thanks to Sredni and bsfeechannel for their seemingly inexhaustible patience). Besides, KVL is not one of Maxwell's Equations anyway. Faraday's Law is.

And that's what I get far and wide. The people arguing for Lewin being right are dreadfully reluctant to actually show that they can do real physics. See how you side stepped my question?

They claim to know it all, but can demonstrate none of it, except they are sure about one thing, and that is Lewin was right.

Quote
On the flipside, no one here is a Lewinite (kind of gross phrasing anyway,
What would you call them? They call us "KVLer's" or "KVL-ALWAYS-HOLD"ers or whatever.

I know in your one-sided view  you're right any all who disagree with you are wrong.

But that cuts both ways. There are no KVLer's here, just people who understand physics. Anyone who disagrees is a Lewinite.

See? Either one of us can step outfrom behind a "title" and just put a title on the other side. Doesn't solve much though.

Point is both sides think they are right and the other is wrong.

Quote
as if this is a 'battle of personalities'... but that's what ElectroBoom wanted when he titled his first video "Disagreeing with a Master").

We're just people who have studied Maxwell's Equations. They were around before Lewin was even born, other people have described them well, and they'll be here long after us.


Yeah, there are no KVLer's here, we're just people who know physics!  :-DD :-DD :-DD

I know that air core transformers existed long before Lewin, but I think Lewin was just who really made the party trick well known - the combination of his entertainer style and youtube publicity was what it took to spark it off.

As for how I got here - someone posted my video here, and Thinkfat then went to tell me I was wrong in the comments of my video, and then linked me back to here.

So you like Anti-KVLer better than Lewinite? I don't particularly care. We say "Lewinite" because "Lewin is right" seems to be the only thing that they are absolutely sure of.

I have asked so many times the question I asked you, and like you, they don't mind arguing for weeks, but they don't want to take the time to answer that question.

At the end of the day, in the diagram I provided below, the voltages sum to zero. KVL does hold. Why they can't admit at least that the voltages sum to zero,  I don't know, it's as if they feel it would be reverent to Lewin to admit to it.

 

Offline jesuscf

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Re: #562 – Electroboom!
« Reply #512 on: November 30, 2021, 07:16:51 am »
I did show how anybody can unambiguously physically measure the voltage across a half-turn on Lewin's circuit.

And a quarter turn or any fraction of a turn by that matter!  The blockheads in team Lewin don't want to accept that.
Homer: Kids, there's three ways to do things; the right way, the wrong way and the Max Power way!
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Offline Jesse Gordon

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Re: #562 – Electroboom!
« Reply #513 on: November 30, 2021, 07:39:21 am »
Jesse, Jesse...
I did answer your question related to the previous circuit. I also pointed out that the answer was in the top right corner of my images for Lumped and Not lumped circuits. You seem to think that, because lumpABLE circuits exists and as such can be made lumpED by choosing a suitable circuit path, then there cannot be alternatives.

There are alternatives:

Alternative 1: the lumpABLE circuit itself. You choose another circuit path (for the same set of components and connecting wires!) that does include the variable magnetic region. Your system has now path dependent voltage and is NOT lumped.

Alternative 2: there are other circuits in the universe that are UNlumpable. Lewin's ring is one example.

But I'm asking a yes or no question, and you're saying everything other than yes or no.


Quote
And the fact that you cannot come up with an answer to my question is proof that you are not able to lump it. Don't feel bad. Nobody can lump that without incurring in self-contradiction. It's not your fault. It's the circuit that's drawn like that.

No, it means you're not explaining your question. You're asking me to draw something you're picturing in your mind. I did what I thought you wanted - I illustrated how to unambiguously physically measure the voltage across the half-turns in Lewin's experiment which would allow the loop to be modeled as 4 lumped elements consisting of two half turns in series with two resistors, and if that's not what you're asking then you need to get off the mushrooms and try explaining it more clearly, that, or draw your own diagrams.

Quote

Now you try to shift the attention on yet another lumpABLE circuit, putting your voltmeters in a manner that imply you prefer to use a circuit path that makes it lumpED. Yes, as a lumpABLE circuit, it can be lumpED. But this does not imply that

1. it can also be seen as NOT lumped, by choosing a different circuit path (same components, same wires, same transformer!)
2. there are other circuits out there that are UNlumpable

I really cannot be more clear than this. Try some vitamins, maybe?

My question is a simple yes or no question. Either the volt meters will sum to zero or they won't. Or maybe you think they might some days depending on the phase of the moon.

Quote
But here's the deal: if you put the numerical values of the voltages read by your voltmeters, I will show you the NOT lumped version of your circuit, so that you will avoid posting it again in the same way you are avoiding my question on how would you lump Lewin's ring.

Deal?

EDIT: grammar and clarification about what values I want you to fill in.
Time to sleep, perchance to die, for me.

I already showed you how I would lump Lewin's ring.

I don't understand the exact meaning of the deal you're offering. But I will not agree to refrain from posting something I think is true and on topic, and it looks like you might be asking that in your deal, so no deal. I do not give up any privilege to post what I think is the truth on the matter.

If you want me to stop posting a particular diagram, you need to convince me it's false.

Deal?

I got a better deal: How about you explain to me why you think that KVL is failing even though the volt meters say it's not in my diagram below.

I've literally asked that question to 4 Anti-KVLers on this thread and exactly zero of them have actually been willing to so much as agree that the volt meters will sum to zero, much less explain why they think KVL isn't holding.

It's pretty clear by your trusted source that since all 5 of my elements have their voltage unambiguously physically defined that KVL will hold.


https://i.postimg.cc/jdJntBXT/20211128-121506.jpg

 

Offline Jesse Gordon

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Re: #562 – Electroboom!
« Reply #514 on: November 30, 2021, 08:03:58 am »
 

Offline Jesse Gordon

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Re: #562 – Electroboom!
« Reply #515 on: November 30, 2021, 08:47:29 am »
I did show how anybody can unambiguously physically measure the voltage across a half-turn on Lewin's circuit.

And a quarter turn or any fraction of a turn by that matter!  The blockheads in team Lewin don't want to accept that.

Exactly.

And whether you want to think of the fractional turn in terms of turns under Faraday's law, or as half of the dB/dt area, it all works out the same - that dB/dt area is the area which contributes to the induced voltage across that section of winding. The dB in that area not the dB outside the area.

Then they posted that textbook page which says that KVL holds if the voltage across the terminals can be unambiguously defined by physical measurements - and by George - we seem to be unambiguously defining the voltages by physical measurements, so I say it's time we all agreed that KVL holds for Lewin's circuit!  :-DD

This is getting fascinating.  How is it possible that they know enough to avoid answering numerous questions, but not enough to know that they look clueless?
The fact that they refuse to answer so many questions tells you they know their paradigm is not coherent with itself.

At the very least, How can they not realize that to us they look just as mislead as we look to them?

And what's with the idea that they can just say "There's no team Lewin, just team truth and you're wrong" - how's that any different than us saying "There's no team KVL, we just know the truth and you're wrong?" or "There's no two sides, we're right and you're wrong?" That's some deep thinking!



I can imagine there being an incredibly intelligent person knowing TONS of stuff which I don't understand.
But I cannot imagine that person using such flimsy fallacies as seem rampant on the part of Team Lewin.
Nor can I imagine such an incredibly intelligent person being afraid to answer simple yes/no questions.

When I'm in a disagreement like this, I am constantly aware that I could be wrong and I may just not understand enough to see that I'm wrong, so I look for clues to help me understand whether maybe the other side is right even though I don't understand. One of the things I look at is their willingness and ability to answer questions at a level I can understand. In this case, zilch. Another thing I look at is the quality of their arguments - and again, zilch. Saying things like "There aren't two sides, you're just wrong," or "They are all dead inside" is not a sign of a person who can take a step back and look at a topic from more than one angle.

Of course, they could be right by the luck of the draw but not be bright enough to explain it to me.

In that case, I'm right where I was before, with my experimental evidence which shows that KVL holds just fine in Lewin's circuit.

Heh, maybe I'm right by the luck of the draw. At least I can explain why I think the way I do, and it's because I measured. That's not a bad place to start. :-DD
« Last Edit: November 30, 2021, 08:50:23 am by Jesse Gordon »
 

Offline HuronKing

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Re: #562 – Electroboom!
« Reply #516 on: November 30, 2021, 08:54:17 am »
Quote
The part of this debate I'm involved in has nothing in particular to do with Mehdi. We've been arguing for weeks here about whether KVL holds in Lewin's (and other simple) circuits, regardless of what Mehdi Said he.

Then what I said doesn't apply to you but you seem terribly offended by my having brought it up. Why?

Quote
Literally, yes, but not in context. If you watch the whole video, he's talking about a variety of different cases which he demonstrates - AND - he runs his cases by Dr. Belcher, who writes up a nice writeup about a bunch of Mehdi's experiments, and then concludes that "KVL holds as argued by Mehdi."

So the CONTEXT was that of all the different example circuits that Mehdi gave to Belcher, Belcher said that KVL holds for all of them. Which is what Dr. Belcher said.
And Dr. Belcher even quoted Dr. Feynman.

Srendi has been through your misattributions of Belcher's words. I'm not going to rehash it with you because, again, you want people to chase you in infinite loops. He already said it.
Yes, context matters. Mehdi takes Feynman and Belcher out of context. Mehdi made his positions clear in the first and second videos he released about this. He thinks KVL holds in all cases - he's still saying that. He's wrong.

Quote
Neither Belcher nor Mehdi are saying that KVL holds for every possible circuit of every possible configuration, but rather that it holds for all the ones they've just examined.

By taking Mehdi's words out of context, you make him out to say something completely different than he was actually communicating.

Belcher wouldn't say that because he is an actual physicist who understands Maxwell's Equations. Mehdi on the other hand... this is what he actually is arguing. This is the whole reason he picked a fight with Lewin in the first place.
https://youtu.be/0TTEFF0D8SA?t=51

And in his second video, he still thinks this is true. Now, I should really be clear about one thing - Mehdi thinks he's picking a fight with Lewin but really he picked a fight with physics and won't allow himself to think he could be wrong (he says as much in the EEVBlog podcast).

Quote
Your strong negative bias shines like the sparks off Mehdi's fingertips, and smells like his burning clip leads.

I own a Full-Bridge Rectifier T-shirt and used to be a subscriber. I unsubscribed when Mehdi started preaching pseudoscience.

Quote
And that's what I get far and wide. The people arguing for Lewin being right are dreadfully reluctant to actually show that they can do real physics. See how you side stepped my question?

They claim to know it all, but can demonstrate none of it, except they are sure about one thing, and that is Lewin was right.

I've read through 20+ pages of Sredni and bsfeechannel very patiently pointing to the contradictions in the assumption that KVL must hold all the time, even in the Romer/Lewin circuit. And I read through 50+ pages 2 years ago when Mehdi started this debacle on a large-scale.

Quote
What would you call them? They call us "KVLer's" or "KVL-ALWAYS-HOLD"ers or whatever.

Maxwellians. People like Sredni aren't suggesting that KVL must hold even when it doesn't. It's not one of Maxwell's Equations - it's not sacred. So why the desperation to save it? Why is it so very important that KVL applies to the Lewin/Romer Ring? Well I don't know why. This is why Sredni is fascinated by the cognitive bias - why does everyone want to save KVL so badly?

Quote
I know that air core transformers existed long before Lewin, but I think Lewin was just who really made the party trick well known - the combination of his entertainer style and youtube publicity was what it took to spark it off.

The experiment is an excellent demonstration of the phenomena of non-conservative fields and path dependence. Lewin didn't come up with it nor did he really come up with the interpretations of the physics that describe it. Sredni has cited multiple well-respected authors and texts (it's in Feynman, Purcell, and Romer for starters). I'll add another into the mix: JD Kraus Electromagnetics, Chapters 4-10 and 8-2. Not that this makes an appeal to authority - just that it's not accurate to characterize Lewin's interpretation of KVL and Faraday's Law as the ramblings of a mad MIT scientist crackpot (as much as Lewin fits that stereotype with the wild hair and colorful clothes)... it's actually pretty mainstream in physics and applied EM textbooks.

I'm pretty amazed that just studying Faraday's Law and saying "KVL doesn't always hold" makes one a Lewin cultist. And I'm not even an anti-KVLer... just someone who recognizes the limitations of when you can use it, I guess? To invoke an old joke, does saying that F =/= 0 in a Mechanical Dynamics course mean I don't think F = 0 in a Statics course? F = ma is Newton's 2nd Law... and we have special cases where F = 0. That's all.
 
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Offline thinkfat

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Re: #562 – Electroboom!
« Reply #517 on: November 30, 2021, 09:08:03 am »
Then they posted that textbook page which says that KVL holds if the voltage across the terminals can be unambiguously defined by physical measurements - and by George - we seem to be unambiguously defining the voltages by physical measurements, so I say it's time we all agreed that KVL holds for Lewin's circuit!  :-DD

Except the voltages are not unambiguous:

Not in the circuit above (which is essentially the Lewin ring), not even in the EI core experiment that originally brought you here.
Above, the voltage across "2R" is either "-1/3V" or 2/3V, depending on the path your voltmeter probes are going. That's not what I call "unambiguous".
Everybody likes gadgets. Until they try to make them.
 

Offline Jesse Gordon

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Re: #562 – Electroboom!
« Reply #518 on: November 30, 2021, 09:11:13 am »
Quote from: unknown
All the KVLer's are gone except two, and they are taken down about 12 notches, frantically just repeating themselves

I don't know that anyone's down 12 notches, but I do see a shift.

Quote from: bsfeechannel
Quote from: armandine2
Quote from: bsfeechannel
brilliantly debunked by Lewin.
experimentally?
Yes. Try it yourself.

Ironically, I had tried it myself a year prior with my Lewin Clock: https://youtu.be/nAsZFP8Cfxk

Quote from: bsfeechannel
Lewin showed at least one circuit where KVL doesn't hold. Everyone repeated his experiment and obtained the same result. Conclusion: KVL does NOT ALWAYS hold. End of story.

I repeated his experiment with proper probing and KVL did hold for me -- all the voltages summed to zero.

Quote from: bsfeechannel
He, and everyone who repeated the experiment, measured the voltages and they didn't add up to zero. That's how he showed it.

Yeah, He [Lewin] didn't add up all the voltages, so doh, of course it didn't add up to zero. When I added up all the voltages, then it did sum to zero.

Thinkfat also learned some cool stuff about voltage drop on a shorted winding and a number of other wrong predictions he made.

So yes, I've seen a change, but it's not been in team KVL it's been in team Lewin - and the change I see is their increasing refusal to answer questions which would show the incoherence in their claims.
 

Offline Jesse Gordon

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Re: #562 – Electroboom!
« Reply #519 on: November 30, 2021, 09:23:45 am »
Then they posted that textbook page which says that KVL holds if the voltage across the terminals can be unambiguously defined by physical measurements - and by George - we seem to be unambiguously defining the voltages by physical measurements, so I say it's time we all agreed that KVL holds for Lewin's circuit!  :-DD

Except the voltages are not unambiguous:

Not in the circuit above (which is essentially the Lewin ring), not even in the EI core experiment that originally brought you here.
Above, the voltage across "2R" is either "-1/3V" or 2/3V, depending on the path your voltmeter probes are going. That's not what I call "unambiguous".


AHHH THANK YOU! I've been asking for days what was ambiguous about my reading of the voltage on a toroidal transformer secondary!
The answer? If I don't know how many turns are on the winding, especially if they might change without me knowing it, then the reading is ambiguous.

Ha! Dude!

Even if you take resistors... or batteries... If the number of series resistors or batteries changes without you knowing it, then even the reading of a battery voltage is ambiguous!

In fact, if things which cannot change themselves suddenly must be considered to randomly change themselves, ALL OF PHYSICS FAILS!

And yes, lacing your volt meter lead through the core is adding turns.

Soooo, let's say we have terminals on our transformer secondary windings as shown in the diagram below, and the volt meters are connected WHERE SHOWN, and no volt meter leads are allowed to fall into that hungry transformer core, then there's no ambiguity,  right? Then KVL holds, right?

Remember, we're considering the transformer secondary a lumped element. a black box. No peeking inside. It's got two terminals and that's all we need to know. The voltage BETWEEN THOSE TWO TERMINALS IS UNAMBIGUOUS. That's all that matters. What's going on inside is off limits because it's a lumped element.



Seriously, keep your probes out of the lumped elements!

If you had pure battery and resistor loop, and you were stabbing your probes and random places inside the resistors or batteries, you'd get all sorts of ambiguous readings. That's why we LUMP the elements!
 

Offline thinkfat

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Re: #562 – Electroboom!
« Reply #520 on: November 30, 2021, 10:27:26 am »
Then they posted that textbook page which says that KVL holds if the voltage across the terminals can be unambiguously defined by physical measurements - and by George - we seem to be unambiguously defining the voltages by physical measurements, so I say it's time we all agreed that KVL holds for Lewin's circuit!  :-DD

Except the voltages are not unambiguous:

Not in the circuit above (which is essentially the Lewin ring), not even in the EI core experiment that originally brought you here.
Above, the voltage across "2R" is either "-1/3V" or 2/3V, depending on the path your voltmeter probes are going. That's not what I call "unambiguous".


AHHH THANK YOU! I've been asking for days what was ambiguous about my reading of the voltage on a toroidal transformer secondary!
The answer? If I don't know how many turns are on the winding, especially if they might change without me knowing it, then the reading is ambiguous.
I don't quite know what you're getting at, because I see only single-turn windings, so, would you tell me where you see "transformer secondary" windings in the above diagram?
Everybody likes gadgets. Until they try to make them.
 

Offline bsfeechannelTopic starter

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Re: #562 – Electroboom!
« Reply #521 on: November 30, 2021, 03:53:13 pm »
For whatever its worth Sredni and bsfeechannel, I'm grateful for your efforts to continually educate about this topic even if it really seems like the KVLers are just running in circles through the madness inducing Lewin/Romer loop (puns somewhat intended).

We’re on a mission from God.

 

Offline jesuscf

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Re: #562 – Electroboom!
« Reply #522 on: November 30, 2021, 04:02:31 pm »
The experiment is an excellent demonstration of the phenomena of non-conservative fields and path dependence. Lewin didn't come up with it nor did he really come up with the interpretations of the physics that describe it. Sredni has cited multiple well-respected authors and texts (it's in Feynman, Purcell, and Romer for starters). I'll add another into the mix: JD Kraus Electromagnetics, Chapters 4-10 and 8-2. Not that this makes an appeal to authority - just that it's not accurate to characterize Lewin's interpretation of KVL and Faraday's Law as the ramblings of a mad MIT scientist crackpot (as much as Lewin fits that stereotype with the wild hair and colorful clothes)... it's actually pretty mainstream in physics and applied EM textbooks.

The experiment is an excellent demonstration of Lewin having no idea of what he is talking about!  Do you even understand what 'non-conservative fields' mean in this context?  Have you realized that in the circuit, the one with the wire loop and the two resistors, all the energy induced due to the external varying magnetic field is equal to all the energy consumed by the resistors?  That sounds pretty conservative to me!
Homer: Kids, there's three ways to do things; the right way, the wrong way and the Max Power way!
Bart: Isn't that the wrong way?
Homer: Yeah, but faster!
 

Offline HuronKing

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Re: #562 – Electroboom!
« Reply #523 on: November 30, 2021, 04:28:25 pm »
The experiment is an excellent demonstration of the phenomena of non-conservative fields and path dependence. Lewin didn't come up with it nor did he really come up with the interpretations of the physics that describe it. Sredni has cited multiple well-respected authors and texts (it's in Feynman, Purcell, and Romer for starters). I'll add another into the mix: JD Kraus Electromagnetics, Chapters 4-10 and 8-2. Not that this makes an appeal to authority - just that it's not accurate to characterize Lewin's interpretation of KVL and Faraday's Law as the ramblings of a mad MIT scientist crackpot (as much as Lewin fits that stereotype with the wild hair and colorful clothes)... it's actually pretty mainstream in physics and applied EM textbooks.

The experiment is an excellent demonstration of Lewin having no idea of what he is talking about!  Do you even understand what 'non-conservative fields' mean in this context?  Have you realized that in the circuit, the one with the wire loop and the two resistors, all the energy induced due to the external varying magnetic field is equal to all the energy consumed by the resistors?  That sounds pretty conservative to me!

Oh dear...
https://farside.ph.utexas.edu/teaching/301/lectures/node59.html

Path dependence of the line integral to do work is the defining characteristic of a non-conservative field.
https://courses.lumenlearning.com/suny-osuniversityphysics/chapter/8-2-conservative-and-non-conservative-forces/

We're not even talking about basic electromagnetics anymore (this is in Kraus Chapter 4). Sredni is right - the notches have been lowered back to basic Newtonian mechanics.

Another Lewin stooge apparently (the casual nature of his murdering of Kirchoff is astounding):
http://www.physicsbootcamp.org/Nonconservative-Electric-Field.html

Amazing.
« Last Edit: November 30, 2021, 04:47:11 pm by HuronKing »
 

Offline HuronKing

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Re: #562 – Electroboom!
« Reply #524 on: November 30, 2021, 04:37:02 pm »
More Lewin stoogery I guess - the conspiracy runs deep! This is bigger than the Illuminati:
https://phys.libretexts.org/Bookshelves/Electricity_and_Magnetism/Book%3A_Electricity_and_Magnetism_(Tatum)/09%3A_Magnetic_Potential/9.01%3A_Introduction_to_Magnetic_Potential

"The force on a charge  q  in a magnetic field is  qv×B . This force (the Lorentz force) does not depend only on the position of the particle, but also on its velocity (speed and direction). Thus the force is not conservative. This suggests that perhaps we cannot express the magnetic field merely as the gradient of a scalar potential function – and this is correct; we cannot."

Gawd, they're everywhere!
http://www.sfu.ca/phys/121/1101/lectures/lecture35.pdf

 


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