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Author Topic: Professor Walter Lewin's Non-conservative Fields Experiment  (Read 253074 times)

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It's not as complicated as it may seem...
When I read the Lewin's paper, I remembered a bit more recent paper from Maxim (ics) that I saw some years ago:
http://www.maxim-ic.com/app-notes/index.mvp/id/2238
I had been very impressed by how easy it is to lead wrong measurements!
The Lewin's paper is not original. His point was already emphasized in 1982 by Robert H. Romer in: "What do 'Voltmeters' Measure?" http://ajp.aapt.org/resource/1/ajpias/v50/i12/p1089_s1. Unfortunately pdf not found for free on the web. I had read it after reading the Maxim's paper but unfortunately I have not kept the file. It should be of interest here.

Yes exnihiloets, indeed I've read those papers and more. Most are incorrect in their conclusions, and the authors seem oblivious to the ramifications. There are papers that go back even farther than Romer's, but he seems to be the one that "popularized" the error (and the erroneous, misleading conclusions stemming from it), and ever since then most have simply jumped on his bandwagon.

.99
   

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It's not as complicated as it may seem...
KVL isn't really the issue. The misapplication of physics laws is one of the issues. Another is perspective.

The position sensor example is only one application of this very basic rule. I have individuals working for me who don't really understand something as base as a motor encoder founded upon this example. They all have far more formal civilian education than me. The greatest problem they face is they can't understand that all laws of physics either have examples of where they don't apply or are at risk of being misapplied.

The ramifications of the different meter readings depending upon relative location? I won't hazard a guess. The implications are more than one. The first being that Lewin was correct in everything contained in that lecture. Also the experiment, like all of his experiments covering the lecture, contains every thing emphasized in the lecture.

Beyond that, I'll refrain to avoid effecting any conclusions from .99.

It is incredibly simple.

 

From your first sentence, I see we are in agreement (essentially a repeat of what I said), at least on that. Now we are getting somewhere. ;) It seems now that I have built the apparatus and have actual measurements, now you are starting to change your tune?  ???

If it is "incredibly simple", why has no one here (except myself) yet offered any answers?  C.C  One of the answers is that Lewin's measurements are correct (as he is measuring across the resistors, and not points A and D), but like many other authors, his conclusions are incorrect, and the experiment misleading in general.

.99
« Last Edit: 2011-03-14, 14:11:56 by poynt99 »
   
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OMG -- this discussion is still going! ...the very first SPICE model I made of this problem (results posted) gave results that agree with experimental evidence.
The trick with any simulator is to know how to accurately simulate reality closely enough to be useful... if your simulations are way off then your missing some fundamental understanding. In this case it was easy to get the simulator to yield results that model reality.
   
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When I read the Lewin's paper, I remembered a bit more recent paper from Maxim (ics) that I saw some years ago:
http://www.maxim-ic.com/app-notes/index.mvp/id/2238
I had been very impressed by how easy it is to lead wrong measurements!
The Lewin's paper is not original. His point was already emphasized in 1982 by Robert H. Romer in: "What do 'Voltmeters' Measure?" http://ajp.aapt.org/resource/1/ajpias/v50/i12/p1089_s1. Unfortunately pdf not found for free on the web. I had read it after reading the Maxim's paper but unfortunately I have not kept the file. It should be of interest here.



Here is a link where you can download the Romer paper freely:

EDIT: Sorry Gyula, in this case, due to the numerous possible public viewing of this hot topic, we wish not to have links to copyright material on the forum. If you want this paper, pay for it as I did. Thanks. .99

Here is an extended version of the Maxim Application Note 2238: http://powerelectronics.com/mag/411pet24.pdf  

rgds,  Gyula
« Last Edit: 2011-03-14, 17:19:52 by poynt99 »
   

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.99,
 
I'm not sure what you mean by changing my tune.
As far as I'm concerned, Spice calculates inductance in a length of snapshots instead of di/dt way then fudges the math to make the overall result correct. I just looked at the source code for one used at work. That is indeed how it works.
I have no problem with that. The problem I have is this usage leads to mis or non understanding of what actually happens.

I am looking forward to corrected reasons for this issue. It wouldn't surprise me if you found one.


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"As far as the laws of mathematics refer to reality, they are not certain; as far as they are certain, they do not refer to reality." - Einstein

"What we observe is not nature itself, but nature exposed to our method of questioning." - Werner Heisenberg
   

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It's not as complicated as it may seem...
OMG -- this discussion is still going! ...the very first SPICE model I made of this problem (results posted) gave results that agree with experimental evidence.
The trick with any simulator is to know how to accurately simulate reality closely enough to be useful... if your simulations are way off then your missing some fundamental understanding. In this case it was easy to get the simulator to yield results that model reality.

This discussion is only beginning to reach fruition.  8)

There is absolutely nothing wrong with SPICE in general, nor with my simulation of the Lewin experiment. Please hold off all commentary about SPICE and my simulation of the experiment until you have had a chance to read my full explanation. Otherwise this back and forth nonsense will go on forever. ;) Thanks.

.99
   

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It's not as complicated as it may seem...
I'm going to be preemptive here and close the thread until I am able to present my test data and explanations etc.. In terms of the arguments, there is a deadlock here anyway, so I see this doing more good than harm. If you need to express your thoughts to me anyway, I'd be happy to receive your PM. Thanks for your patience. :)

Guys, this experiment and the debate stemming from it has nothing to do with KVL, nor SPICE.

Hold on to your chairs!  :D

.99
   

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It's not as complicated as it may seem...
Usually, the types that Prof. Lewin mentioned as unable to really understand the basics of Faraday over Kirchoff.

No one is infallible, including our beloved Prof. Lewin. Unfortunately, the good professor Lewin has had an oversight, and come to an erroneous conclusion as a result.

The actual fact is that BOTH Kirchoff AND Faraday are satisfied by Lewin's experiment. (presuming that is what you were referring to)
« Last Edit: 2012-02-19, 09:22:14 by Peterae »
   

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No one is infallible, including our beloved Prof. Lewin. Unfortunately, the good professor Lewin has had an oversight, and come to an erroneous conclusion as a result.

The actual fact is that BOTH Kirchoff AND Faraday are satisfied by Lewin's experiment. (presuming that is what you were referring to)

Unfortunately, I must still disagree. Both are satisfied and Lewin's description is 'almost completely' agreeable for me. It is all about understanding what a meter actually measures and how angle does indeed affect induction and how the common formulas for induction really do not include relative angle. When you include the relative angle it is clear why the meter reads zero directly above and below the coil and why voltage drop from one view is negative and the other view positive.

My point was.... The PMH is only extraordinary because strikes strong interest only in those not understanding basic magnetics - the basics before they were generalized.

There is no current flow unless you magnetize the device with the keeper applied and you don't see more current flow until you remove the keeper. The simple nature of magnetic fields keep the closed magnetic circuit magnetized. It is not much different from preserving the strength of a horse-shoe magnet by applying a keeper bar.

Don't get me wrong... There is a lot to Leedskalnin's work that still interests me. The PMH isn't one, anymore.

 
« Last Edit: 2012-02-19, 09:25:04 by Peterae »


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"As far as the laws of mathematics refer to reality, they are not certain; as far as they are certain, they do not refer to reality." - Einstein

"What we observe is not nature itself, but nature exposed to our method of questioning." - Werner Heisenberg
   

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It's not as complicated as it may seem...
Unfortunately, I must still disagree. Both are satisfied and Lewin's description is 'almost completely' agreeable for me.

How can you disagree with me when you AGREE that both are satisfied?  :D

I must disagree about Lewin's analysis being "almost complete". The oversight results in a completely false conclusion, and this is being touted as the absolute TRUTH (and to make matters worse, it's being taught as such at university level physics).

.99
« Last Edit: 2012-02-19, 09:25:30 by Peterae »
   

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How can you disagree with me when you AGREE that both are satisfied?  :D

I must disagree about Lewin's analysis being "almost complete". The oversight results in a completely false conclusion, and this is being touted as the absolute TRUTH (and to make matters worse, it's being taught as such at university level physics).

.99

Your statement following mine shows the disagreement  ;D

Have you had a chance to actually perform the experiment?

At this date that subject hasn't changed anything. I'm quite sure you and I don't agree on that experiment. I also think this disagreement will not change. So, there is no point in my bringing the subject up, I apologize.

« Last Edit: 2012-02-19, 09:25:55 by Peterae »


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"As far as the laws of mathematics refer to reality, they are not certain; as far as they are certain, they do not refer to reality." - Einstein

"What we observe is not nature itself, but nature exposed to our method of questioning." - Werner Heisenberg
   

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It's not as complicated as it may seem...
Your statement following mine shows the disagreement  ;D

Have you had a chance to actually perform the experiment?

At this date that subject hasn't changed anything. I'm quite sure you and I don't agree on that experiment. I also think this disagreement will not change. So, there is no point in my bringing the subject up, I apologize.

WW,

I doubt that few if any agree with me.

I did perform the experiment, yes. And my findings do not support the commonly accepted conclusions, including your own. The test is scientific enough that there is no requirement to agree or disagree, nor offer opinions. The results are conclusive, and that's what actually counts.
« Last Edit: 2012-02-19, 09:26:23 by Peterae »
   
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@Harvey
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As a side note regarding Poynt99's comment regarding professor Lewin - I disagree wholeheartedly. Professor Lewin did not make a mistake, and he clearly showed that Kirchhoff's Law is a subset and 'special case' of Faraday's law. Any engineer that understands path dependency will fully agree with these statements. Kirchhoff's law simply will not hold where path dependency is present and real world examples of this were previously provided in a prior thread with a link to a well written magazine article on that specific subject.

I would agree with your post 100%, the lengths to which some people are willing to go to conform reminds me of the guy trying to drive a square peg into a round hole which seems kind of fanatical in my opinion.
Quote: "A fanatic is one who can't change his mind and won't change the subject" -- Winston Churchill

Hmm, that quote reminds me of a few of our resident experts, lol.

Regards
AC


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Be careful when you blindly follow the Masses... sometimes the "M" is silent.
   

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I don't know .99 as a fanatic of any kind except the rule of truth.

If he says his results are conclusive then they must be.

 I just can't imagine how any results could overturn those Lewin supplied and have been used since inductive position and direction sensors were invented.


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"As far as the laws of mathematics refer to reality, they are not certain; as far as they are certain, they do not refer to reality." - Einstein

"What we observe is not nature itself, but nature exposed to our method of questioning." - Werner Heisenberg
   
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@Wavewatcher
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I don't know .99 as a fanatic of any kind except the rule of truth.

I would not say .99 is a fanatic either however if he has no proof to substantiate his claim then really he is no better or worse than any other person in this field of technology making "claims", we cannot say one person making an unproven claim is a nut and the other not because that is absurd.

Quote
If he says his results are conclusive then they must be.
They are simply unproven claims until proven otherwise ---- as I said no better no worse.

Quote
I just can't imagine how any results could overturn those Lewin supplied and have been used since inductive position and direction sensors were invented.
You are using the wrong perspective, let's start with a question -- it is well know that many physicists, Nobel Prize winning physicists, disagree on many issues. Now if these experts are supossedly the best of the best and light years ahead of anyone here and always correct or moreso believe they are correct then why do they disagree?. You see someone must be right and someone must be wrong, it does not matter how smart they think we are, their credibility or experience they all have the capacity to be right or wrong. Which kind of put's a new perspective on this I'm an expert so I must be right bullshit doesn't it?, if a Nobel Prize winning physicist can be wrong then all bets are off which is why we require proof, explicit proof which applies in every case and in the proper context.

As well the fact that so many supposedly mature professional people have gotten so upset over contradictions to their opinions should tell us something not about science but people. There is no such thing as objective science when people start dragging their emotions and ego's into the fray, if they are mature and responsible adults then maybe they should start acting like it, as they say ---- prove it. I have always found this comical when some self-proclaimed expert starts ranting and then the name calling starts then personal attacks then attacks on credibility. It is so not professional it boggles the mind, it is more like something we might see from children in a playground yet time and time again we see adults doing this very thing and there is no sense to it.

It should be no suprise that this hubub about Kirchhoff's rule is the same hubub as Betz law which has limitations, not unlike the Earnshaw's theorem hubub or the homopolar generator hubub where almost none of the experts can seem to agree. You see it is not so much about expertise or science but people and of course the quote from my last post ---"A fanatic is one who can't change his mind and won't change the subject" -- Winston Churchill.

Regards
AC



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"Great minds discuss ideas; average minds discuss events; small minds discuss people." - Eleanor Roosevelt.

Be careful when you blindly follow the Masses... sometimes the "M" is silent.
   

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It's not as complicated as it may seem...
As a side note regarding Poynt99's comment regarding professor Lewin - I disagree wholeheartedly. Professor Lewin did not make a mistake, and he clearly showed that Kirchhoff's Law is a subset and 'special case' of Faraday's law. Any engineer that understands path dependency will fully agree with these statements. Kirchhoff's law simply will not hold where path dependency is present and real world examples of this were previously provided in a prior thread with a link to a well written magazine article on that specific subject.

 8)

Just copied this part over from another thread. Applies before Reply #112 above.
   

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It's not as complicated as it may seem...
Harvey,

Right on! on your post about the Lewin experiment. Kirchhoff is satisfied because his laws do not apply. His work was done when Faraday's laws over ruled him. You use the term 'sub-set' and that is completely correct. KVL only applies to path independent potential distribution. Path dependency is the telltale sign.

It is a very good thing this works as Lewin described or there would be dozens of different type devices that would never work.

Sorry .99. I would love to see your conclusive results some time. They must be very convincing.

I came up with almost exactly the same conclusion offered by Lewin a very long time ago. Since then, I've performed variations a couple of times. The conclusions never change.


Just copying this over from another thread. Applies before Reply #113 above.
   

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It's not as complicated as it may seem...
Both are satisfied and Lewin's description is 'almost completely' agreeable for me. [snip] When you include the relative angle it is clear why the meter reads zero directly above and below the coil and why voltage drop from one view is negative and the other view positive.

I would appreciate some clarification/expansion on your above statements WW.

Thanks,
.99
   

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I will be happy to do so. It is a bit late for me right now.

Basically, induction can be calculated to determine the resulting EMF or the resulting current. Both formula are virtually the same.

The difference is one uses the 'apparent' Gaussian surfaces facing each other (two loops parallel to one another = full surfaces facing each other).
The other uses the previous plus the COS and/or Theta or 'the comparative angle' between them.

It has been stated that this angle is already part of common formula for induction. It is but it assumes changing the relative angle only varies the relative surface area. I should say, it assumes the change in relative surface area is the only thing causing a variation of coupling.

When the meter and the loop of wire connecting it to the two points mid to the resistors is directly above or below the coil zero voltage is measured because there induction is cancelled by the opposing two meter branches. If the resistor loop had its own battery then the meter would measure the same all the way around - above, left, below & right.

Since we are only dealing with induction (& path dependent) the meter reading depends upon the path the current takes.
Phase is shifted.
The difference between the two readings (-.1 & +.9) is the expected 1V. A measured potential is the difference between two points not the total readings taken across segments in series - when it is path dependent.

The meter measures what is on the wires connected to the meter - not what is at the other end of the wires. In EM induction the measured values will depend upon the location of the wires/meter of the measuring device because we are dealing with non-conservative fields(path dependent fields).

With such a circuit the most important thing is to look at the difference between measured values. The answer is the same as if KVL is applied to a path independent(conservative) circuit.

KVL is satisfied because it can not be applied to path independent fields. KVL was only meant to be applied to static potentials or snippets of time showing static potentials of conservative fields.

Induced EMF across points in a series loop (secondary of a transformer) may not be added together to match the applied potential. The only way to get the right answer is to find the difference.

Like I said, it is late and I rambled. This isn't even the tough one. I still have problems where we find Faraday's induction is a subset of Lorentz and not always correct (at least, when it is applied where it shouldn't be applied, like KVL - so I'm told  :o )

This is an odd position for me. Here I am.... in defense of accepted theory. Very strange feeling  ;D


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"As far as the laws of mathematics refer to reality, they are not certain; as far as they are certain, they do not refer to reality." - Einstein

"What we observe is not nature itself, but nature exposed to our method of questioning." - Werner Heisenberg
   

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It's not as complicated as it may seem...
When the meter and the loop of wire connecting it to the two points mid to the resistors is directly above or below the coil zero voltage is measured because there induction is cancelled by the opposing two meter branches.
WW,

If I understand you correctly, you are saying that in the depiction attached, there would be zero voltage (or very miniscule) reading on the oscilloscope while "B" is increasing?

Do I also understand correctly that your reason given for this zero voltage reading is because the induced current in each scope wire cancel each other?

.99
   

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I can't say from experience with 6 feet of loop height.

It shouldn't matter. The loop create by the scope leads is the wrong orientation to B to create much induction, in the first place. If there is any measured it would be due to a slightly imperfect vertical orientation and slightly different leg lengths.

If everything is exactly balanced (wire lengths, etc.) you will measure the actual potential difference between the two points(this may be raising a question - I think the proper term for the potential difference is the word 'undefined') - also because induction on that scope loop is cancelled. Making all so well balanced was difficult so I won't be surprised, if anyone does actually perform the experiment, and then cry foul.

I've found the primary coil I used for that and other experiments some years ago. I'm tempted but already know most will claim it is faked.
« Last Edit: 2012-02-22, 01:47:01 by WaveWatcher »


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"As far as the laws of mathematics refer to reality, they are not certain; as far as they are certain, they do not refer to reality." - Einstein

"What we observe is not nature itself, but nature exposed to our method of questioning." - Werner Heisenberg
   

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DC,

There really isn't anything special about what is discussed here. Actually, it is in most higher level books on the subject. I know the contents of these books to be correct. Others say they aren't correct. If this is true and can be proven by experiment, then I want to know.

It is the same old argument. The only thing odd is the participants switched sides  :)

The only time induction is special is when you don't quite understand it.



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"As far as the laws of mathematics refer to reality, they are not certain; as far as they are certain, they do not refer to reality." - Einstein

"What we observe is not nature itself, but nature exposed to our method of questioning." - Werner Heisenberg
   

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It's not as complicated as it may seem...
I can't say from experience with 6 feet of loop height.

It shouldn't matter. The loop create by the scope leads is the wrong orientation to B to create much induction, in the first place. If there is any measured it would be due to a slightly imperfect vertical orientation and slightly different leg lengths.
This is relatively clear; I'll take this as a YES then, agreed?

Quote
If everything is exactly balanced (wire lengths, etc.) you will measure the actual potential difference between the two points(this may be raising a question - I think the proper term for the potential difference is the word 'undefined') - also because induction on that scope loop is cancelled. Making all so well balanced was difficult so I won't be surprised, if anyone does actually perform the experiment, and then cry foul.
This is unclear. What are you trying to say here? It's NOT zero volts?  ???

.99
   
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The increasing B field induces a voltage in the loop such that when integrated equals 1V from A to A or from D to D or anywhere in the complete loop from start to finish the total voltage will be 1V. This is satisfied by Faraday's Law of Induction:


(Image taken from http://en.wikipedia.org/wiki/Faradays_law#Flux_through_a_surface_and_EMF_around_a_loop )

Understanding that the induced voltage of 1V is measured from A to A or from D to D is the first step in comprehending why KVL fails in this instance.

 8)
« Last Edit: 2012-02-22, 06:31:50 by Harvey »
   

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This is relatively clear; I'll take this as a YES then, agreed?

Agreed.

Quote
This is unclear. What are you trying to say here? It's NOT zero volts?  ???

.99

It will not be 'a' voltage measured. IF you are able to measure a voltage the result will vary from -.1 to +.9 on a scope. An analog meter will show zero volts. The effective measurement will be zero or, more correctly identified as 'undefined'. Some measuring devices may show the average between -.1 and +.9 .

Harvey is correct. The only way to measure voltage is both probes on one point. Even then, the placement of meter conductors is crucial and some of the measuring process must be done in one's head to have the final result. In other words, you must place both probes at one point and visualize what the voltage would be if you opened the circuit between the probes.

You don't normally concern yourself with the voltage drop across a component after cutting the component into different length sections. That voltage drop across each section will change with time.


---------------------------
"As far as the laws of mathematics refer to reality, they are not certain; as far as they are certain, they do not refer to reality." - Einstein

"What we observe is not nature itself, but nature exposed to our method of questioning." - Werner Heisenberg
   
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