Discussion in 'Physics' started by MichaelLaMoreaux, Aug 16, 2010.

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1. MichaelLaMoreaux Thread Starter New Member

Aug 16, 2010
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There exists an instance of pseudoscience in mainstream science and education, namely, the understanding of electromagnetic induction. There are two forms of induction. One is responsible for the operation of generators and is called motional emf. The other is responsible for the operation of inductors and is called transformer emf.

Motional EMF is just a direct application of the definition of the magnetic field. This definition states that a charged particle moving in a suitable direction in a magnetic field experiences a magnetic force. The free electrons in a conductor moving in a suitable direction in a magnetic field experience a magnetic force, which constitutes an emf in the conductor, the motional EMF.

When the magnitude of a magnetic field changes with time, it produces an electric field. A closed path suitably oriented in this electric field has an emf, the transformer emf. This closed path may or may not be conductive. The magnitude of the emf is a function of the time rate of change of the magnetic flux linking the closed path. This is given by one of Maxwells classic four laws. This law is sometimes called Faradays Law. This law utilizes a partial derivative, which has the effect of eliminating the effect of motion. The relevant rate of change of the magnetic flux linking the closed path is purely a function of the change of the magnetic field itself and is not a function of any change of flux linking the closed path due to motion of the closed path causing a change of orientation within the magnetic field or changing the size or shape of the closed path.

Between them, motional emf and transformer emf cover all the cases. Now we come to the pseudoscience. There purportedly exists another principle, also called Faradays Law. It is the relevant one of Maxwells Laws with the partial derivative changed to the ordinary derivative, and it only applies to circuits. This version of Faradays Law implies that the rate of change of the flux linking the circuit is the only thing that counts, regardless of the cause. It supposedly includes both motional emf and transformer EMF in circuits. This version of Faradays Law is false! Richard Feynman, in his Lectures on Physics, pointed out that this version of Faradays Law does not always work and gave two examples of this fact, although he called it the flux rule. Motional EMF and transformer emf are independent principles. For them both to be included in a single term of an equation is logically impossible. In every case where the flux change is solely due to motion, the motional emf is the total emf. There is nothing left for the flux change to account for. If the flux change due to motion had an effect, it would add to the motional emf and give twice the value of the actual emf. All flux change is not created equal. Only a changing magnetic field creates an electric field. The changing orientation of a circuit with respect to the magnetic field does not. In most cases of motional emf there is an accompanying flux change. This is a case of correlation, not causation. It is guilt by association. The flux change is just along for the ride. It has no effect. The Faraday disk dynamo is a case where there is no flux change in the circuit, so the flux change and motional emf are effectively separated, and the faulty version of Faradays Law fails completely. The faulty version of Faradays Law specifies no emf, but of course there is one. Virtually every textbook and encyclopedia contains egregious conceptual and factual errors regarding the subject of induction. It would seem that the authors do not understand this part of elementary physics, as simple as it is. It is an indictment of the status quo and a scandal.

Mike

2. studiot AAC Fanatic!

Nov 9, 2007
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Any person who applies a formula in inappropriate circumstances is likely to obtain the wrong answer.

You should always not only state the formula but also the conditions for its validity and ensure that your application falls within the bounds of the latter.

If you do this with simpler versions of Faraday's or Ampere's law then all is well.

3. steveb Senior Member

Jul 3, 2008
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Faraday's Law is a very fundamental law that is true always in the context of classical physics. It applies to electromagnetics even in the regions of severe warping of spacetime sufficient to require general relativity to make predictions. I'll need to check and see if it holds up under quantum field theory, but I suspect it does in some form.

This is a recurring nonsense post that shows up in all the science forums and even in crackpot wikipedia articles. I can't say if the OP is deliberately trying to mislead people, or if he has simply convinced himself that there is some discrepency that has been unresolved, but either way, he is dead wrong in his claim.

Richard Feynman, in his “Lectures on Physics, challenges our thinking in many aspects of physics. He had tremendous insight and his legacy and challenges help people see physics in a new light. There are many paradoxical ideas and misconceptions that come up with regards to Faraday's Laws, and many other laws for that matter. However, there is no credible evidence that Faraday's Law is false. It is as firmly rooted as the law of conservation of charge, or the law of conservation of mass/energy.

There is one aspect to what is said above that I do sympathize with and perhaps this has become a point of confusion for the OP, or maybe he just uses this confusion as a wedge to mislead. Either way, many electromagnetic books do state Faraday's law as having a partial derivative of the magnetic field, rather than the total derivative of the total flux. The latter, which is equivalent to the so called "Flux Rule" is the truly correct version. The one often quoted in books is only valid for stationary surfaces.

One thing that makes this confusing is that it's is not entirely clear how to go from the point version of Faraday's law to the precisely (and i do mean precisely) correct integral version of Faraday's law. The issue is that the blind application of Stoke's theorem yields the special case of stationary surfaces, not the true flux rule. Well, this is what the theorem does, since it does not consider a moving surface. Greater mathematical sophistication is required to do the correct derivation, but that does not invalidate the law itself. In any event, mathematical tricks aside, Faraday's Law is fully verified experimentally and there is no experiment on record that shows it to be false. That should be sufficient for any scientist.

Last edited: Aug 16, 2010

Aug 16, 2010
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steveb,

Mike

5. beenthere Retired Moderator

Apr 20, 2004
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This is an interesting assertion. Perhaps you actually can prove them.

That being the case, there must be some experiment that clearly shows the difference in the two forms of EMF that you claim. Can you share it with us?

6. beenthere Retired Moderator

Apr 20, 2004
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Aha! We have a posting elsewhere - http://www.skepticforum.com/viewtopic.php?f=18&t=13255

And something earlier - http://www.thescienceforum.com/viewtopic.php?p=215387

It might be noted that most of the discussion in the Physicsforums thread is due to inconsistency in terminology. It takes a long time to get most members on the same page.

We might also note that the sensitive experiment that would support the claim of the falsity of Faraday's Law never gets brought out. One member mentions the importance of it, but MichaelLaMoreaux never responds.

7. MichaelLaMoreaux Thread Starter New Member

Aug 16, 2010
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beenthere,

I have already mentioned Faraday's disk dynamo. It effectively separates motional emf from flux change. In this example there is no flux change, but there is motional emf. The emf is entirely accounted for by the motional emf, leaving no room for a contribution from transformer emf, and, of course, there is none. The partial derivative in the one of Maxwell's Laws governing transformer emf is equal to zero because the magnetic flux is constant. The total derivative of the Flux Rule is also zero for the same reason. But the Flux Rule is claimed to include motional emf and yet gives a result of zero, thereby showing it to be false. In this example, there is an emf with no flux change.

There is another case in which there is a flux change through the circuit with no emf. The total flux, however, does not change. Thus, the case satisfies the transformer emf equation, but not the Flux Rule. Imagine a toroidal core wound tightly with a primary winding which is carrying a constant dc current. Wound loosely on top of this winding is a secondary winding. One end of this winding leads to a terminal of a galvanometer. The other end is connected to a slip ring circling the windings. A brush contacts this slip ring. A wire connected to the brush leads to the other terminal of the galvanometer. Now imagine that the secondary winding is smoothly unwound. The magnetic flux through the core is constant, but the flux linking the secondary winding decreases. The transformer emf is zero because there is no change in the magnetic field, itself. The Flux Rule, however, specifies an induced emf due to the flux change through the secondary circuit. There is no motional emf because of the direction of motion of the wire and because most of the magnetic flux external to the primary winding is canceled out due to geometric symmetry.

Mike

8. steveb Senior Member

Jul 3, 2008
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I really don't want to get involved in a pointless debate. Any claims that Faraday's Law is false should be accompanied by a reference to a published paper in an accepted scientific journal. That is how this forum works. Here, we are interested in real science. If I'm wrong, then it will be apparent from any cited references, as well as any follow on verifications from other scientists, which would be easily traceable using the Science Citation Index, or even Google Scholar.

I'll just state that I stand by what I said above.

Also, I'll post a well known analysis by Frank Munley, published in the American Journal of Physics, of the correct analysis of the Faraday disk along with analyses of some of the other confusing arrangements, including the Feynman challenge.

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9. studiot AAC Fanatic!

Nov 9, 2007
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Mike,
If you read post #2, did you agree with it?

10. beenthere Retired Moderator

Apr 20, 2004
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Why do you call it a transformer? A coil carrying DC is simply not going to act like a transformer. All the coil does is concentrate the magnetic field caused by current in the conductor. It is most emphatically not a transformer, despite that extra coil, but a solenoid. You might look again into the behavior of a toroidal solenoid.

Your "secondary" (actually a non-connected coil) is unwound so the moving conductor does not move across a line of magnetic force. Not too surprisingly, it has no current induced. It does not have to be moved smoothly - the motion can be as rapid as may be arranged, and still no induction.

Transformer action comes about with a changing magnetic field. Faraday's Law applies in any condition where the magnetic flux varies over time(some rate of change must be present). Using a solenoid with a stable current would not appear to be a valid way to demo an apparent violation.

Speaking of your "flux change" - where is it? Do you maintain that a wire will have some current induced simply because one end is in a stationary magnetic field and the other end is not? A change in flux, insofar as Faraday's Law is concerned, must be assiciated with a time-varying magnetic field. The change the wire sees of one of intensity, from zero to whatever field intensity the magnet has around it.

11. Ghar Active Member

Mar 8, 2010
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You know I find this uselessly difficult to follow without an actual equation.
Reading descriptions of equations is awful, this forum supports TeX so you can actually write the forms you're discussing.

12. beenthere Retired Moderator

Apr 20, 2004
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If you follow the links in post #6 you will find at least on thread rich with equations. Awfully short on conclusions, though.

Considering that the examples given are no different from several years ago, the thread seems to be plowing very old ground.

I find the discussion in this forum - http://www.skepticforum.com/viewtopic.php?f=18&t=13255 - to be about as illuminating as any.

13. steveb Senior Member

Jul 3, 2008
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This is the correct version of Faraday's Law. You can also call it the flux rule. In this equation, EMF is defined to be the line integral of the electric field (E) around any closed path (or circuit). This is known to be equal to the negative of the time rate of change of flux (phi) , and flux is simply the integral of the magnetic field (B) over any moving or stationary surface bounded by the closed path which defines the EMF. This law was discovered by Faraday. He must have had tremendous intuition to have figured out this very nonintuitive law of nature so early on in the discovery period of electromagnetics. It is ironic that you complain about the lack of a formula (actually, I prefer equations too), because Faraday himself figured out the law, and understood it, and described it without equations. It took Maxwell to generate the proper mathematical statements as you see here. Again, Faraday's insight was incredible.

$EMF=\oint_{\partial S} E \cdot dl=-{{d}\over{dt}}\Biggl(\int_S B \cdot ds\Biggr)=-{{d \Phi}\over{dt}}$

This is the only equation that is relevant here. The OP is telling you that this is a false law even though it is accepted as a true law in the realm of classical physics. I'm telling you that it is a true law. I've provided a reference that refutes his claims about the Faraday disk, and also refutes his claim about Feynman's challenge being a demonstration of a failure of the flux rule. Basically, Feynman's challange is now accepted as a resolved paradox.

When scientists put forth paradoxes and challenges, it does not invalidate a law. What it does is challenge others to double check the law and make sure it is valid. There is nothing wrong with this. It is the OP and not Feynman that is making the claim that the Flux rule is false. He goes around to all the science sites trying to convince people about his misconceptions, yet he can offer no proof of his claims. He accuses others of having no proof, but then offers no proof of his own. He is well aware of the Munley paper, as it is posted in other forums in response to his nonsense. He does not try to show any errors in the Munley analysis, nor can he point to any experiment, or credible scientific paper, that shows Faraday's Law is false.

14. studiot AAC Fanatic!

Nov 9, 2007
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As a matter of interest, Steve, what are you using for your TEX editor?

15. MichaelLaMoreaux Thread Starter New Member

Aug 16, 2010
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As usual, the responses are all over the map. I really believe that my initial post is sufficient for anyone with an ability to understand the subject. I wonder if you respondents have even read it let alone understood it, as you have not really addressed its salient points. Do you really need a paper published in a scientific journal to see the obvious truth of something? Can you not use your own powers of reasoning, or are you just mindless slaves to authority? Is not Richard Feynman, a Nobel laureate, authoritative enough for you. He directly stated that the Flux Rule does not always work and gave two examples. Nothing could be clearer. As to Frank Munley, he should be embarrassed by his paper as should those who reviewed it for him. He conjures up a fictitious flux change from whole cloth in his analysis of the disk dynamo. It should be obvious to anyone that it is a steady state case and that the flux linking the circuit is constant. Is one supposed to believe that the flux linking the circuit just keeps increasing without limit? How can it exceed the total flux of the magnetic field source? What happens after the increasing sector equals the entire disk? Does the dynamo suddenly stop working after one revolution? As to the toroidal transformer setup not being a true transformer, boy, did you miss the point! Who cares if it is a proper transformer? It is not intended to be. The point is that because of the unwinding, the flux in the secondary decreases, even though the flux in the core is constant.

studiot,

As to the conditions of validity, the only restriction is that Faradays Law only applies to a circuit. I am puzzled by the reference to simpler versions of Faradays Law. How much simpler could it get? There is only one term on each side of the equation.

All,

Let us get down to the basics so that we can see exactly where there is disagreement.

1. Do you believe that it is a scientific principle or fact that a magnetic flux linking a circuit which changes solely due to motion of the circuit results in an emf in the circuit solely due to the flux change? I do not.

2. Do you believe that a flux linking a circuit which changes solely due to motion of the circuit produces an electric field? I do not.

3.Do you believe that motional emf and transformer emf are independent? I do.

Mike

16. steveb Senior Member

Jul 3, 2008
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Hi studiot,

I just use the standard text editor we have here. I just type the TeX commands in ascii format directly, using the [tex ] [/tex ] as delimiters.

Steve

17. steveb Senior Member

Jul 3, 2008
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See how you contradict yourself? You ask us to use our own powers of reasoning and not be mindless slaves to authority, then you tell us that Richard Feynman should be authoritative enough for us.

The fact is that we are not mindless slaves, which is why Richard Feynman is not authoritative enough for us. The fact is that this is a challange he raised over 40 years ago. It may have puzzled him then, but it does not puzzle us now. So, in essence, he ended up being wrong, or maybe you just misinterpreted his point. Actually, many of his challenges from his lectures are either wrong or have been misinterpreted. So what? We are all wrong sometimes. Does being a genius, make him infallible? Look at Einstein's involvement with the EPR paradox. He ended up being wrong. However, before he was proved wrong, the paradox sent the quantum scientists into a tailspin, at least until they could come to grips with the issues. Was Einstein any less of a genius because of this? No, the job of the theoretical physicist is to ask such questions and challenge people to think. So, we've thought about it, and Feynman is wrong. Now, it's time for you to move on.

18. beenthere Retired Moderator

Apr 20, 2004
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Rather than go into some further questions, I am simply going to second steveb's motion. Please feel free to find another forum.