Creating a Poleless Magnet Ring

[MS La Moreaux]

Has anyone heard of a permanent magnet in the shape of a ring or toroid with no poles? I believe that one could be made by winding a ring of magnetic material, such as steel, with a wire winding, like one winding of a toroidal transformer. DC current could then be passed through the winding for a sufficient length of time and then the winding removed. One would then have a magnet with no poles, the flux circulating around the ring. I believe that if the ring were uniform and symmetrical, there would be no magnetic field external to the ring. I cannot think of a practical use for such a magnet but just am interested in the principle. Comments?

Mike

 

[Drakkith]

Is this material a hollow torus or a solid?

 

[pallidin]

Remember those old horseshoe shape magnets with a soft iron "keeper" connecting the poles?
There you have it.
Note that there is still some external magnetism, however.

 

[MS La Moreaux]

Drakkith,

I was thinking of solid, but I do not believe that it would make any difference.


pallidin,

Yes, it is similar, but the maximum symmetry of the torus is necessary to eliminate any external field.

Mike

 

[Bob S]

Has anyone heard of a permanent magnet in the shape of a ring or toroid with no poles? I believe that one could be made by winding a ring of magnetic material, such as steel, with a wire winding, like one winding of a toroidal transformer. DC current could then be passed through the winding for a sufficient length of time and then the winding removed. One would then have a magnet with no poles, the flux circulating around the ring. I believe that if the ring were uniform and symmetrical, there would be no magnetic field external to the ring.

B_inside is everywhere parallel to the boundary between air and the magnetic material. If H-tangential is continuous across this boundary, then the tangential B_air = B_inside/μ, where μ is the relative permeability.

I cannot think of a practical use for such a magnet but just am interested in the principle. Comments?

Would there be an Aharanov-Bohm effect

http://en.wikipedia.org/wiki/Aharonov–Bohm_effect

on any charged particle going through the hole in the ring? Is there a practical use?

Bob S

 

[granpa]

Aharonov–Bohm effect:

Schematic of double-slit experiment in which Aharonov–Bohm effect can be observed: electrons pass through two slits, interfering at an observation screen, with the interference pattern shifted when a magnetic field B is turned on in the cylindrical solenoid.

http://en.wikipedia.org/wiki/Aharonov–Bohm_effect

 

[stevenb]

pallidin,

Yes, it is similar, but the maximum symmetry of the torus is necessary to eliminate any external field.

Mike

As pointed out by Bob S, even toroidal symmetry will not eliminate the external field if you only have a permanent magnet.

You could encase the torus in a superconductor to shield the magnetic field, and truly confine it.

A tightly wound toroidal coil with DC current is a cheaper way to have field inside and essentially zero field outside.

... DC current could then be passed through the winding for a sufficient length of time and then the winding removed ...

In other words, don't remove the windings from the ring, and don't turn off the current. Basically, the field from the current will cancel the field from the core, on the outside of the ring. (you can also think of this in terms of the boundary condition mentioned by Bob S, but now include the sheet linear current density K: i.e. Ht1-Ht2=K, which allows Ht2=0 on the outside)

 

[MS La Moreaux]

The lack of an external field is the result of symmetry, not the particular source of the field. The lack of poles implies no external field. If there were an external field, there would be poles. If there is an external field, what does it look like?

Mike

 

[Bob S]

The lack of an external field is the result of symmetry, not the particular source of the field. The lack of poles implies no external field. If there were an external field, there would be poles. If there is an external field, what does it look like?

If there are no surface currents (coils), Curl H is continuous across the boundary between air and the ring (magnetic material), meaning Curl H = 0, or tangential H_air = H_ring.. So B_air = μ₀H_air = B_ring/μ, where μ is the relative permeability of the ring material at field B_ring.

Bob S

 

[MS La Moreaux]

Bob S,

So what does the field look like? What is its shape?

Mike

 

[Phrak]

As pointed out by Bob S, even toroidal symmetry will not eliminate the external field if you only have a permanent magnet.

You could encase the torus in a superconductor to shield the magnetic field, and truly confine it.

Now, that's an interesting proposal. But will the counter-currents in the superconductor, required for cancelation of external fields, also cancel all internal fields?

 

[thehacker3]

http://unitednuclear.com/index.php?main_page=product_info&cPath=70_71&products_id=290

 

[pallidin]

http://unitednuclear.com/index.php?main_page=product_info&cPath=70_71&products_id=290

Most commercial ring magnets actually have the poles on the "flat" sides.
The same is true for the above link, but harder to envision.

 

[thehacker3]

Most commercial ring magnets actually have the poles on the "flat" sides.
The same is true for the above link, but harder to envision.

Well then I'm puzzled by the question - what defines a pole? Like what makes the north pole of a magnet a pole, and not the middle of it?

 

[stevenb]

Now, that's an interesting proposal. But will the counter-currents in the superconductor, required for cancelation of external fields, also cancel all internal fields?

That's an interesting question about an "interesting proposal". Keep in mind that the proposal is not my invention. I've just read discussions on the Aharonov–Bohm effect that talk about using superconductors to remove any doubt that the electron is traveling in a field free region.

I'm not very knowledgeable about superconductor theory so I hesitate to answer definitively. My best guess is that generally the internal fields won't cancel, and that the internal field will always be strengthened. But, I wouldn't be overly surprised if an expert comes here and tells us that it is possible to configure a superconducting shield with a particular core material in a way that cancels both internal and external fields. It seems counter-intuitive to me, but my intuition has failed me often enough that I'm not surprised when it happens.

 

[stevenb]

Well then I'm puzzled by the question - what defines a pole? Like what makes the north pole of a magnet a pole, and not the middle of it?

That's actually a good question. A magnetic "pole" is one of those things that everyone talks about and assumes is straightforward, until they try to define it. I like to think of a pole as the part of a magnet that has the most concentrated field that is typically coming mostly perpendicularly to the surface.

For example, a typical bar magnet or a spherical magnet (like the earth) are like dipoles, and the dipole field pattern (you can look it up in any EM book) has clear poles. Magnetic field lines are always closed, so the north poles field lines circulate back to the south pole.

The OPs example is interesting because there is no clearly identifiable pole, due to the symmetry. The field lines internal to the toroid just circulate back on themselves always. The external field lines also circulate back on themselves.

However, typical ring magnets aren't magnetized in this way. They can be magnetized so that the top and bottom (think heads and tails of a coil-like object) are the north and south poles. Also, they can be magetized so that one side of the circular cross section is the north pole and the oposite side is the south pole. Think about a two dimensional version of the Earth (circle rather than sphere) with a north and south pole.

 

[granpa]

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/toroid.html#c1
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/solenoid.html#c1

 

[MS La Moreaux]

All magnetic field lines of a permanent magnet must pass through the magnetic material, since the iron atoms are the source of the field lines, and therefore the lines must pass through the iron atoms. Any external field lines must therefore pass through the surface of the torus. There is no way for this to happen without violating symmetry. Thus, there can be no external field.

Mike

 

[pallidin]

All magnetic field lines of a permanent magnet must pass through the magnetic material, since the iron atoms are the source of the field lines, and therefore the lines must pass through the iron atoms. Any external field lines must therefore pass through the surface of the torus. There is no way for this to happen without violating symmetry. Thus, there can be no external field.

Mike

Uh... I don't think that's true. Field lines do not have to stay within a material, though a majority will.
For example, take a horseshoe permanent magnet and bridge the north/south poles with a soft iron "keeper''
According to your thoughts, then, there can be no external field.
This is NOT the case.
With that magnet and it's keeper, bring it close, BUT NOT TOUCHING a paper-clip.
The paper-clip WILL be attracted.
Just not as much, by far, if there were no "keeper"

 

[MS La Moreaux]

pallidin,

I did not say that the lines had to stay within the magnetic material; I said that they have to pass through the material. In other words, there cannot be any lines no part of which exist in the material.

Mike

 

[pallidin]

OK, gotcha. We're on the same page of thought.

 

[granpa]

Uh... I don't think that's true. Field lines do not have to stay within a material, though a majority will.
For example, take a horseshoe permanent magnet and bridge the north/south poles with a soft iron "keeper''
According to your thoughts, then, there can be no external field.
This is NOT the case.
With that magnet and it's keeper, bring it close, BUT NOT TOUCHING a paper-clip.
The paper-clip WILL be attracted.
Just not as much, by far, if there were no "keeper"

a horseshoe magnet with a bridge isn't perfectly symmetrical.
A perfectly symmetrical ring magnet with the north south poles aligned along the torus will not and cannot have any external field.

likewise an infinite solenoid will have zero external magnetic field.

 

[MS La Moreaux]

Thank you, pallidin and granpa.

Mike

 

[stevenb]

In other words, there cannot be any lines no part of which exist in the material.

Ah, good point. So, actually, there is no discrepancy with the boundary condition, since there is an effective current sheet running on the surface of the magnet, which allows the boundary condition to be matched, and the external field to be zero.

Sorry, I forgot about that aspect of magnets. The internal dipoles act like tiny little current loops. The internal loops all cancel out, but the outer surface has nothing to cancel it out. (self-inflicted head slap)

 

[MS La Moreaux]

Thank you, stevenb.

I guess we could call it a "stealth magnet."

I have thought of one use for it. It perfects my counter example to Faraday's Law (see Post #51 to my locked thread, "Faraday's Law Is False!," last post March 10, 2010, in this forum). Substitute the toroidal permanent magnet for the core and primary winding.

Mike

 

[granpa]

why no link?

https://www.physicsforums.com/showthread.php?p=2404015#post2404015

 

[MS La Moreaux]

granpa,

Sorry, I did not realize that I could do that. Thanks for providing it.

Mike

 

[stevenb]

I have thought of one use for it. It perfects my counter example to Faraday's Law (see Post #51 to my locked thread, "Faraday's Law Is False!," last post March 10, 2010, in this forum). Substitute the toroidal permanent magnet for the core and primary winding.

Mike

I'm not able to fully comprehend the mechanism, based on your description, but it sounds like you are saying that if you wrap coils around a toroidal core magnet (magnetized in the way you describe), and devise a method to keep electrical connections while you unwind the coils (so that the number of turns encircling the field steadily decreases), there will be no EMF despite the fact that there is a time changing flux.

However, you haven't provided a good reason why there would be no EMF. Motional and transformer EMF are just words used to classify. Whether or not you find that your experiment fits either category is not important. Whether or not others agree or disagree with your classification is unimportant. What is important is that Faraday's law says there will be EMF if flux changes in time, and if there is no EMF as you change encirclements in time, then the law would be invalid in that case.

So, there are two logical questions we are forced to asked here.

1. Have you actually done the experiment and confirmed your notion?

2. If so, why in heaven's name have you not published your amazing result?

Surely you realize such a publication would immortalize your name. Whenever Faraday's name is mentioned in future, your name would logically follow.

Remember that Faraday was an avid experimentalist and believed that experiments are the only source of new scientific discovery. He would never accept any mathematical or logical explanation for a new discovery. Although later history has shown some exceptions with theory driving discoveries, all scientists look to experiments to prove a discovery.

The experiment would need to show that (1) there is no EMF and (2) that the number of encircling loops truly is decreasing. Determining encirclement can be very tricky in some circumstances. Although I don't consider myself an expert, I've done a number of experiments that involve Faraday's Law. If not careful, you can miscalculate encirclements. They can be there when you think they are not there and they may not be there even when you think they are there. I've seen people a lot smarter than I literally pulling there hair out trying to make sense of some arrangements.

In any event, the process is simple. Do the experiment. Clearly show the experimental setup, methods and results. Then let others read a write-up and try to make sense of the result. They will then repeat the experiment to see if they can reproduce the result. If they can't explain why there is no EMF and can't show that the number of wraps is constant, then you are instantly famous.

 

[MS La Moreaux]

stevenb,

No, I have not done the experiment, but it should not be necessary. There are two forms of induction. One is motional emf, which is just a direct application of the definition of a magnetic field. A conductor moves through a magnetic field in such a direction that it cuts the field lines. The free electrons experience magnetic forces on them along the length of the conductor, resulting in an emf. Notice that there is no primary electric field. (There may be a secondary electrostatic field due to the emf, but this is irrelevant.) The other form of induction is transformer emf and is prescribed by one of Maxwell's classic four equations. It states that an intrinsically time varying magnetic field induces a non-electrostatic electric field. A closed path (not necessarily conductive, and suitably oriented) in that electric field will have an emf. These two forms of induction include all the possible cases. They are independent of each other. There is no principle that a change in flux linking a circuit due solely to motion induces an emf in the circuit. Any emf in the circuit due to motion caused flux change is motional emf and not due to the flux change which happens to accompany it. In my counter example, the flux change linking the circuit is solely due to motion. There is no intrinsic change in the flux in the magnet. No electric field is induced. There is no motional emf because the winding is not in the magnetic field. Since induced emf must be either transformer or motional, there is no emf in this case. Faraday's Law supposedly includes both motional and transformer emf. It is not claimed to include anything else. Since Faraday's Law specifies an emf in this case, it is falsified.

Mike

 

[stevenb]

stevenb,

No, I have not done the experiment, but it should not be necessary.

Thank you for answering my first question. Above I explain why I'm of the opinion that it is necessary to do the experiment to prove your point. Keeping it still simpler. You are saying Faraday's Law is wrong because another law (or set of rules), which logically can not be Faraday's Law, gives a different answer. How do you choose between two theories, that each give different answers, except by experiment? You are obviously giving greater credence to the other law, but how do you convince someone else who believes that Faraday's Law is a more fundamental law?

I guess I'll rephrase my second question, since I originally made it contingent on whether you had done the experiment.

2. Since you are confident that you can disprove Faraday's Law and have not done the experiment, why wouldn't you next do this relatively simple experiment, publish the results and get the credit for a great discovery? Or, perhaps that is your plan?

 

[stevenb]

No, I have not done the experiment, but it should not be necessary.

I should also point out that there is another aspect to this question. In addition to doing the experiment, you also need to show your application of Faraday's Law and demonstrate that threre is a discrepency between the law and the experiment.

I've been rereading your description of the experiment, and I now think I understand your setup. Now that I understand it, I actually agree with you that there will be no EMF, but this still does not invalidate Faraday's Law. When I apply Faraday's law to the problem, I get EMF=0. In effect, as counterintuitive as this will sound, there is no change in number of encirclements, and hence no time changing flux.

In order to see the error in your logic, I would propose a slight modification to your experiment. Instead of using a slip-ring and brush, let a long length of wire run by the brush (in contact) as you pull the wire through. From this viewpoint, you can see that you will never unwind the coil. The coil stays on the toroid with the same number of turns, provided you have a very long length of wire to keep feeding into the stream. The slip ring example is analyzed from the same point of view. As the ring spins, it traces out additional loops.

Having read some of your other posts, I know you don't accept this type of explanation, but this is the correct way to apply Faraday's Law. In order to provide you another viewpoint, consider how your arrangement with the slip ring would decrease the number of encirclements. Since the number must be an integer, how do you gradually go from 100 to 99 to 98 turns etc.? In other words, if you have 100 turns and the length of the circumference of one turn is 1 cm, and you pull the wire by 0.1 cm, you can't say that you've encircled the field by 99.9 turns.

Anyway, I know you won't accept this, so let's just agree to disagree on this. The bigger issue here is not whether you are right or wrong. I think you actually have provided a very interesting thought experiment, that is worthy of thinking about. The main point here is that it's ok to challenge a law with a thought experiment, but you should not make the claim that a firmly established law is invalid without following a reasonable scientific approach. You need to carefully explain the experiment, carefully do an analysis, carefully do an experiment, and then (most importantly) allow others to examine all of this, they/we can then reproduce your experiment, check your analysis and validate your idea. That's how the scientific process works.

 

[MS La Moreaux]

stevenb,

The two principles upon which Faraday’s Law is supposed to be based, namely motional emf and transformer emf, are principles of nature. Faraday’ s Law is not based upon any principle. It does include transformer emf, but its apparent inclusion of motional emf is just a mathematical or geometrical coincidence. Faraday’s Law is just a numerical equality, not a mathematical description of a principle, and the numerical equality does not even always hold true. The Lorentz equation does what Faraday’s Law only claims to do (and the latter only for circuits). It includes both transformer and motional emf and does it properly by the sum of separate terms. Faraday’s Law tries to cram them both into a single term, which is logically impossible because they are independent.

Your idea that the number of turns has to be an integer is not true. Without the device of the slip ring there has to be an integral number of turns, but with the slip ring the flux linking the winding gradually and smoothly decreases as the coil is unwound. I do not see how there could be any confusion concerning encirclements. When the coil is fully unwound there will be no more flux linkage. (The slip ring always has its own constant flux linkage, but it is a separate circuit. Its spinning has no effect.)

I independently determined that Faraday’s Law is false, but it was know to be the case way before that. Richard Feynman pointed it out. A physics professor recently told me that above the undergraduate level, the matter is made clear, but that Faraday’s Law is an oversimplification for undergraduate students. My view is that if simplification is desired, Faraday’s Law should just be eliminated. It would not be missed since it is redundant.

Mike

 

[stevenb]

A physics professor recently told me ...

Feel free to mention the name of the Prof and the school he teaches at. Can you give the reference to the grad level textbooks which you/he are talking about?

above the undergraduate level, the matter is made clear, but that Faraday’s Law is an oversimplification for undergraduate students.

I have noted just the opposite of what you said. My undergrad text on EM theory simplifies the presentation of Faraday's Law, while my three grad level texts show Faraday's law as one of the four Maxwell Equations. I'm tempted to quote them all, but I know you will still not be convinced. So for the benefit of others, I'll just mention Jackson, which is well respected here. I'm on my cell phone now, so later I'll paste in the page and equation number.

 

[MS La Moreaux]

stevenb,

His name is Professor Keith Riles of the Physics Department of the University of Michigan at Ann Arbor. I do not know the titles of the textbooks to which he referred. I do not believe that he is aware of the lack of widespread awareness of the situation. I am aware that many textbooks call that one of Maxwell's Laws Faraday's Law, which only adds to the confusion surrounding induction. Professor Riles does the same, as did Richard Feynman. The version we have been discussing in this thread is just that one with the partial derivative changed to the total derivative, which is obviously suspect on the face of it. Actually, it makes sense to call that one of Maxwell's Laws Faraday's Law, since the other version is false.

Mike

 

[MS La Moreaux]

stevenb,

I found an email sent to me by Professor Riles. Here is part of it:


"My own approach to teaching Faraday's Law depends on the
level of the class. In elementary courses for premeds and
engineers, I always point out that the EMF in moving
circuits can be derived from motional EMF while presenting
the traditional "Faraday's Law" approach at the same time,
but I don't draw special attention to the mathematical
machinery that allows both approaches to give the same
answer. When I teach honors physics majors at the elementary
level or teach upper level or graduate E&M courses, I do
draw attention to the "trick" that allows Faraday's Law to
give the right answer even when, strictly speaking, it
doesn't apply.

"The nation's most popular textbook for junior/senior E&M courses
for physics majors is David Griffiths' "Introduction to
Electrodynamics". On page 303 (3rd edition) he does explicitly
draw attention to the different mechanisms and states that
he does not regard a loop of wire drawn through an inhomogenous
B field to be an instance of Faraday's Law. Griffiths notes that
this "peculiar accident" of mathematical agreement led Einstein to
special relativity.

"I also checked the text I used as an undergraduate (Reitz, Milford
& Christy, "Foundations of Electromagnetic Theory", 3rd edition).
It too drew attention to the different phenomena involved in
what is loosely called Faraday's Law.

"So I think most physicists do receive the education you would like
them to receive on these subtleties. It's when the subject is
taught at the elementary level that the treatment is typically
superficial. Although I realize that bothers you, it may help to
realize that there is a great deal of pedagogical oversimplification
in those elementary courses. For example, we usually simplify the
presentation of angular momentum and moment of inertia as if
rotations occur about a single axis. We don't present relativistic
transformations of E and B fields or the notion of "retarded time".
At most we only touch upon the magnetic vector potental, and so on."

Mike

 

[stevenb]

The version we have been discussing in this thread is just that one with the partial derivative changed to the total derivative, which is obviously suspect on the face of it. Actually, it makes sense to call that one of Maxwell's Laws Faraday's Law, since the other version is false.... but that Faraday’s Law is an oversimplification for undergraduate students. My view is that if simplification is desired, Faraday’s Law should just be eliminated.

Mike

Unfortunately, what you are putting forth here is complete total and utter misinformation. I don't expect anyone to just take my word for it, but I refer to Jackson section 6.1 for this. In this section Jackson talks about Faraday's Observations, and clearly shows that the mathematical expression of Faraday's Law is with the time derivative on the outside. These are equations 6.1, 6.2 and 6.3. These equations are then restated in summary form as equation 6.4.

Jackson then talks about special relativity (with obvious implied reference to Lorentz invariance). He then goes on to examine the consequences of Galilean invariance. Note that Galilean invariance is an approximation. Maxwell's equations, in correct form, are Lorentz invariant, not Galilean invariant. However, at speeds much less than the speed of light the equations valid under Galilean invariance are useful, even if approximate.

You have spread so much misinformation that I'm forced to post the exact pages I'm referring to. There it is in black and white in a "Graduate Level Text" in the most respected book on electromagnetic fields.

Since, I can only attach 3 pages, I'll follow this post with the last page.

 

[stevenb]

And the final page, with the most important quote "Faraday's law is no approximation".

Study this carefully and get off your kick to try and disprove Faraday's Law. It does nothing but spread misinformation.

 

[MS La Moreaux]

stevenb,

Thank you so much for posting the links to the pages from Jackson. They are perfect for succinctly presenting the mainstream view. You are right on two counts. Jackson backs you up, and I disagree with Jackson.

Let us consider a few claims made by Jackson:

1. On the second page, equation 6.4 refers to circuit C. It is stated that “The circuit C can be though of as any closed geometrical path in space not necessarily coincident with an electric circuit”. This means that if there exists a static magnetic field in space, and one imagines a closed path in the shape of a circle in that field, and one mentally rotates that closed path about one of its diameters, that this mental activity will induce a real emf in that closed path! Pretty neat!

2. In equation 6.4, Faraday’s Law has the total derivative. In equation 6.11 on the fourth page, it has the partial derivative. Thus, Jackson seems to be stating that both forms are equivalent. But the partial derivative eliminates any effect of motion, while the total derivative includes the effects of motion. One includes motional emf while the other does not.

3. There is no electric field associated with v x B. The curl of v x B is therefore always zero. Thus, the second term on the righthand side of the last equation on the third page is always zero, which invalidates equation 6.5.

It seems as though Jackson does not really understand induction. He seems to have a lot of company.

Mike

 

[stevenb]

It seems as though Jackson does not really understand induction. He seems to have a lot of company.

I think induction is a very tricky topic to understand in its deepest levels, but you still have provided no proof that Faraday's Law is invalid. Feynman also provided no proof. All of his objections were answered in the attached well-known paper by Scanlon et. al. (and yes I know you would be counting them with Jackson, since the approach is the same), and there is the much later Munley paper that you also have an objection with.

This forum requires references from established textbooks and refereed journals. You have provided no such references. You keep harping back on the challenges Feynman brought up in the 1960's even though the Scanlon paper addressed those examples, not too long after that. You can offer no proof of your claims in line with the rules of the forum, and you also refuse to do any experiments, or offer any analysis of your own, or try to publish what you claim is your own discovery that invalidates Faraday's Law.

If you are going to accuse Jackson, Scanlon, Henriksen, Allen and Munley of not understanding induction, maybe you should first explain to us how you can have a closed path that encircles a magnetic field line a fractional number of times. Please attach a drawing and educate us.

The bottom line is that your explanations make it clear that you really don't know how to make a proper closed path and surface that is valid for applying Faraday's Law. If you would focus on learning the proper way to do this, you would find that most of your objections go away. Even then, Faraday's Law will be a little confusing to you, and the rest of us, because it is inherently a non-intuitive law that is challenging to think about in some contexts. But, our difficulties should not be taken as evidence that the Law is invalid.

Should you ever find a real violation of Faraday's Law, again I say "by all means publish it". Then it will be a reasonable topic for us to talk about in a forum like this. Why do you spend so much time trying to convince people in forums with unfounded statements, rather than publishing meaningful science in the accepted journals that would lend credence to your claims? This makes no sense to me.

 

[MS La Moreaux]

stevenb,

Thank you for providing the link to the Scanlon paper. His analysis of the homopolar generator suffers from the same flaw as Munley’s. It should be obvious that the magnetic field linking the circuit does not vary with time. It is a steady state case. What happens after a complete revolution? Does the linkage just keep increasing without limit, beyond the total flux of the source? The entire analysis is spurious.

The analysis in the main part of the paper is implicitly restricted to that particular type of case, involving a wire circuit moving through a magnetic field or sitting in a changing magnetic field. Faraday’s Law is not supposed to be limited to such cases.

As to fractional turns, consider a linear solenoid. Turns are being removed at one end by unwrapping the wire around the stationary core. As a turn is being removed, the wire crosses through the flux so that the fraction of the flux linked to the circuit is gradually decreased. This, of course, cannot be done with a toroidal electromagnet because the wire has to be threaded through the hole in the torus. With the device of the slip ring, however, the effect is similar. The circuit is completed from the end of the winding through both sides of the slip ring to the brush. As the winding is unwound, the proportion of the flux linked by each side of the slip ring changes gradually until another whole turn is completed and the slip ring momentarily is not part of the circuit.

I did not set out to overthrow Faraday’s Law. I noticed logical errors in my textbooks. After studying the situation long and hard and checking out other sources, I came to the conclusion that Faraday’s Law is false. There are multiple reasons that all lead to this conclusion. No one has been able to refute any of my points, and few have tried. They abuse my motives, denigrate my credentials and repeatedly recite references that they can parrot wonderfully but do not seem to understand. They profess their complete faith in Faraday’s Law and do not seem willing to question it, even in the face of simple, reasonable, straightforward, logical challenges to it.

You claim that motional and transformer emf are just terms used to classify. I believe that each is the result of recognized and independent principles and that it is equally recognized that together they explain every case of induction. You challenge me to perform an experiment that proves my case. My counter example clearly distinguishes between flux change solely due to motion and motional emf. Can you provide references to any experiments that demonstrate that flux change due to motion produces an emf that cannot be attributed to motional emf? It seems to me that Faraday’s Law has not been demonstrated to be true in every type of case. It has not been shown that Faraday’s Law exactly encompasses motional and transformer emf, neither more nor less. It seems that the textbook authors have been copying from one to another for generations without realizing that what they claim has not been and cannot be established. If the reviewers do not understand the subject, what is the use of submitting a paper to be reviewed?

I would really like to find out exactly on what we agree and disagree. If we could establish a common ground from which to argue, I believe that it would be enlightening.

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

Do you believe that a solely motion-caused change in a flux linking a circuit produces an electric field? I do not.

Do you believe that a solely motion-caused change in a flux linking a circuit produces an emf solely due to the flux change? I do not.

Do you believe that a motion-caused change in a flux linking a nonconductive closed path results in an emf? I do not.

Mike

 

[pallidin]

Well, nothing is "God speak" to be sure.
Have you performed ANY, actual experiment that validates your position?

 

[MS La Moreaux]

pallidin,

No, I have not.

Mike

 

[pallidin]

OK, what I would recommend is that you design and execute an experiment that supports your theory.
Give it much thought... these things are not easy.

 

[MS La Moreaux]

palliidin,

I appreciate the encouragement, but I will not be doing any experiments. I do not see that they are necessary. I believe that analysis of what has already been done and its explanation is all that is required. I know that everything published by "experts" is not correct because they disagree with each other, and other statements just defy logic. I believe that the subject is basically simple, but that mathematics, while necessary, obfuscates the subject. The underlying principles seem to get lost in the exercise. Math is not physics, so that math that is perfectly good in its own right is misapplied to the physical situation. Then, to justify incorrect results, tortured reasoning is used.

Mike

 

[stevenb]

Thank you for providing the link to the Scanlon paper. His analysis of the homopolar generator suffers from the same flaw as Munley’s. It should be obvious that the magnetic field linking the circuit does not vary with time.

You are very welcome. You are partially correct in that his analysis is basically the same. I see no flaw in the analysis myself (I don't see any of the other flaws you mentioned previously either, but I don't see the point of arguing all these points). It should be obvious that his chosen closed path does see a flux change. Your path does not, but you are not using the correct path. He explains this clearly, but you decide to reject it. That is your right, but you are basically choosing to be wrong. This might come across as arrogant, but I mean this from a logical point of view. You chose a method that gives the wrong answer. Everyone else chooses a method that always gives the right answer, based on experimental verification. We call the method that always gives the right answer Faraday's Law. Guess why. Because it mathematically gives the results that agree with Faraday's observations, so we do him the honor. But, you say, "No, don't do it that way. Do it my way. Oh, and when you do it my way, you get the wrong answer, therefore Faraday's Law is wrong". That's basically what you are doing whether you can see it or not. Or, maybe you think you are doing it Feynman's way. Well, his way was wrong. Question, did you ever see Feynman publish a rebuttal paper to the Scanlon paper? Or, was the conspiracy so large as to silence him as well?

What happens after a complete revolution? Does the linkage just keep increasing without limit, beyond the total flux of the source? The entire analysis is spurious.

This is a perfect example of one of your many misconceptions. No offense intended here, I mean this as constructive criticism. Yes, the flux does keep increasing without limit for the chosen path. The point you are missing is that these chosen paths, and their associated fluxes, are arbitrary. The flux change, and not the flux value is the physically meaningful entity. Remember that Faraday's law works for any and all closed paths (i.e. as prescribed). You are free to choose, but some are easier to analyze than others, so pick the easy one. However, and this is the important point, once you choose, you can't abandon that contour and choose another. Stick to the chosen contour (by the given rules which are required by basic physical principles), no matter what it does.

You make the same mistake in your toroid thought experiment. You assume because you can consider the unwound coil as having no wraps, while the starting arrangement has (let's say) 100 wraps, that flux must change. But I can choose a contour for the unwound coil that has 1 million encirclements by going 1 million times around your slip ring. Once I choose this contour, I can reverse to rotation and rewind the physical coil with 100 wire wraps, but my chosen contour still has 1 million wraps. That's what Faraday's law demands. If you don't do this then you are not applying Faraday's law. The number of coil wraps is not generally the same as the number of encirclements used in Faraday's Law. In simple cases it often is, but there is no requirement in general. It's that simple.

As to fractional turns, consider a linear solenoid. Turns are being removed at one end by unwrapping the wire around the stationary core. As a turn is being removed, the wire crosses through the flux so that the fraction of the flux linked to the circuit is gradually decreased.

Correct!

This, of course, cannot be done with a toroidal electromagnet because the wire has to be threaded through the hole in the torus.

Correct!

With the device of the slip ring, however, the effect is similar. The circuit is completed from the end of the winding through both sides of the slip ring to the brush. As the winding is unwound, the proportion of the flux linked by each side of the slip ring changes gradually until another whole turn is completed and the slip ring momentarily is not part of the circuit.

Sorry friend, but you are completely wrong here. Remember I asked you to attach a drawing? If you draw it out, you will see your error. What you are describing is not possible. If you do not cross through the flux by cutting the toroid, you can not decrease the number of turns fractionally. Draw it out please. This is too trivial a thing to even be discussing.

If you can't get past this simple part, there is no point for me to go on. If you can at least acknowledge this fact, then I would be willing to go on to your other questions and carry the discussion further. I don't mean that in a rude way, but honestly, if we can't agree on this simple topological point, there is no chance for us to find common ground. If you can't acknowledge this point, then I'm perfectly happy to leave the thread as is because there is no chance for any serious person to be misinformed by your ideas. They will see the unwillingness to face simple logic right here. And, if there are any that don't see it, well they don't have much chance of learning this anyway, and no harm is done.

Bottom line, ... if you wrap a closed contour path around a closed magnetic flux line, you must do this an integer number of times. Like I said, draw me a counter example. Draw an example with 2.25 turns, just to keep it simple. Maybe if I see how you are visualizing it, we can get to the bottom of the confusion.

By the way, you go into many questions on what you and i believe. What we believe is irrelevant. Science has a process and the process has been followed and continues to be followed. I personally see no flaws in the current acceptance of Faraday's Law, but I see a great number of flaws in your ideas. Obviously, you will say just the reverse, so I guess I can't blame you for sticking to your guns. However, I do blame you for not following the scientific method here, but I've already said enough on that point. You are free to either accept this criticism or not.

and repeatedly recite references that they can parrot wonderfully but do not seem to understand. They profess their complete faith in Faraday’s Law and do not seem willing to question it, even in the face of simple, reasonable, straightforward, logical challenges to it.

Don't think that I have not given this topic considerable thought. I've studied EM theory for 25 years, taken 2 undergrad classes, 2 grad level classes, about 10 other grad level classes that use EM theory. Then after school, studied it as a hobby and use it my profession as an electrical engineer. I did an experiment on Faraday's Law as part of engineering research that was published just last month. I still consider myself an amateur when it comes to EM fields, and still continue to study and apply it, but I know enough to follow any of the papers and texts that have come up here. They are logically sound and consistent from both a mathematical and experimental point of view. This doesn't mean that Faraday's Law is not open to question, but it means that it takes more than your words, without experiment and analysis or solid logical foundation, to question it.

I recall reading your words at another forum, that you don't even understand special relativity. Have you considered the possibility that instead of the entire world being wrong, that maybe you are the one with the improper foundation to make full sense of this subject?

 

[stevenb]

Like I said, draw me a counter example. Draw an example with 2.25 turns, just to keep it simple. Maybe if I see how you are visualizing it, we can get to the bottom of the confusion.

So, I thought that I should post a drawing if I'm going to ask you to post a drawing. In my attached example, I show a closed contour (dotted red line) which will have an attached surface that must cut through the toroid's internal field 2 times. The drawing shows 4 views with one quarter turns of the slip ring. A voltmeter is shown (note that the voltmeter's resistance closes the path, you can implement the voltmeter by any means, or just short the path if it bothers you) with an attached conductive wire (solid black line) that attaches to a conductive brush. The brush always contacts the conductive slip ring which is attached (at the black dot) to a wire which initially wraps the toroid twice. As the wire is pulled, the slip ring turns, and the wire unwinds. The red dotted line shows a contour path that can be used with Faraday's law. I could choose another contour, but I decide on this one because I find it simplest to think about it.

As I asked, can you draw a similar example with the contour encircling the toroid 2.25 times (or choose any fractional value you like) at any point in time?

 

[MS La Moreaux]

stevenb,

Wow! What spectacular drawings. I have no idea how to do that. I certainly do appreciate the trouble you have gone to in providing them.

Congratulations! You got me! (Appropriate head slap here.) Before seeing your images, after further reflection, I came to the conclusion that my counter example is flawed, but for a different reason than you give. In my analysis the flux decreases to zero in steps, one for each turn of the winding. But in between, the circuit would split into two paths around the slip ring and then reconnect, providing a smooth decrease in the flux. The two paths, of course, are not addressed by Faraday’s Law. I would post a correction to my original thread, but it is locked.

I must say that I do not understand the use of the contour. I would think that it would have to be the circuit. If it is not the circuit, then how is it related to reality? What is the meaning of the emf if the emf is not that of the circuit? This seems to be one of those many areas of confusion surrounding Faraday’s Law. Is there supposed to be an emf around the contour in a case of pure motional emf where the contour is not a circuit?

I apologize for my slow responses, which may get even slower. I have a busy schedule ahead.

Mike

 

[MS La Moreaux]

The idea of the contour circling the slip ring one or more times makes no sense. The slip ring is a single-turn winding, and traversing it one complete time or more does not constitute a closed path in the sense of Faraday's Law.

Returning to Scanlon's analysis of Faraday's disk generator, he assumes a uniform magnetic field over the disk. In the version Richard Feynman addressed, this was not the case. A bar magnet was positioned near one portion of the disk. Thus, according to Scanlon's analysis, there would be a pulsing emf as the contour passed by the magnet. This is not what actually happens; the emf is constant.

To make my objection to Faraday's Law clear, let us examine a typical wire-wound generator. The emf is motional. The wire of the armature winding cuts the magnetic field lines, resulting in magnetic forces on the free electrons in the wire, constituting an emf. This emf is numerically equal to minus the time rate of change of the magnetic flux linking the winding, but it is not the result of that changing flux. The motional emf and the flux change are mathematically dependent, but physically independent. Therefore, the changing flux linkage has no effect. Faraday's Law does not explicitly state, but implies, and it seems to be widely believed, that the flux change produces the emf. The mathematical equality between the flux change and the emf in this example was derived only for this type of case and only holds for this type of case, not for every case.

Mike

 

[stevenb]

The idea of the contour circling the slip ring one or more times makes no sense. The slip ring is a single-turn winding, and traversing it one complete time or more does not constitute a closed path in the sense of Faraday's Law.

I believe it does make sense and it does constitute a closed path as allowed by Faraday's Law. Again, you are not free to make up your own rules. If you make your own rules, all you do is disprove Moreaux's Law and not Faraday's Law. You will get no argument from me that Moreaux's law, and his general approach to science, are flawed.

However, there is no requirement to use the multiple encirclements contour, if it bothers you. You are free to create a mathematical contour that instantaneously changes the number of loops by integer steps. However, applying Faraday's law at the time that you switch contours becomes tricky mathematically. If you instantaneously change the contour abruptly, then the integrated flux changes instantaneously and the time derivative goes to infinity. Thus, Faraday's law shows no EMF as the ring spins, and at the instant of switching contours, the calculation is undefined. So, you can't say what the EMF is at that instant.

But, now someone else comes along and uses the same approach, but changes the path just slightly so that his contour switch happens 1 picosecond later. Now he finds the EMF is zero for all times, except he doesn't know the answer for the (different) time of his contour switch. Then you both compare notes and realize that EMF must be zero always.

Returning to Scanlon's analysis of Faraday's disk generator, he assumes a uniform magnetic field over the disk. In the version Richard Feynman addressed, this was not the case. A bar magnet was positioned near one portion of the disk. Thus, according to Scanlon's analysis, there would be a pulsing emf as the contour passed by the magnet. This is not what actually happens; the emf is constant.

You amaze me with the words "according to Scanlon's analysis". You are describing a different problem which they didn't solve, so you can't say what their analysis would be for your example. I'm also amazed that you have not presented your own analysis, yet you claim to know the answer that Faraday's Law will give. This is not a trivial problem to solve, and Munley discusses some of the issues here such as the non-conservative nature of the field which results in EMF that is path dependent. So it's not clear how Faraday's Law relates to a meter measurement. I'd have to think on this long and hard before I could make any definitive statements here. I'd love to see your solution, then I could make a judgement. Until then, your objection is just a wild claim with no support. Indeed, you have claimed both the mathematical solution and the experimental result with no support.

If you want to overturn Faraday's Law, the burden in on you to prove both statements.

1. Faraday's Law predicts pulsing EMF to an observer in a particular reference frame.

2. Experiment shows constant EMF for the same observer and reference frame.

One or both of your statements may, in fact, be true, but just stating them doesn't make it so, and you can't expect the rest of the world to accept your statements on faith. You have been given considerable license by the moderator here to present your views. You say you don't want to publish because the "establishment" will reject your ideas, but you don't even take advantage of this venue. Where is your proof? Let's see it.

To make my objection to Faraday's Law clear, let us examine a typical wire-wound generator. The emf is motional. The wire of the armature winding cuts the magnetic field lines, resulting in magnetic forces on the free electrons in the wire, constituting an emf. This emf is numerically equal to minus the time rate of change of the magnetic flux linking the winding, but it is not the result of that changing flux. The motional emf and the flux change are mathematically dependent, but physically independent. Therefore, the changing flux linkage has no effect.

I'm not sure what you are getting at here. I think I agree so far (remember that what you and I agree on is irrelevant because we could both be wrong), but so what? Maxwell's equations are not really cause and effect relationships because electric field and magnetic field are just components of the electromagnetic field tensor. They are related, but it is incorrect to say that changing magnetic field causes electric field, or that changing electric field causes magnetic fields. This is another reason why your lack of training in special relativity is a big problem. Without an understanding of the covariant nature of the electromagnetic field tensor in vacuum, as well as an appreciation of the reference frame issues that come up with fields in media, you are at a serious disadvantage. Scanlon et. al. discuss this issue and point out that a circuit with moving media is akin to a fluid, and this brings in reference frame complications. This is tricky stuff to to get right, but again I point out that our personal difficulties are not evidence that the law has exceptions. One must think carefully and apply all relevant known scientific principles. Some of these principles were not fully understood until long after Faraday's and Maxwell's publications. Still, Faraday is not the one who tried to formulate a mathematical formula, and indeed he was highly suspect of attempts to do this. Faraday's observations and intuitive description of the Law still hold up today.

Faraday's Law does not explicitly state, but implies, and it seems to be widely believed, that the flux change produces the emf.

You are correct that the law does not STATE that. As to what it IMPLIES, that is more debatable, but I'm willing to agree (for the sake of argument) that the implication is there in the vector form of Maxwell's equations. A proper tensorial representation would not have this implication. Still, this is all irrelevant to the validity of Faraday's Law. It either predicts correctly, or it does not. So far, you have not provided convincing evidence that the Law fails to predict. I'm open to consider your evidence, but so far I've seen nothing that looks like a serious analysis or any attempt whatsoever at an experiment.

The mathematical equality between the flux change and the emf in this example was derived only for this type of case and only holds for this type of case, not for every case.

This is an unfounded statement. I believe it is incorrect, but I'm open to see the evidence you have as to it's correctness. However, the first part of this is still irrelevant to the validity of the law. Even a law that is a wild guess might ultimately hold up to scientific scrutiny.

Again, you have not provided anything that even hints at proof that Faraday's Law is invalid. So far, it is alive and well, ... retired and taking a snooze at a beach in Florida. I have yet to meet an immortal law of nature, so perhaps its days are numbered and perhaps you are its "Grim Reaper". Do you have an axe? Do you have the strength to wield it?

 

[pallidin]

Again, you have not provided anything that even hints at proof that Faraday's Law is invalid. So far, it is alive and well, ... retired and taking a snooze at a beach in Florida. I have yet to meet an immortal law of nature, so perhaps its days are numbered and perhaps you are its "Grim Reaper". Do you have an axe? Do you have the strength to wield it?

Ah... I like Florida.
Still, the question stands intoned by steven; what EVIDENCE disputes Faraday's laws?
Not meaning YOUR evidence, rather, evidence that is acceptably replaceable.