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#6974 - 05/21/06 08:51 PM "Eddy" currents in a superconductor
Johnny Boy Offline
Senior Member

Registered: 11/29/05
Posts: 330
Loc: South Africa
On one of the previous topics the following advice was given: "If hundreds of thousands of physics grad students across the planet over 70 years have gone through this from postulates to final derived theory and nobody has found an error, including experimentalists, then you don't".
Afterwards I found out that this statement is not quite true; for example, there are a substanrial number of grad students having obtained their PhD's in Quantum Field Theory who have raised objections, and believe that they have found errors; but as soon as they propagated this viewpoint they suddenly found that they could not get their articles published in peer reviewed journals anymore. One can now reason that the reviewers proved these objections wrong; however, in general these papers have been rejected by using vague terms; for example, that the objections are "too vague" or "too speculative". No real scientific arguments were used to justify the decision. So maybe the hundreds of thousands of grad students who did not report their dissent did not do so becaause of the dire consequences they feared for their careers. Maybe peer review has become an instrument to protect the top structure of scientists through which funding is allocated to the hundres of thousands of grad students, causing them to then end up having scientific frontal lobotomies?
It made me think about the following possibility: could it not have happenned that a scientific concept becomes so dogmatically accepted that hundreds of thousands of supervisors go into appoplexy when it is challenged? And this discourages grad students to re-investigate it from first principles? This would mean that an error can go on for many years, mybe even 100 or more, without being re-examined critically in terms of basic scientific principles.
What I propose to do is to raise simple topics, which have been accepted for many years (50 or more)as having passed the test of hundreds of thousands of students (and their professors) and get the participants of this forum to re-examimine the validity of the concept from basic principles.
In this thread I start off by raising the mechanism for the generation of circular currents within a superconductor which finds itself within a magnetic field.

Consider a supercondutor across which a magnetic field is generated by switching on an electromagnet so that a magnetic field increses from zero to a value B. It has been experimentally verified many times that circular currents are generated within the superconductor. They cause an opposite magnetic field that cancels the applied magnetic field, so that there is no magnetic field within the superconductor. Now the textbook question: what is the mechanism that forces the superconducting charge carriers to move in circles? Your answers will be appreciated.

What do you say Uncle Al and D A Morgan?
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#6975 - 05/22/06 05:33 PM Re: "Eddy" currents in a superconductor
Uncle Al Offline
Superstar

Registered: 10/17/04
Posts: 540
Loc: Southern California
Look up the difference between Type I supercons and Type II supercons. BTW, superconductivity is strictly a DC phenomenon. Ramping up an external external field or changing current must create losses.
_________________________
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http://www.mazepath.com/uncleal/
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http://www.mazepath.com/uncleal/qz3.pdf

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#6976 - 05/22/06 07:44 PM Re: "Eddy" currents in a superconductor
Johnny Boy Offline
Senior Member

Registered: 11/29/05
Posts: 330
Loc: South Africa
Quote:
Originally posted by Uncle Al:
Look up the difference between Type I supercons and Type II supercons. BTW, superconductivity is strictly a DC phenomenon. Ramping up an external external field or changing current must create losses.
That is not an answer to my question. I am still asking what is the mechanism responsible for creating the circular currents?
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#6977 - 05/22/06 08:02 PM Re: "Eddy" currents in a superconductor
dr_rocket Offline
Member

Registered: 12/06/06
Posts: 196
Loc: Palo Alto, CA, USA
Hi Jonny Boy,

I like what you are suggesting. I am a big fan of "to re-investigate it from first principles".

I must say, however, that you run the risk of being misunderstood. As you say generations of scientists and their students have been blindly accepting many things in an uncritical manner. So when you pose the question - some - readers will tend to misunderstand what you are driving at. Rather than dig into what you have to say and formulate a meanigful response they will:
a) come up with a reply that shows they missed the point;
b) heap on the ridicule and sarcasm;
c) spew total nonsense.

Rather than these three pointless alternatives I will make an effort. First I am no expert at superconducting, so I have no particular insight into your question. Now your question is this:

"what is the mechanism that forces the superconducting charge carriers to move in circles? "

One of the basics of any problem solving or analytic activity is to ask what the object of study reminds you of.

My first level take on this is to think of charges moving in a magnetic field. This bring to mind the Lorentz force law: Fm = qv X B.

My second level take is to think about Faraday induction. This is where a magnet is thrust through a coil of wire to produce a current. I am also thinking of Lenz' law in this context.


Now I look back at the original question and notice that you said "superconducting charge carriers". Whoa! Shouldn't it be the charge carriers in the superconducting material?

Well, I guess that this is where I have to ask a question or two. The most important is what is the basic principle you wish to call into question? Maybe you could also specify what state that the superconductor is in when the B field is built up. Does it have a current in it already? Would bringing a bar magnet near the material make any difference (as opposed to a solenoid where the field is "made") in what you are asking?

What ever you do, don't take my questions in a negative way. I am only asking you to sharpen the point.

Dr R.

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#6978 - 05/23/06 12:35 PM Re: "Eddy" currents in a superconductor
Johnny Boy Offline
Senior Member

Registered: 11/29/05
Posts: 330
Loc: South Africa
Quote:
Originally posted by dr_rocket:
One of the basics of any problem solving or analytic activity is to ask what the object of study reminds you of.

My first level take on this is to think of charges moving in a magnetic field. This bring to mind the Lorentz force law: Fm = qv X B.

My second level take is to think about Faraday induction. This is where a magnet is thrust through a coil of wire to produce a current. I am also thinking of Lenz' law in this context.


Now I look back at the original question and notice that you said "superconducting charge carriers". Whoa! Shouldn't it be the charge carriers in the superconducting material?

Dr R.
Dr R. you have made my day. You gave the answer that you will find in all textbooks right up to the present. The currents are induced by Faraday's law of induction; even when the magnetic field is switched on over a material that is already in the superconducting state. An equivalent way would be to push a bar magnet towards the material. Now let us quote Feynman on this issue (Feynman lectures volume III pragraph 21-6): "If, as you build up the magnetic field, any of it were to build up inside the metal (in its superconducting state), there would be a rate of change of flux which would produce an electric field, and an electric field would immediately generate a current which, by Lenz's law, would oppose the flux".

Thus it is generally accepted, even by Feynman, that these currents are generated and driven by an electric field. There is only one problem: when an electric field drives a current, the material CANNOT be a superconductor. To be a superconductor a current must flow without any electric field responsible for the flow, or else, according to Ohm's law, the potential between two contacts cannot be zero; and therefore the resistance cannot be zero.

Why did the hundred's of thousand's of PhD students and their supervisors not pick up this impossibility over the last 70 years?

I have a good reason for using "superconducting charge carriers" which I will not elaborate on just now.
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#6979 - 05/23/06 04:14 PM Re: "Eddy" currents in a superconductor
Count Iblis II Offline
Senior Member

Registered: 01/21/05
Posts: 375
Quote:
You gave the answer that you will find in all textbooks right up to the present
Not true at all! Go to the library and read this book:

G. Rickayzen, Theory of Superconductivity (Interscience Publishers, New York, 1965).

You have to distingiush between rigorous theory and what is taught in high school and the first few years in university. The book by Rickayzen gives a rigorous derivation of the Meissner effects starting from BCS theory.

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#6980 - 05/23/06 06:23 PM Re: "Eddy" currents in a superconductor
Johnny Boy Offline
Senior Member

Registered: 11/29/05
Posts: 330
Loc: South Africa
Quote:
Originally posted by Count Iblis II:
Quote:
You gave the answer that you will find in all textbooks right up to the present
Not true at all! Go to the library and read this book:

G. Rickayzen, Theory of Superconductivity (Interscience Publishers, New York, 1965).

You have to distingiush between rigorous theory and what is taught in high school and the first few years in university. The book by Rickayzen gives a rigorous derivation of the Meissner effects starting from BCS theory.
I am NOT talking about the Meissner effect here. That is a different issue that I am willing to deal with on another occasion. Do not advise me to read a book if you are not mentally capable of providing the answer yourself. Feynman stated clearly that the charge carriers react to an electric field. Do you agree or not?

By the way BCS is a misnomer; it should have been called BS theory!
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#6981 - 05/23/06 08:45 PM Re: "Eddy" currents in a superconductor
dr_rocket Offline
Member

Registered: 12/06/06
Posts: 196
Loc: Palo Alto, CA, USA
I have to agree with Count Iblis II on this one. When one is proposing a novel theory to replace another, some things are absolutely required. The first is a solid knowledge of the theory you mean to replace. You should be able to say exactly what is wrong with the current theory and how yours is going to fix it. Your theory, or any theory for that matter, should be based on matters of fact, i.e., experiments or careful observation.

It is one thing to say that Bardeen's idea of electron-phonon coupling is BS and another to say explicitely what is wrong with it. Quite a bit could be said in this regard as it is clearly not a perfect or complete theory.

You need to be careful about using terms like "superconducting charge carriers". It is too easily misunderstood. A charge carrier is an electron, proton, ion etc. and their motions constitute a current. The quoted phrase seems to indicate that charge carriers have an additional property beside the electric charge.

Frankly, your words "I will not elaborate on just now" seem like a dodge. How about a few hints?

Having said that, I will not deny that textbooks can be very wrong and that doddering old university profs have gone insensitive to new possibilities.

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#6982 - 05/23/06 10:31 PM Re: "Eddy" currents in a superconductor
Count Iblis II Offline
Senior Member

Registered: 01/21/05
Posts: 375
Quote:
Originally posted by Johnny Boy:
Quote:
Originally posted by Count Iblis II:
Quote:
You gave the answer that you will find in all textbooks right up to the present
Not true at all! Go to the library and read this book:

G. Rickayzen, Theory of Superconductivity (Interscience Publishers, New York, 1965).

You have to distingiush between rigorous theory and what is taught in high school and the first few years in university. The book by Rickayzen gives a rigorous derivation of the Meissner effects starting from BCS theory.
I am NOT talking about the Meissner effect here. That is a different issue that I am willing to deal with on another occasion.
No the Meissner effect is precisely the effect you are talking about. It is the screening of magnetic fields inside a superconductor. You may object and say that you want to know what exactly happens when you switch on the magnetic field and how the currents arise that give rise to the screening. However, if you want to prove that the Meissner effect does indeed arise in a superconductor you must go into precisely these details and treat the dynamic problem (you want to consider what happens at late times, long after the magnetic field is whitched on). This is explained in detail in the book by Rickayzen.


Quote:

Do not advise me to read a book if you are not mentally capable of providing the answer yourself. Feynman stated clearly that the charge carriers react to an electric field. Do you agree or not?
Of course, charge carriers react to an electric field. In fact, electromagnetic fields are the only (significant) thing they can react to.

Feynman in his books is trying to explain complicated things to undergraduate students who haven't studied advanced quantum mechanics yet. You need to understand the field theoretical methods applied to many particle systems to derive the Meissner effect rigorously.

Quote:

By the way BCS is a misnomer; it should have been called BS theory!
Why then not submit your theory here ? If your paper is unfairly rejected then you can come back here and let us see the (unreasonable) referee report. B.t.w. alternative theories on superconductivity do exist and are accepted in journals like PRB, see e.g. here.

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#6983 - 05/23/06 10:43 PM Re: "Eddy" currents in a superconductor
Count Iblis II Offline
Senior Member

Registered: 01/21/05
Posts: 375
Quote:
There is only one problem: when an electric field drives a current, the material CANNOT be a superconductor. To be a superconductor a current must flow without any electric field responsible for the flow, or else, according to Ohm's law, the potential between two contacts cannot be zero; and therefore the resistance cannot be zero.
And what happens after the driving field caused by changing the magnetic field from zero to B has vanished?

Ohm's law is not a fundamental law. As Uncle Al posted here, superconductors only have zero resistance to DC currents. When you switch on fileds then you cause a response that cannot be calculated directly using some ''Ohm's Law''. You need to start from the fundamental theory that describes the electrons in the metal.

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#6984 - 05/24/06 12:56 AM Re: "Eddy" currents in a superconductor
Uncle Al Offline
Superstar

Registered: 10/17/04
Posts: 540
Loc: Southern California
Has somebody told the git that Cooper pairs have conjugate momenta? The two electrons are traveling in opposite directions.

Google
"cooper pairs" "conjugate momenta" 55 hits
"cooper pairs" "conjugate momentum" 114 hits

Ignorance is educable, stupidity is forever. Make your choice Johnny Boy.,

http://www.mazepath.com/uncleal/horse.htm
_________________________
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz3.pdf

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#6985 - 05/24/06 10:07 AM Re: "Eddy" currents in a superconductor
Johnny Boy Offline
Senior Member

Registered: 11/29/05
Posts: 330
Loc: South Africa
Great responses; just what I wanted. By using the vector potential in the Schroedinger equation to so-call "explain" the Meissner effect still assumes that the "Cooper pairs" respond to an electric field; i.e. they are accelerated to reach an appropriate velocity in order to cancel the applied magnetic field. The interaction between a charged particle, whether an electron or a boson (which internally have conjugate momenta - what ********!) is still through an induced electric field. The electric field is either induced by the magnetic field changing (Faraday effect) or by the charge moving relative to the magnetic field (F=vxB).

Now this argument is a beaut: "And what happens after the driving field caused by changing the magnetic field from zero to B has vanished?" Correct then there is no electric field and the current proceeds without an electric field being present. So this "explains" superconduction for circulating currents (well not quite; see below); however, superconducting currents also manifest linearly between two contacts, and when you increase the emf of the circuit in which the superconductor forms an element, the velocity of the carriers increases, which implies that they respond to an electric field. BUT in this case the electric field cannot go to zero because of an externally applied magnetic field becoming stationary!! So what happens to the electric field?

As indicated above there is another problem with circulating currents after the electric field disappeared: Why do the circulating currents NOT dissipate by radiating electromagnetic waves? After all, one can increase their circular velocity by increasing the magnetic field; which implies that their kinetic energy has increased. It is known that when you generate circular currents around a ring and switch off the magnetic field, you trap magnetic field energy around the ring. This means that the circulating current should radiate electromagnetic waves as long as its movement can be sustained by the presence of the trapped magnetic field. Once this energy is used up, the circulating currents should stop. Why is this not observed experimentally? It cannot be explained in terms of BCS theory.

I have submitted a paper four months ago and am still waiting for a reply. When I get it I will post it on this thread.

O yes I nearly forgot the following response: "Ohm's law is not a fundamental law. As Uncle Al posted here, superconductors only have zero resistance to DC currents. When you switch on fileds then you cause a response that cannot be calculated directly using some ''Ohm's Law''. You need to start from the fundamental theory that describes the electrons in the metal."

So what you are saying is that when the electric field changes, the reaction is not that of a superconductor. I can apply an external magnetic field so that it increases in intensity at a constant rate. The induced electric field will then be constant at all times until the magnetic field reaches its maximum value. Thus the charge carriers are accelerated by a constant electric field. One would thus expect that they will always be accelerated between two electrical contacts. This would mean that there is a potential difference between the two contacts. This, in turn, would mean that you do not have superconduction even though the carriers are not scattering within the material; this is similar to the electrons in a vacuum diode NOT forming a superconducting phase.
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#6986 - 05/24/06 10:36 AM Re: "Eddy" currents in a superconductor
Johnny Boy Offline
Senior Member

Registered: 11/29/05
Posts: 330
Loc: South Africa
Quote:
Originally posted by Uncle Al:
Has somebody told the git that Cooper pairs have conjugate momenta? The two electrons are traveling in opposite directions.

Google
"cooper pairs" "conjugate momenta" 55 hits
"cooper pairs" "conjugate momentum" 114 hits

Ignorance is educable, stupidity is forever. Make your choice Johnny Boy.,

http://www.mazepath.com/uncleal/horse.htm
It seems you have already long ago made the second choice!
_________________________
http://www.cathodixx.com

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#6987 - 05/24/06 12:18 PM Re: "Eddy" currents in a superconductor
Count Iblis II Offline
Senior Member

Registered: 01/21/05
Posts: 375
Johnny Boy, please visit this page.

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#6988 - 05/24/06 01:54 PM Re: "Eddy" currents in a superconductor
Johnny Boy Offline
Senior Member

Registered: 11/29/05
Posts: 330
Loc: South Africa
Quote:
Originally posted by Count Iblis II:
Johnny Boy, please visit this page.
I know about this page and have myself experienced similar situations; hoewever, I never assume upfront that the person might not have a point until after I can refute his/her arguments by sound scientific arguments. You are not doing this, and the page you referred me to does not apply to me. Please try to argue logically on your own without just referring to books and funny pages. You might start to learn some science!
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#6989 - 05/24/06 04:44 PM Re: "Eddy" currents in a superconductor
Count Iblis II Offline
Senior Member

Registered: 01/21/05
Posts: 375
Quote:
Originally posted by Johnny Boy:
Quote:
Originally posted by Count Iblis II:
Johnny Boy, please visit this page.
I know about this page and have myself experienced similar situations; hoewever, I never assume upfront that the person might not have a point until after I can refute his/her arguments by sound scientific arguments. You are not doing this, and the page you referred me to does not apply to me. Please try to argue logically on your own without just referring to books and funny pages. You might start to learn some science!
Your arguments have already been refuted here. But you simply refuse to accept that and then you introduce new nonsensical arguments like that radiation should be emitted by the currents.

It is simply not possible to explain in detail why your arguments are wrong because then I would have to explain everything from basic electromagnetism to the theory of superconductivity to you. So, the link I referred you to, specifically points 15 and 16, do apply to you:

Quote:
"You have to spend some time studying my theory."
How much time did you spend getting an education in physics?

"Why don't you spend some time telling me what's wrong with my theory?"
Why don't you take a course? That's what they're for: So that many people can be taught the same thing at the same time, making more efficient use of the instructor's time. The instructor's office hours are for those who already took their own time studying the course material.

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#6990 - 05/24/06 05:44 PM Re: "Eddy" currents in a superconductor
Johnny Boy Offline
Senior Member

Registered: 11/29/05
Posts: 330
Loc: South Africa
Quote:
Originally posted by Count Iblis II:
It is simply not possible to explain in detail why your arguments are wrong because then I would have to explain everything from basic electromagnetism to the theory of superconductivity to you. So, the link I referred you to, specifically points 15 and 16, do apply to you:
What specifically has been refuted? It is clear that you are incapable of reasoning logically! How about starting with high school physics; although it is clear to me that it will be WAAAAAY above your head! Usually when a person really understands physics it is quite easy to refute a wrong argument without having to start off with Pythagoras (he was a Greek philosopher and one of the first mathematicians-you most probably will not know that!)
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#6991 - 05/24/06 05:49 PM Re: "Eddy" currents in a superconductor
Johnny Boy Offline
Senior Member

Registered: 11/29/05
Posts: 330
Loc: South Africa
Quote:
Originally posted by Count Iblis II:
Your arguments have already been refuted here. But you simply refuse to accept that and then you introduce new nonsensical arguments like that radiation should be emitted by the currents.
Have you ever heard about Maxwell's equations? When charges are moving in a circle, they accelerate towards the centrum and therefore they have to emit electromagnetic radiation. In fact, this is the reason why the Rutherford model of the atom (do you know about it?) had to be rejected!! What is nonsensical about this???

Have you ever heard about a microwave oven? Have you ever heard about a magnetron? The magnetron generates the microwaves! How does it do it? By having electrons moving in circles. Tsk, tsk, tsk; and you want to teach ME about electromagnetism. I hope you are not a professional scientist; or else I despair about our future. Oh, and furthermore, when the electrons move in a circle within a magnetron, they do not scatter; so according to BCS they must be forming a superconducting state: Yes?
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#6992 - 05/24/06 06:00 PM Re: "Eddy" currents in a superconductor
Johnny Boy Offline
Senior Member

Registered: 11/29/05
Posts: 330
Loc: South Africa
Quote:
Originally posted by Count Iblis II:
"You have to spend some time studying my theory."
How much time did you spend getting an education in physics?

"Why don't you spend some time telling me what's wrong with my theory?"
Why don't you take a course? That's what they're for: So that many people can be taught the same thing at the same time, making more efficient use of the instructor's time. The instructor's office hours are for those who already took their own time studying the course material.
[/QUOTE]

Where have I asked these questions? I am criticising presently accepted perceptions; not asking you to "study my theory" or to "show me where MY theory is wrong". Really I think you need some professional help!
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#6993 - 05/24/06 09:33 PM Re: "Eddy" currents in a superconductor
Count Iblis II Offline
Senior Member

Registered: 01/21/05
Posts: 375
Quote:
Originally posted by Johnny Boy:
Quote:
Originally posted by Count Iblis II:
Your arguments have already been refuted here. But you simply refuse to accept that and then you introduce new nonsensical arguments like that radiation should be emitted by the currents.
Have you ever heard about Maxwell's equations? When charges are moving in a circle, they accelerate towards the centrum and therefore they have to emit electromagnetic radiation. In fact, this is the reason why the Rutherford model of the atom (do you know about it?) had to be rejected!! What is nonsensical about this???

I think you are the one here who doesn't understand electromagnetism. If you did then you would know what is wrong with your argument.

Have you ever derived the formulas for radiation emitted by accelerated charges? Oviously not! If you just pick up a book like e.g. the book by Jackson then you will see that a circular current does not emit any radiation. If you have a steady current then the fields are constant and that cannot gove rise to radiation. The fact that charges are accelerated is not relevant.

If you have a single charge that is accelerated then you do have radiation. But the reason for that radiation is the way the fields from that accelerated charge behave.

Of course, I cannot be very precise here so don't try to argue with me on these points based on imprecise language.

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