Johan,johanfprins wrote:Because I have never said so! I have consistently stated that the "applied electric field" IS CANCELLED!!! And therefore there is no electric field which can accelerate charge carriers.icarus wrote:Why didn't you address my first and most obvious point that you are wrong in saying that 'there is no electric-field' since this implies it does not exist at all
I never said that it "does not exist at all". I cannot help to question the motives of somebody who tries to put words in my mouth. This is an old trick to obfuscate a discussion. So PLEASE refrain!This is exactly what I have stated all along: The applied electric is cancelled: Your idea that it "tends to a null vector fied" without giving a physics reason why and how it achieves this, is Voodoo. I am clearly saying that an applied electric field can ONLY be cancelled by an opposite polarisation field. If you know Maxwell's equations, as you claim you do, you should realise that there is no other way in which an applied electric field can be cancelled ever.Begin here,
E = - grad(phi)
What you might be able to say is that that the electric field tends to a null vector field.Why can you not measure the latter directly? It is simple to measure the voltage difference over different distances: If this were not so we would not have been able to control electricity and/or electronics.Although the e-field is not measured directly but only through the gradient of the potential (voltage) which is probably not measured directly either ...
My guess is that you deliberately want to obfuscate the simple physics involved. The fact remains that there is no voltage difference between any two points. This means in "real physics" that charge-carriers cannot be accelerated. And this means from Newton's second law that there is no net force and thus no net electric field!I repeat: If you read carefully I did not categorically state the "non-existence" of the field but the "cancellation of the applied field" so that it cannot accelerate charge carriers. This is an experimental fact not "a leap of faith".so categorically stating the non-existence of the electric field requires an objection to Maxwell's equations, and a leap of faith.Again you are trying to obfuscate the issue by applying mathematics which does not relate in any way to a steady-state condition when a steady-state current is flowing; which according to Ampere's law generates a time-independent magnetic field. Go to ANY text book on Electrodynamics and you will see that for steady-state conditions the magnetic field (and thus its vector potential) DOES NOT CHANGE WITH TIME. So to include a time-changing vector potential as if it manifests when an equilibrium current is flowing through a superconductor is not based on ANY experimental fact or known physics: It is physics nonsense: Voodoo.The time-dependent part cannot either be ruled out so categorically either unless you have somehow measured the mag. vector potential across the entire frequency spectrum for oscillatory, yet time-averaged zero-field components, good luck with that.To again repeat: Please do not put words in my mouth: I have consistently said that the applied electric field is "cancelled" so that it cannot accelerate charge-carriers: Or do you believe that charge-carriers are being accelerated within a superconductor? If the latter is the case, why is the potential difference zero?If the 'no electric field' argument is the crux of your SC argument it seems mathematically shaky since the electric field is a derived quantity so postulating its non-existence is nonsense from the beginning.It implies nothing since what you are stating is Voodoo with no experimental basis. What I am stating is fact: If a current flows between two contacts without a potential difference over the contacts, then there CANNOT be a net electric field accelerating charge carriers. If this is not so it would mean that Newton's laws are wrong. And I am not yet willing to reject Newton's laws just because you want me to ignore them.Lets just say it tends to zero in some limiting behavior ... and then consider what that implies for the gradients and their boundary conditions of your SC region.
Forgive me for some rather simple comments. Ch 23 of your book rests on the apparent contradiction that charge carriers appear to move in a superconductor but cannot be accelerated or deccelarated, because of the zero field.
I have not looked too deeply at this, but remembering vaguely some QM I would guess:
This is a semi-classical treatment of a quantum system. In (the standard model of) a superconductor the wave functions are highly nonlocalised so that non-local effects exist between interaction at different separated points. The electron Cooper pairs as a whole form a Bose-Einstein condensate with QM addition and subtraction operators. In this context charge can be added at one point, subtracted at another, and a QM description of the whole system is needed to see precisely what is going on?
The apparent contradiction relating to acceleration and decelleration does not exist because the eletrons are highly nonlocal and therefore do not move.
Forgive me if I have made a mistake here.
Bet wishes, Tom