The Meissner effect is the expulsion of a magnetic field from a superconductor during its transition to the superconducting state.

This is the explanation by mainstream physics.

But the experiments show that they are not always expelled. They are attracted when they are little far away and repelled when they are close. There is a balanced point.

Total expulsion of magnetic flux can't explain the attractiveness.

Please give some comments on this.

  • $\begingroup$ Which experiments are you refering to exactly and are you aware of the difference between a type-1 and a type-2 superconductor? $\endgroup$ – By Symmetry Jul 4 '19 at 9:55
  • $\begingroup$ There are many superconductor and magnet levitation videos which show what I said. I think they are type 1, metal type. $\endgroup$ – Cang Ye Jul 4 '19 at 10:13
  • $\begingroup$ There are countless videos showing superconductor magnetic levitation. A superconductor is suspended on a magnet. It can also be suspended under a magnet. When it is on the magnet, the superconductor is repelled by the magnet. When it's under the magnet, it's obviously attracted by the magnet. $\endgroup$ – Cang Ye Jul 6 '19 at 2:28

I do not like the term "levitation" as it is misleading. I prefer something on the lines of "suspension".

When in the presence of a magnet a superconductor is neither repelled nor attracted to it. For the sake of this discussion, we can neglect type I and II superconductors. What actually happens is that the magnetic flux exclusion makes it such that the magnetic field lines wrap around the superconductor.

This wikipedia link shows a sketch of the magnetic field exclusion.

In this configuration the superconductor will not move up or down (of course if you apply enough force it will). It is trapped in its position. If you put the magnet on the bottom it looks like the superconductor is levitating. Conversely, if you put the magnet on top and pull it up, the superconductor will follow it so that its relative position does not change (again, it is trapped withing those magnetic field lines).

But beware, if the superconductor is heavy enough it will fall and you will like shatter your ceramic :-). Done that :-(.

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  • $\begingroup$ The mainstream explanation is exclusion of flux. In a uniform magnetic field, exclusion of flux doesn't give the ball any force. In a nonuniform field, like near the pole, or between two poles of a magnet, the superconducting ball will be repelled, not attracted. $\endgroup$ – Cang Ye Jul 7 '19 at 10:06
  • $\begingroup$ What I said is right. Take or leave it. Neither attraction nor repulsion... $\endgroup$ – rpsml Jul 7 '19 at 10:12
  • $\begingroup$ I know that it's trapped in a position, this is experiment fact. What I am asking is how to explain the trap. Mainstream explain it as total exclusive flux, do you believe the explanation? I don't. $\endgroup$ – Cang Ye Jul 7 '19 at 14:40
  • $\begingroup$ The demos using High $T_c$ material involve flux pinning/trapping on defects. They are not pure Meisner. $\endgroup$ – mike stone yesterday

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