# Meissner effect, thought experiment.

1. Apr 12, 2010

### isysdamn

This has been on my mind for a while now; and I really need some outside input to either expand or put this idea to rest.

So this idea relies on the Meissner effect; which during the transition of a material from a natural state to a superconducting state the magnetic permeability of that material approaches zero, or is zero... I'm not really convinced, but... Let us assume it is zero.

So you have a natural dipole magnet inside of a "special" cup that fits the magnet perfectly. When the "special" cup switches from it's natural state to it's superconducting state, what happens?

Cross-section of my idea:
http://meton.net/files/TEid1.png [Broken]

My thoughts are that the function of permeability during the phase change is linear; therefore there will by an asymptotic change in the magnetic field through the cup. And my thoughts are that the natural magnet will be ejected from the cup at intense velocity; nearly relativistic velocity.

But intuitively, i believe there must be a natural mechanic that will prevent his from occurring; I just can't think of one.

Anyway tear this idea apart; I welcome it.

Last edited by a moderator: May 4, 2017
2. Apr 12, 2010

### isysdamn

Grr. I hate this... I mean continuous when I said linear; a habit of them being one in the same in the math I'm immersed in right now.

3. Apr 13, 2010

### SpectraCat

Hmmm ... why do you think the acceleration will be so large? I have done Meissner effect experiments with ceramic super conductors, and the magnets just lift up gently to a height of a few mm ... they don't go shooting up into the air. However, I didn't use very strong magnets ... just little chips of magnetite. The force will be proportional to the magnetic flux density that is repelled from the surface, so you can probably get a more dramatic effect from stronger rare-earth magnets, and putting the magnet inside a cup as you have suggested seems like it will also amplify the effect. But in the end, you still just have F=ma, so I can't see how you would get anywhere near relativistic acceleration.

Last edited by a moderator: May 4, 2017
4. Apr 13, 2010

### ZapperZ

Staff Emeritus
As with SpectraCat, I've done this many times as demos and not sure why one would expect the expulsion of magnetic fields could cause such a tremendous force.

Furthermore, most superconductors are Type II, which means that as soon as it becomes superconducting, there are still flux lines penetrating various regions of the bulk material. It is only below a second critical temperature do you get a complete expulsion of these flux lines. What this means is that at the higher critical temperatures, these flux lines actually could "pin" the magnet from flying out because it field lines will try to resist from being twisted/changed.

Zz.