Question

Can we use the onset of successful magnetic levitation to provide an estimate of the critical temperature? on a superconductivity lab.

Answer 1

EXPLANATIONS:

1. Superconductors repel magnetic fields due to the Meissner effect. Near the surface of the superconductor material, small currents flow (without any resistance) that make an opposite magnetic field that repels the field from the magnet.

2. We found that it doesn't behave like a pair of magnets repelling one another. With two magnets repelling, the force varies with how far apart the two magnets are. The closer the magnets, the greater the force.

3. With the superconductor, we could get levitation to happen 1/8" away or 1/4" away equally well. We also had to hold it there for a moment to get it stable. Why does it levitate in a stable way? Why doesn't the repulsion simply keep pushing away like a pair of magnets would? We found that flux-pinning is a good explanation.

4. The levitation process is quite remarkable. Since the levitating currents in the superconductor meet no resistance, they can adjust almost instantly to maintain the levitation. The suspended magnet can be moved, put into oscillation, or even spun rapidly and the levitation currents will adjust to keep it in suspension.

5. The Meissner effect in superconductors like this black ceramic yttrium basedsuperconductor acts to exclude magnetic fields from the material. Since the electrical resistance is zero, supercurrents are generated in the material to exclude the magnetic fields from a magnet brought near it. The currents which cancel the external field produce magnetic poles which mirror the poles of the permanent magnet, repelling them to provide the lift to levitate the magnet.