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Super conductivity

This is an excellent demo of super conductivity. The liquid is liquid nitrogen. The disk is a magnet. The black block is the super conducting (SC) material (but becomes SC only below its critical temperature, somewhat higher than liquid nitrogen).

When warm, the block has no particular magnetic / electric properties. When cooled, it becomes a SC. One of the properties of a SC is that magnetic fields can be pinned in place in the SC.

A moving magnetic field generates eddie currents within conductors, and can be felt as a resistance to relative motion. In most materials, this current quickly decays due to electrical resistance. In SC, eddie currents do not decay, but instead will tend to hold the magnetic field in place.

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