A magnet on top of a superconductor levitates and spins in mid air
when liquid nitrogen is poured over it.
This experiment is a great demonstration of the interesting properties of superconductors. Superconductivity occurs when certain materials are cooled below what is known as their critical temperature. These critical temperatures are very low, with the "warmest" one at 135 K (-138 Celsius) .When these substances reach these temperatures and below, the material has no electrical resistance and expels all magnetic fields from its interior. This effect will cause the magnetic fields of things like nearby magnets to be repelled, and causes the superconductor to exert a repulsive force on the magnets themselves. This is known as the Meissner effect.
In this experiment, a strong magnet is sitting on top of the superconductor. When the liquid nitrogen is poured over top, it cools the superconductor below its critical temperature. The magnetic fields are then repelled, and if the repulsive force is greater than the force of gravity, the magnet will levitate!
- Neodymium Magnet
- Styrofoam cup
- Liquid Nitrogen
Set the superconductor on top of the styrofoam cup (cut the top off the cup so you just have a shallow base).
Place the magnet on top of the superconductor.
Pour the liquid nitrogen over the magnet and superconductor.
Watch as the magnet lifts off the superconductor, and try giving it a spin.