The Universe in Colour: The Meissner Effect

This isn’t an action shot of a cube of metal as it falls to the ground. This is real life levitation.

That cube of metal (actually it’s a magnet) is suspended in its position by its own magnetic field, and its interaction with the super-cooled superconductor beneath it.

Superconductors are materials which have zero internal resistance to electric currents flowing through them. If you induced a current within a superconductor, it would happily flow through it for millennia without being diminished. This property makes superconductors highly prized materials.

The problem with superconductors is that all the ones we currently know of require being kept at an extremely low temperature in order to functon. The highest temperature superconductor we’ve currently discovered is hydrogen sulphide, with a superconductor transition temperature of 203K – that means it’s only a superconductor below a temperature of -70 degrees centigrade!

It is a Holy Grail of modern materials science to find a superconductor that can operate at room temperatures.

The Meissner Effect

The effect that’s being demonstrated in the image above is what’s known as the Meissner effect. When a superconductor is super-cooled, it expels all magnetic fields from itself – no magnetic field lines can enter the superconductor.

So when a magnet is placed above the superconductor, what happens is that the magnetic field produced by the magnetic is expelled by the superconductor, and forces the magnet to hover just above it.

Here is a schematic below of what’s going on:

A normal situation with a ceramic disc magnet. The magnetic field lines leave the north pole and enter the south pole. A magnet sitting on the surface of a disc of superconducting material. The magnetic lines penetrate the surface. After critical temperature is reached the magnet lines can no longer penetrate the surface. The magnet is levitated above the superconductor.

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