The Meissner Effect

When a superconducting material, usually a ceramic alloy, is cooled below its initiation point it will have no resistance. When the superconducting material has zero resistance it becomes diamagnetic, meaning the material will generate surface currents that create their own magnetic field in the opposite direction of an externally applied magnetic field. This will cancel out all magnetic field inside the superconductor. When the superconductor and magnet are brought close together, and a slight force is given to the levitating magnet or superconductor it will just return to its equilibrium position. If the magnet and superconductor are forcibly removed from each other then the superconductor’s current and field will dissipate.

The Meissner effect may be reminiscent of the behaviour in classical physics known as Lenz’s law, which says a changing magnetic flux induces a current and magnetic field in a conductor that opposes the changing field. This, however, cannot explain the superconducting magnet in the Meissner effect. In the classical scenario the current lasts only as long as the field is changing a described by Faraday’s law. One might think the superconductor gets by this by having zero resistance, therefore once a current is induced it stays the same, but this is not the case and is only explainable by modern physics. Electrons in a superconductor that is below its critical temperature form pairs and these pairs move through an ion lattice at resonance with the lattice so they do not collide with any ions.

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