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Resistance in a superconductor
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Resistance

In a superconductor

In a superconductor, below a temperature called the “critical temperature”, the electric resistance very suddenly falls to zero. At zero resistance, the material conducts current perfectly. This is incomprehensible because the flaws and vibrations of the atoms should cause resistance in the material when the electrons flow through it. However, in a superconductor, the electric resistance is equal to zero although the flaws and vibrations still exist.

: In a superconductor, the electric resistance is equal to zero. This is why an electric current can circulate forever in a superconducting ring even when the battery has been unplugged! This is how magnetic fields are created in MRIs. It might seem odd that a battery could create a low voltage electric current at the terminals of a superconducting network, since the voltage should be equal to zero because of the absence of electric resistance. What happens is that the electric tension created by the battery is divided into the other parts of the network, i.e. the metallic wires that link the battery to the superconductor and to the interior of the battery (internal resistance).

The resistance is really equal to zero. The measurements taken over the course of several years show that the current never decreases. Even though the current is perpetual, it is not a violation of the thermodynamic laws (which forbids perpetual motion machines), because in this case no energy is created. The electric and magnetic energy is merely stored in the ring.

Explanation : the electrons form a new original quantum collective state that is not sensitive to collisions anymore. The electrons are not slowed, and the electric resistance has disappeared.

 On a microscopic scale, quantum physics teaches us that the electron behaves like a small wave. When there is a flaw or when one of the atoms of the crystal pattern is vibrating, the wave is disrupted.At a very low temperature, the electrons pair up and merge into one quantum wave that fills the whole material. This unique wave becomes insensitive to the flaws in the material; they are too small to slow the whole wave. The electric resistance has hence disappeared.

Measure of the electrical resistance in a superconductor.

 

CNRSSociété Française de PhysiqueTriangle de la physique
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CNRSSociété Française de PhysiqueTriangle de la physique