Supeconductivity
Ordinary conductors of
electricity become better conductor at lower temperatures. The ability of certain
metals, their compounds and alloys to conduct electricity with zero resistance
at very low temperatures is superconductivity. The materials which exibit his
property are called superconductors.
The phenomenon of superconductivity was first observed by
Kammerlingh Onnes in 1911. He found that mercury suddenly showed zero
resistance at 4.2K. The first theoretical explaination of superconductivity was
given by Bardeen, Cooper and Schrieffer in 195 and it is called the BCS theory.
The temperature at which electrical resistivity of
material suddenly drops to zero and the material changes from normal conductor
to superconductor is called the transition temperature or critical temperature
Tc. At the transition temperature the following changes are
observed:
(i)
The electrical
resistivity drops to zero.
(ii)
The
conductivity becomes infinity
(iii)
The magnetic
flux lines are excluded from the maerial.
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