Explanation:

Superconductors :

• Superconductivity is a set of physical properties observed in certain materials where electrical resistance vanishes and magnetic flux fi elds are expelled from the material. Any material exhibiting these properties is a superconductor .
• Unlike an ordinary metallic conductor, whose resistance decreases gradually as its temperature is lowered even down to near absolute zero, a superconductor has a characteristic critical temperature below which the resistance drops abruptly to zero.
• An electric current through a loop of superconducting wire can persist inde fi nitely with no power source
• Like ferromagnetism and atomic spectral lines, superconductivity is a phenomenon that can only be explained by quantum mechanics.
• It is characterized by the Meissner effect, the complete ejection of magnetic fi eld lines from the interior of the superconductor during its transitions into the superconducting state.