29. Superconductors are those elements A.Whose conductivity is intermediate between metals and insulators B.Whose resistance falls almost to zero at very low temperatures C.Which turn into insulators at very low temperatures D.Which conduct electricity only at super-high temperatures
Option B Solution: Superconductivity is a phenomenon of exactly zero electrical resistance and expulsion of magnetic fields occurring in certain materials when cooled below a characteristic critical temperature. It is characterized by the Meissner effect, the complete ejection of magnetic field lines from the interior of the superconductor as it transitions into the superconducting state. The electrical resistivity of a metallic conductor decreases gradually as temperature is lowered. In a superconductor, the resistance drops abruptly to zero when the material is cooled below its critical temperature. An electric current flowing in a loop of superconducting wire can persist indefinitely with no power source.
