Test: Hall Effect - Mechanical Engineering MCQ

The temperature at which a normal conductor loses its resistivity and becomes a super conductor is knows as transition temperature or critical temperature.

When the temperature is reduced to 0K, the resistivity of the impure metal doesn’t become zero, because there exist some impurities which gives rise to minimum resistivity known as residual resistivity.

A diamagnetic material has a tendency to expel magnetic lines of forces. Since the super conductor also expels magnetic lines of force it behaves as a perfect diamagnet. This behaviour is first observed by Meissner and is hence called Meissner effect.

When a large value of a.c. current is applied to a super conducting material it induces some magnetic field in the material and because of this magnetic field, the superconducting property of the material is destroyed.

 When dc current of large magnitude is once induced in a super conducting ring then the current persists in the ring even after the removal of the field. This current is called persistent current. This is due to diamagnetic property. The magnetic flux inside the ring will be trapped in it and hence current persists.

Since the current in superconducting ring can flow without any change in its value, it can be used as a memory or storage element in computers.

Critical field, H_c = H₀ [1-T²/(T_c)² )] Critical college = 0.02166 Tesla

Critical current I_c = 2πrH_c
I_c = 134.26 A