Question

1. Give the reasons for the following statements:
   1. Superconductors are poor conductors of heat for temperature much below the transition temperature T_c, T << T_c.
   2. For different isotopes of the same element, the transition temperature of superconductor T_c depends on the isotope mass.                               
      25. marks)

Answer 1

a) In normal state, all free electrons participate in heat flow i. e. thermal conductivity; so the thermal conductivity is large. But in superconducting state, the materials have superelectrons and normal electrons, the superelectrons will not participate in thermal conductivity; so, thermal conductivity is less. As we go below Tc, the number of superelectrons will increases and normal electrons will decrease, that's why there will be very low thermal conductivity or heat flow. So, the materials at T much below Tc are very poor conductor of heat.

b) This is the isotope effect in superconductor which relates the transition temperatures with the mass of isotope as

Tc x √M = constant  

more mass , less transition temperature as it inversely proportional to √M.