Magnetism

Electrical resistance of certain materials, known as superconductors, changes abruptly from a non-zero value to zero as their temperature is lowered below a critical temperature T_c(0). An interesting property of superconductors is that their critical temperature becomes smaller than T_c(0), if they are placed in a magnetic field, that is, the critical temperature T_c(B) is a function of the magnetic field strength B. The dependence of T_c(B) on B is shown in the figure.

A superconductor has T_c(0) = 100 K. When a magnetic field of 7.5 T is applied, its T_c decreases to 75 K. For this material, one can definitely say that when