Electrical resitance of certain materials, known as superconductors, changes abruptly from a nonzero value to zero as their temperature is lowered below a critical temperature Tc(0). An interesting property of superconductors is that their critical temperature becomes smaller than Tc(0) if they are placed in a magnetic field,i.e., the critical temperature TcB. is a function of the magnetic field strength B. The dependence of TcB. on B is shown in the figure.
A superconductor has Tc(0) = 100K. When a magnetic field of 7.5 Tesla is applied, its Tc decreases to 75K. For this material one can definitely say that when