Question

Electrical resistance of certain materials, known as superconductors, changes abruptly from a nonzero 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, i.e., 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.

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Linked Question 1

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

B = 5 Tesla, 75K < T_C (B) < 100 K

B = 10 Tesla, 75 K < T_C (B) < 100 K

B = 10 Tesla, T_C (B) = 70 K

B = 5 Tesla, T_C (B) = 80 K

${(T_{C})}_{5} > {(T_{C})}_{7 .5}$

${(T_{C})}_{5} < {(T_{C})}_{0}$

$\Rightarrow {(T_{C})}_{7 .5} < {(T_{C})}_{5} < {(T_{C})}_{0}$

$75 k < {(T_{C})}_{5} < 100 k$

Linked Question 2

In the graphs below, the resistance R of a superconductor is shown as a function of its temperature T for two different magnetic fields B₁ (solid line) and B₂ (dashed line). If B₂ is larger than B₁, which of the following graphs shows the correct variation of R with T in these fields ?

B₂ > B₁

$T_{C_{2}} < T_{C_{1}}$