Electrical resistance of certain materials, known as superconductors, changes abruptly from a nonzero value of zero as their temperature is lowered below a critical temperature `T_(C) (0)`. An interesting property of super conductors 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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In the graphs below, the resistance R of a superconductor is shown as a function of its temperature T for two different magnetic fields `B_1`(solid line) and `B_2` (dashed line). If `B_2` is larget than `B_1` which of the following graphs shows the correct variation of R with T in these fields?

Options

A.
B.
C.
D.

Answer

A

Explanation

(a) From the given graph it is clear that with increase of the magnitude of magnetic field (B), the critical temperature `T_(C) (B)` decreases.
Given `B_2gtB_1`. Therefore for `B_2`, the temperature at which the resistance becomes zero should be less. The above statement is true for graph (a).