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

Options

A. `B =5 Tesla, T_(C) (B) = 80 K`
B. `B =5 Tesla, 75 KltT_(C) (B) lt 100 K`
C. `B =10 Tesla, 75 KltT_(C) (B) lt 100 K`
D. `B =10 Tesla, T_(C) (B) =70 K`

Answer

`B`

Explanation

`T_(C) (0) =100 K` and `T_(C) (for B =7.5 T) =75 K`
`IT` follows that
`T_(C) (0) =T_(C) (for B =5T) gt T_(C) (for B =7.5T)`
Since the critial temperature decreases with increase in magnetic field
`75 KltT_(C) (for B =5T) lt 100 K`
So the correct choice is `(B)` .