The self inductance L of a solenoid of length l and area of cross-section A, with a fixed number of turns N increases as

Options

A. I and A increase.
B. I decreases and A increases
C. I increases and A decreases.
D. both I and A decrease.

Answer

B

Explanation

Self inductance ,
`L=mu_r mu_0 n^2 Al = mu_r mu_0 (N/l)^2 Al [ because n=N/l]`
`L=(mu_r mu_0 N^2A)/l` [`mu_r , mu_0`, N=constant]
From equation it is clear that, `L prop A/l`
So to increase L , A should be increased while l should be decreased.