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. `l` and A increase
B. `l` decreases and A increases
C. `l` increases and A decreases
D. both `l` and A decrease

Answer

B

Explanation

The self-inductance of a long solenoid of cross-sectional area A and length l , having n truns per unit length, filled the inside of the solenoid with a material of relative permeability (e.g.,soft iron, which has a high value of relative permeability) is given by
`L=mu_rmu_0n^2Al`
`n-N//l`