# The total number of turns and cross-section area in a solenoid is fixed.

Question:

The total number of turns and cross-section area in a solenoid is fixed. However, its length $\mathrm{L}$ is varied by adjusting the separation between windings. The inductance of solenoid will be proportional to:

1. (1) $\mathrm{L}$

2. (2) $\mathrm{L}^{2}$

3. (3) $1 / \mathrm{L}^{2}$

4. (4) $1 / \mathrm{L}$

Correct Option: , 4

Solution:

(4) Inductance $=\frac{\mu_{0} N^{2} A}{L}$