Find the mutual inductance of two long concentric solenoids for a length I. The area of cross-section of inner solenoid is A and number of turns per unit length are `n_(1)` and `n_(2)`.

Explanation

To find the mutual inductance of two long concentric solenoids, we can follow these steps:

### Step 1: Define the parameters
Let:
- Length of the solenoids = \( L \)
- Area of cross-section of the inner solenoid = \( A \)
- Number of turns per unit length of the inner solenoid = \( n_1 \)
- Number of turns per unit length of the outer solenoid = \( n_2 \)
...