A current l = 1.5 A is flowing through a long solenoid of diameter 3.2 cm, having 220 turns per cm. At its centre, a 130 turn closely packed coil of diameter 2.1 cm is placed such that the coil is coaxial with the long solenoid. The current in the solenoid is reduced to zero at a steady rate in 25 ms. What is the magnitude of emf induced in the coil while the current in the solenoid is changing?

Explanation

To solve the problem of finding the magnitude of the emf induced in the coil while the current in the solenoid is changing, we can follow these steps:

### Step 1: Identify the given values
- Current in the solenoid, \( I = 1.5 \, \text{A} \)
- Diameter of the solenoid, \( D = 3.2 \, \text{cm} = 0.032 \, \text{m} \)
- Number of turns per cm in the solenoid, \( n = 220 \, \text{turns/cm} = 22000 \, \text{turns/m} \)
- Number of turns in the inner coil, \( N' = 130 \)
- Diameter of the inner coil, \( D' = 2.1 \, \text{cm} = 0.021 \, \text{m} \)
...