A rectangular coil of 100 turns has length 5 cm and width 4 cm. it is placed with its plane parallel to a uniform magnetic field and a current of 2 A is sent through the coil. Find the magnitude of the magnetic field B, if the torque acting on the coil is `0.2 Nm^(-1).`

Explanation

To solve the problem, we need to find the magnitude of the magnetic field \( B \) acting on a rectangular coil given the torque \( \tau \), number of turns \( N \), current \( I \), length \( l \), and width \( w \) of the coil.

### Step-by-Step Solution:

1. **Identify Given Values:**
- Number of turns, \( N = 100 \)
- Length of the coil, \( l = 5 \, \text{cm} = 0.05 \, \text{m} \)
- Width of the coil, \( w = 4 \, \text{cm} = 0.04 \, \text{m} \)
...