A coil al a moving Coil galvanometer twists through `90^@` when a current of one microampere is passed through it. If the area of the coil is `10^-4 m^2` and it has `100` turns, calculate the magnetic field of the magnet of the galvanometer. Given, `k = 10^-8N -m /degree.`

Explanation

To solve the problem, we need to calculate the magnetic field (B) of the magnet in the moving coil galvanometer using the given parameters. We will use the relationship between the torque (τ) on the coil, the current (I), the area (A), the number of turns (n), and the magnetic field (B).

### Step-by-Step Solution:

1. **Understand the relationship**: The torque (τ) acting on the coil in a magnetic field is given by the formula:
\[ τ = n \cdot B \cdot I \cdot A \cdot \sin(θ) \]
...