A current of 200 μ A deflects the coil of a moving coil galvanometer through 60°. The current to cause deflection through π/10 radian is :

Solution

Physics sir · 3 steps

In a moving coil galvanometer the deflection is directly proportional to the current, so just scale by angle.

1. Current and deflection. In a moving coil galvanometer the restoring torque kθ balances the magnetic torque NIAB. So I = k/NAB θ, which means I ∝ θ.

   I₂/I₁ = θ₂/θ₁

2. Same units. Convert the first angle to radians: 60° = π/3. The ratio is (π/10)/(π/3) = 3/10.
3. So. I₂ = 200 μA × 3/10 = 60 μA, which is option (d).

The idea to keep. Current is proportional to deflection in a moving coil galvanometer. Put both angles in the same unit before you take the ratio.

Answer from the NTA final answer key. Solution by PrepWiser.