Question

The number of turns of the coil of a moving coil galvanometer is increased in order to increase current sensitivity by $50 \%$ The percentage change in voltage sensitivity of the galvanometer will be:

• A. $50 \%$
• B. $75 \%$
• C. $0 \%$
• D. $100 \%$

Hint:

Voltage sensitivity of a moving coil galvanometer depends inversely on the number of turns of the coil.

Answer 1

The Correct Option is C

To address this problem, we must understand the concepts of current sensitivity and voltage sensitivity of a moving coil galvanometer.

Current Sensitivity (\(S_i\)): It is defined as the deflection (\(\theta\)) per unit current (\(I\)) flowing through the galvanometer. Mathematically, it is given by:

\(S_i = \frac{\theta}{I} = \frac{NBA}{k}\)

where:

• \(N\) = Number of turns of the coil
• \(B\) = Magnetic field strength
• \(A\) = Area of the coil
• \(k\) = Torsional constant of the suspension wire

Voltage Sensitivity (\(S_v\)): It is defined as the deflection per unit voltage (\(V\)) across the coil. It is expressed as:

\(S_v = \frac{\theta}{V} = \frac{NBA}{kR}\)

where:

• \(R\) = Resistance of the galvanometer coil

Conclusion: The percentage change in voltage sensitivity is \(0\%\) since the voltage sensitivity remains unchanged.

Therefore, the correct answer is \(0\%\).