Question

To increase the current sensitivity of a moving coil galvanometer by $30$ %, its resistance is increased so that the new resistance becomes thrice its initial resistance. Calculate the factor by which the voltage sensitivity change.

• A. Decreases by $57\%$
• B. Increases by $57\%$
• C. Decreases by $37\%$
• D. Decreases by $27\%$

Answer 1

The correct option is A Decreases by $57\%$

We know that,

$V_s=\frac{I_s}{R}$

When current sensitivity is increased by $30\%$ and resistance is made three times, then,

$V_s^{\prime }=\frac{I_s+0.3I_s}{3R}=\frac{1.3I_s}{3R}=0.43V_s$

So,

$\frac{V_s-V_s^{\prime }}{V_s}\times 100=\frac{V_s-0.43V_s}{V_s}\times 100=57\%$

Thus, the voltage sensitivity decreases by $57\%$.