Question

The deflection in a moving coil galvanometer falls from $50$ divisions to $10$ divisions when a shunt of $12\Omega$ is connected with it. The resistance of galvanometer coil is ?

• A. $12\Omega$
• B. $36\Omega$
• C. $48\Omega$
• D. $24\Omega$

Answer 1

The correct option is C $48\Omega$

Let us denote deflection in galvanometer by $\theta$, in case of a galvanometer, $I\propto \theta$.

Given,

$\frac{I_G}{I}=\frac{10}{50}=\frac{1}{5}$

$\Rightarrow I_G=\frac{1}{5}I$

Now, as in case of a shunted galvanometer as shown in the figure,


$(I-I_G)S=I_{G}G$

$\Rightarrow (I-\frac{1}{5}I)\times 12=\frac{1}{5}IG$

$\Rightarrow G=4\times 12=48\Omega$

Hence, option (d) is correct answer.