Question

A resistance of $900\Omega$ is connected in series with a galvanometer of resistance $100\Omega$. A potential difference of $1V$ produces $300$ division deflection in the galvanometer. The value of figure of merit will be

• A. ${10}^{-2}A/div$
• B. ${10}^{-3}A/div$
• C. ${10}^{-4}A/div$
• D. $1/3\ast {10}^{-5}A/div$

Answer 1

The correct option is D $1/3\ast {10}^{-5}A/div$

Current in the circult $I=\frac{1}{900+100}={10}^{-3}A$
$300$ divisions correspond to ${10}^{-3}A$
$\therefore 1$ division corresponds to $\frac{{10}^{-3}}{300}A=\frac{1}{3}\times {10}^{-5}A$
$\therefore$ figure of merit is $\frac{1}{3}\times {10}^{-5}A$