When a resistance of $200 \Omega$ is connected in series with a galvanometer of resistance ' $G$ ', its…
When a resistance of $200 \Omega$ is connected in series with a galvanometer of resistance ' $G$ ', its range is ' V '. To triple its range, a resistance of $2000 \Omega$ is connected in series. The value of ' $G$ ' is
$200 \Omega$
$400 \Omega$
$600 \Omega$
$700 \Omega$
Solution
Using, $R_s=\frac{V}{I_g}-G$ we get, for $1_1^{\text {st }}$ case, $200=\frac{\mathrm{V}}{\mathrm{I}_{\mathrm{g}}}-\mathrm{R}$
....(i) and for $2^{\text {nd }}$ case, $2000=\frac{3 \mathrm{~V}}{\mathrm{I}_{\mathrm{g}}}-\mathrm{R}$...(ii)
By subtracting equation (i) from (ii) we get,
$\begin{array}{ll}
& \frac{\mathrm{V}}{\mathrm{I}_{\mathrm{g}}}=900 \\
\therefore \quad & \mathrm{R}=700 \Omega
\end{array}$