The galvanometer deflection, when key K_1 is closed but K_2 is open, equals θ_0 (see figure). On closing K_2 also and adjusting R_2 to 5 Ω, the…

The galvanometer deflection, when key $\displaystyle \mathrm{K}_1$ is closed but $\displaystyle \mathrm{K}_2$ is open, equals $\displaystyle \theta_0$ (see figure). On closing $\displaystyle \mathrm{K}_2$ also and adjusting $\displaystyle \mathrm{R}_2$ to $\displaystyle 5 \Omega$, the deflection in galvanometer becomes $\displaystyle \frac{\theta_0}{5}$. The resistance of the galvanometer is, then, given by [Neglect the internal resistance of battery] :