The galvanometer deflection, when key $K_1$ is closed but $K_2$ is open, equal $\theta_0$ (see figure). On closing $K_2$ also and adjusting $R_2$ to $5 \Omega$, the deflection in galvanometer becomes $\frac{\theta_0}{5}$. The resistance of the galvanometer is, then given by [Neglect the internal resistance of battery]