In a Wheatstone's network P R , the reading of the galvanometer is the same with a switch 'S' open or closed. Then

Step-by-step solution

When the switch S is open, the resistor R and the galvanometer G are connected in series in the lower branch. Thus, the same current flows through both, giving I_R = I_G . The galvanometer reading remains the same whether the switch is open or closed. This indicates that closing the switch does not alter the current in the galvanometer branch. This condition occurs only if the potential difference across the switch is zero, which means the Wheatstone network is balanced ( P R = Q G ). Since the bridge is balanced,