In the circuit shown the cells A and B have negligible resistances. For VA = 12 V, R1 = 500 $\Omega $ and R = 100 $\Omega $ the galvanometer (G) shows no deflection. The value of Vs is

Question

In the circuit shown the cells A and B have negligible resistances. For V_A = 12 V, R₁ = 500 $\Omega $ and R = 100 $\Omega $ the galvanometer (G) shows no deflection. The value of V_s is