In the circuit shown, AB is a $10\Omega$ uniform slide wire 50 cm long. ${\epsilon }_1$ is 2V accumulator of negligible internal resistance. $R_1$ and $R_2$ are $15\Omega$ and $5\Omega$respectively. When $K_1$ and $K_2$ are both open, the galvanometer shows no deflection when AJ = 31.25 cm. When $K_1$ and $K_2$ are both closed, the balance length AJ = 5 cm.