A uniform conducting wire $A B$ of length 5 m and resistance $5 \Omega$ is connected as shown in the circuit. If the balancing point is obtained at 3 m from $A$, then the value of $E$ is

In the given circuit, the equivalent resistance between $A$ and $B$ is

The Wheatstone bridge shown in the diagram is balanced. If $P_3$ is the power dissipated by $R_3$ and $P_1$ is the power dissipated by $R_1$, then the ratio $P_3 / P_1$ is

A wire of resistance $2 R$ is stretched such that its length is doubled. Then the increase in its resistance is