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

If the masses of three wires of same material are in the ratio of $1: 2: 3$ and their lengths are in the ratio of $3: 2: 1$, then electrical resistances of these wires are in the ratio