A point charge 'Q' is placed at the centre of the line joining two equal charges '+q' and '+q'. The value of 'Q' when the system is in equilibrium is

Capacitors of capacities $C_1$ and $C_2$ are connected in series. If the combination is connected to a supply of V volt then the potential difference across capacitor $C_2$ is

Two parallel plate air capacitors are connected in parallel. Each capacitor has plate area $A/2$ and separation between the plates is $d$ and $2d$ respectively. The equivalent capacity of the combination is

( $\epsilon_0$ = absolute permittivity of free space)

In metre bridge experiment, the resistance in the left gap is 15 $\Omega$ and in the right gap is 45 $\Omega$. The bridge is balanced. The distance of the null point from the centre of the wire is