A parallel plate air capacitor has capacity ' $C$ ' and distance of separation between plates is ' $d$ '. If a conducting sheet of thickness $\frac{2 d}{3}$ is inserted in between the plates, the capacitance becomes $C_1$. The ratio of $\frac{C_1}{C}$ is

Initially $n$ identical capacitors are joined in parallel and are charged to potential V. Now they are separated and joined in series. Then

A series combination of 10 capacitors, each of value ' $\mathrm{C}_1$ ' is charged by a source of potential difference ' 4 V '. When another parallel combination of 8 capacitors, each of value ' $\mathrm{C}_2$ ' is charged by a source of potential difference ' V ', it has the same total energy stored in it as in the first combination. The value of ' $\mathrm{C}_2$ ' is

The graph shows the variation of voltage (v) across the plates of two parallel plate capacitos $A$ and $B$ versus increase of charge $Q$ stored in them. Then