The potential difference across the 4 capacitor in the following circuit is

A capacitor of unknown capacity is connected across a battery of V volt. The charge stored in it is Q coulomb. When potential across the capacitor is reduced by $\mathrm{V}_1$ volt, the charge stored in it becomes $\mathrm{Q}_1$ coulomb. The potential V is

Five capacitors, each of capacitance ' $C$ ' are connected as shown in the figure. The ratio of equivalent capacitance between P and R and the equivalent capacitance between P and Q is

The function of a dielectric in a capacitor is