Question

The figure shows two identical parallel plate capacitors connected to a battery with the switch S closed. The switch is now opened and the free space between the plates of the capacitors is filled with a dielectric of dielectric constant (or relative permittivity) 3. Find the ratio of the total electrostatic enegry stored in both capacitors before and after the introduction of the dielectric.

Answer 1

Before opening the switch potential difference across both the capacitors is V, as they are in parallel. Hence, energy stored in them is,

After opening the switch, potential difference across it is V and its capacity is 3C

In case of capacitor B, charge stored in it is q = CV and its capacity is also 3C.