A parallel-plate

Before inserting slab-

We know, capacitance c is given by-

Where,

A= Plate Area

d= separation between the plates,

∈₀ = Permittivity of free space = 8.854 × 10^-12 m^-3 kg^-1 s⁴ A²

Energy stored by the capacitor

where C is the capacitance and V is the applied voltage.

After inserting slab capacitance c is given by-

Where,

A= Plate Area

d= separation between the plates,

∈₀ = Permittivity of free space = 8.854 × 10^-12 m^-3 kg^-1 s⁴ A²

k = dielectric strengthof the material

Also, the final voltage becomes

Energy stored by the capacitor–

where ,

C is the capacitance and V is the applied voltage, k is the dielectric constant of the material

The work done on the system in the process of inserting the slab

= change in energy