Question

Deduce the expression for electrostatic
energy stored in capacitor having
Charge Q. How will the energy stored
and electric field inside capacitor
be affected when it is completely
filled with a dielectric material
of dielectric constant k?​

Answer 1

Capacitance and Electrostatic Potential :

On introduction of dielectric material,

Capacitance, C = $\epsilon{_0}$ A / d

C' = K $\epsilon{_0}$ A/ d

( i ). Electric field lines are shown in figure.

( ii ). Energy stored, U = q^2 / 2C '

Energy stored later , U' = q^2 / 2KC

U' = 1/K ( q^2/ 2C)

U' = 1( U ) / K

U' = 1 × U / K

Hence, Stored energy decreases and becomes 1/K times of the original energy.