A parallel plate capacitor has a uniform electric field '' in the space between the plates. If the distance between the plates is ‘d’ and the area of each plate is ‘A’, the energy stored in the capacitor is : (ε₀ = permittivity of free space)

CONCEPT:

The energy stored in the capacitor is defined as the product of the capacitance and square of the electric potential. It is written as:

Where C is the capacitance of the capacitor and V is the electric potential.

CALCULATION: 

Given that the capacitor has a uniform electric field  and 'd' is the distance between the plates and 'A' is the area and is shown in the figure below;

The energy stored in the capacitor is defined as the product of the capacitance and square of the electric potential. Using equation (1) we have;

 ----(1)

and, the capacitance of a capacitor is written as;

and electric potential,

V = Ed

Now, on putting the value of "C" and "V" in equation (1) we get;

⇒ 

⇒ 

Hence, option 4) is the correct answer.