Question

If e is the electric field intensity of an electrostatic field then the electrostatic energy density is proportional to

1)e

2)e×e

3)1/e×e

4)e×e×e

Answer is 2

Answer 1

We know that, for a capacitor,
U = ½CV²
Here, C = EoA/d and V = Ed
Therefore, U = ½(EoA/d)*(Ed)²
or, U = ½EoE²V (where V=Ad)
Hence the required expression for the energy density of a parallel plate capacitor is given by
U/V = ½EoE²
Electrostatic energy density
U/V∝E²