The plates of a paralllel plate capacitor have an area of `90 cm^(2)` each and are separated by 2.5mm. The capacitance is charged by connecting it to a 400V supply.
(a) How much electrostatic energy is stored by the capacitor ?
(b) View this energy as stored in the electrostatic field between the plates, and obtain the energy per unit volume (u). Hence arrive at a relation between U and the magnitude of electric field E between the plates.

Explanation

(a) `2.55 xx 10^(-6)` J
(b) `u = 0.113 J m^(-3), u = (1//2) epsilon_(0) E^(2)`