question_answer 26)

The plates of a parallel plate capacitor have an area of 90 cm2 each and are separated by 2.5 mm. The capacitor is charged by connecting it to a 400 V supply. (a) How much electrostatic energy is stores 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.  

Answer:

Using                 we get                 = 3.187 × 10?11F                 Work done,                                                 = 2.55 × 10?6J.                 Energy per unit volume,                 U = 0.113 J m?3                 Energy per unit volume,                                 But                                                 Relation between U and E is,