Question

The distance between the plates of two identical parallel plate condenser at identical potentials are halved. In the first, the charges are kept constant while in the second, the potentials are kept constant. The ratio of electrical energy in the 2nd case relative to the first is

(a) 4

(b) 2

(c) 1/4

(d) 1

Answer 1

Correct option (a) 4

Explanation:

Hence on reducing the distance to half the potential energy also get halved U1 ' = U/2

In second case,

Similarly on reducing d/2 U2 ' get doubled U2 ' = 2 U;