Each plate of a parallel -plate air capacitor has an area `S`. What amount of work has to be performed to slowly increases teh distance between the plates from `x_(1)` to `x_(2)` if
(a) Capacitance of the capacitor which is equal to `q`, or (b) the voltage across the capacitor, which is equal to `V`, is kept constant in the process?

Answer

`(i) (q^(2)(x_(2)-X_(1)))/(2in_(0)S)`
(ii) `(-)(in_(0)SV^(2)((1)/(x_(2))-(1)/(x_(1))))/(2)`