Question

A parallel plate condenser with a dielectric of dielectric constant K between the plates has a capacity C and is charged to a potential V volt. The dielectric slab is slowly removed from between the plates and then reinserted. The net work done by the system in this process is
A. (a) zero
B. (b) `1/2(K-1)CV^2`
C. (c) `(CV^2(K-1))/(K)`
D. (d) `(K-1)CV^2`

Answer 1

Correct Answer - A
The potential energy of a charged capacitor before removing the dielectric slat is `U=(Q^2)/(2C)`.
The potential energy of the capacitor when the dielectric slat is first removed and the reinserted in the gap between the plates is `U=(Q^2)/(2C)`
There is no change in potential energy, therefore work done is zero.