A parallel-plate capacitor with fixed plate area A is initially charged so that the…
PHYSICS · Multi-part · CBSE · Physics · Electrostatic Potential and Capacitance · Electrostatic Potential and Capacitance
Problem
A parallel-plate capacitor with fixed plate area A is initially charged so that the plates carry charges +Q and −Q while separated by a distance d. Immediately after charging, the capacitor is isolated from any external circuit.
Subsequently, an insulating spacer is inserted so that the plate separation increases to 1.50d while the charge on each plate remains unchanged.
(a) Describe qualitatively how the potential difference between the plates changes as the separation increases, assuming no charge is allowed to leave the plates.
(b) Derive an expression for the ratio of the final potential difference to the initial potential difference, ΔViΔVf, in terms of the ratio of plate separations.
(c) Obtain the ratio of the final electric-potential energy stored in the capacitor to the initial energy, UiUf, and interpret your result physically.