Question

An isolated capacitor with a capacitance $C$ has a potential difference between the plates of $V$, which leaves on each plate a charge $Q$.
A dielectric is then pulled out from in-between the plates, what effect does this have on energy stored in the isolated capacitor?

• A. The energy is increased.
• B. The energy is not affected.
• C. The energy is decreased.
• D. There is not enough information given to answer this question.

Answer 1

The correct option is A The energy is increased.

Capacitance in between the plates is given by

$C=\frac{KA{ϵ}_0}{d}$

Hence the capacitance decreases on removing dielectric from the region between the plates.

When capacitor is isolated, the charge becomes constant. Hence the energy stored in capacitor $\frac{Q^2}{2C}$ increases.