Question

A parallel plate capacitor is charged an then disconnected from the charging battery. If the plates are now moved farther apart by pulling at them by means of insulating handles, then

• A. The energy stored in the capacitor decreases
• B. The capacitance of the capacitor increases
• C. The charge on the capacitor decreases
• D. The voltage across the capacitor increases

Answer 1

The correct option is D The voltage across the capacitor increases

When the capacitor is charged and then disconnected, the charge across the plates remains a constant, even when the plates are separated.

The capacitance is related to the structure of parallel plate capacitor as $\frac{A{ϵ}_0}{d}$.

When the plates are separated, the distance between the plates $d$ increases and hence the capacitance decreases.

Hence from $Q=CV$, the voltage across the capacitor increases in order to keep the charge constant.