An ideal parallel-plate capacitor consists of two parallel plates of area A separated by a distance d. This capacitor is connected to a battery and charged until its plates carry charges +Q and -Q, and
The battery is then disconnected. If the separation between the plates is now doubled, the electrical
Energy stored in the capacitor will
A) quadruple.
B) be cut in fourth.
C) not change.
D) double.
E) be cut in half.

Question

Quizplus · Accepted Answer

When the separation (d) between the plates of a capacitor is doubled, the capacitance (C) is halved since capacitance is inversely proportional to the distance between the plates (C = ε₀A/d). However, since the battery is disconnected, the charge (Q) on the capacitor remains constant. The energy (U) stored in a capacitor is given by U = Q²/(2C). If C is halved, U will double, hence the energy stored in the capacitor doubles.

An Ideal Parallel-Plate Capacitor Consists of Two Parallel Plates of Area