A parallel-plate capacitor is attached to a fixed voltage supply.If the plates are then separated to double the initial value,what happens to the energy stored by the capacitor?
A)It halves,go figure!
B)It stays the same since the volume doubles while the electric field halves.
C)It doubles since the volume between the plates doubles.
D)It quadruples since both the volume and the field double in this case.

Question

Quizplus · Accepted Answer

The energy stored in a capacitor is given by $ U = \frac{1}{2} C V^2 $. When the plate separation doubles, the capacitance $ C $ halves (since $ C = \frac{\varepsilon A}{d} $), and since the voltage $ V $ is constant, the energy stored halves.

A Parallel-Plate Capacitor Is Attached to a Fixed Voltage Supply