A parallel plate capacitor is charged to voltage V and then disconnected from the battery. Leopold says that the voltage will decrease if the plates are pulled apart. Gerhardt says that the voltage will remain the same. Which one, if either, is correct, and why?
A) Gerhardt, because the maximum voltage is determined by the battery.
B) Gerhardt, because the charge per unit area on the plates does not change.
C) Leopold, because charge is transferred from one plate to the other when the plates are separated.
D) Leopold, because the force each plate exerts on the other decreases when the plates are pulled apart.
E) Neither, because the voltage increases when the plates are pulled apart.

Question

Quizplus · Accepted Answer

When the plates of a disconnected parallel plate capacitor are pulled apart, the capacitance decreases because capacitance is inversely proportional to the distance between the plates (C = εA/d, where A is the area of the plates, d is the distance between them, and ε is the permittivity of the medium between the plates). Since the charge (Q) on the capacitor remains constant (because it's disconnected from the battery), and the voltage (V) across a capacitor is given by V = Q/C, if C decreases, V must increase.

A Parallel Plate Capacitor Is Charged to Voltage V and Then