Answer to Question #159619 in Electric Circuits for Keleko

Question

An air-filled capacitor is charged, then disconnected from the power supply, and finally connected to a voltmeter. Explain how and why the potential difference changes when a dielectric is inserted between the plates of the capacitor.
(b) The sum of the charges on both plates of a capacitor is zero. What does the capacitor stote?

Answer 1

(a) The charge of the capacitor will remain the same after it was disconnected from the power supply. The electric field throughout the dielectric would be decreased. Therefore, the potential difference also would be decreased.

(b) Since the sum of the charges on both plates of a capacitor is zero, it means that the plates of the capacitor are equal but oppositely charged. As a result, there is a potential difference between the plates of the capacitor and, hence, there is the energy available to do work. Also, there is an electric field that points from the positive plate to the negative plate. Therefore, the capacitor stores the energy in the form of the electric field between its plates.