Source: Yong P. Chen, PhD, Department of Physics & Astronomy, College of Science, Purdue University, West Lafayette, IN

This experiment will use commercial capacitors and a parallel plate capacitor to demonstrate the concept of capacitance. A capacitor stores opposite charges on two conductors, for example two opposite metal plates, leading to a potential difference (voltage drop) between the two conductors. The amount of charge on each conductor is proportional to this voltage drop, with the capacitance as the proportionality factor. If the voltage is changing with time, the current flowing into the capacitor will be proportional to the rate of that change, and again the capacitance is the proportionality factor.

The capacitance of the parallel plate capacitor is the product of the dielectric constant with the distance between the plates divided by the area of the plate. This experiment will demonstrate the proportionality with distance by first depositing some charge onto the capacitor and then using a high-impedance voltmeter (electrometer) to monitor the voltage between the plates as the distance is increased. The voltage change will also be monitored with a dielectric material, such as a plastic plate inserted into the space between the metal plates.

A capacitance meter will be used to directly measure the capacitance, as well as to measure parallel and series connections of commercially-available capacitors and to study how the total capacitance is related to individual capacitances.