Observing the Inverse Square Relationship in Coulomb's Law

The Inverse Square Law in electric force is traditionally demonstrated by the Coulomb Torsion Balance, a fragile device that can be hard for students to use and not often found in physics labs. We present a novel way of observing the inverse square law with common materials from a college physics lab and hardware store, potentially offering a more student friendly and accessible lab. Our apparatus consists of a stationary metal sphere and a conductive foam ball, both of which are placed in proximity to each other and charged by a Van De Graaff Generator. By changing the angle of pendulum, we vary the force between the conductive foam ball and metal sphere and use video analysis to make distance measurements as this occurs. These measurements were entered into our mathematical model to obtain the relationship between force and distance.

This method did not require the charges of the metal sphere or conductive foam ball to be known, and the relationship could be solely found through video analysis. With this design, we were able to confirm the inverse square relationship to a high level of accuracy.