Van de Graaff Generator

Dionna Dunning, Paulinho Smith and Tiffany Dooley

Dionna, Paulinho and Tiffany with their Van de Graaff Generator

The objective of this project was to make a Van de Graaff generator that was large enough for classroom demonstrations, but portable. Van de Graaff generators develop high voltages by depositing charge on a metal sphere. A motor in the base turns a belt that wraps around a pulley near the top. A roller on the end of the motor shaft and the belt are both made of materials that are good insulators. The belt and shaft materials occupy different locations in the triboelectric series; so when the belt pulls away from the shaft, it carries extra electrons with it. These electrons are carried on the insulating belt to the top pulley where they are collected by a metal brush and stored on a metal sphere. As the belt continues to rotate, more electrons collect on the metal sphere until its voltage is raised to the point where it will accept no more charge.

In this design, the belt was made of teflon and the motor shaft was covered with a nylon roller. The base was made of plexiglass allowing students to view the motor, nylon roller and belt. The brushes were copper and the sphere was stainless steel. The metal sphere and upper pulley were supported by a PVC pipe.

The final version of the Van de Graaff generator was capable of producing sparks a few inches long when discharging to a person's extended hand. The sparks were clearly audible and visible in a darkened classroom. It could also make a person's hair stand on end when the person was well insulated from the ground and holding their hand on the sphere.