Van De Graaff Generator - Function and Principle - Electrostatics
Channel: Physics Partner
Date: 20/07/2022

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Some insulating materials when separated from the surface of others, leave those surfaces electrically charged, each with the opposite sign of charge and with a high potential difference (p.d.).

A machine to make charges was invented in 1929 by a young American called Van de Graaff. Huge machines, some over 30 m high, based on his ideas have been built to produce extremely high potential differences.

Van de Graaff experiments are all based on the fact that like charges repel.

A Van de Graaff generator pulls electrons from the Earth, moves them along a belt and stores them on the large sphere. These electrons repel each other and try to get as far away from each other as possible, spreading out on the surface of the sphere. The Earth has lots of room for electrons to spread out upon, so electrons will take any available path back to the ground.

The grounding rod is a smaller sphere, attached by a wire to the Earth. It provides a convenient path for electrons to move to the ground. If we bring the grounding rod close enough to the large sphere, the electrons rip through the air molecules in order to jump onto the grounding rod, creating a spark and crackling noise.

When a fluorescent light tube approaches the negatively charged generator, the electrons on the generator flow through the tube and the person holding it. Flowing electrons result in an electrical current, lighting up the light tube. It doesn't take very much current to light a fluorescent bulb!

Putting Styrofoam peanuts or confetti on top of the Van de Graaff generator can create a cool trick. The electrons that collect on the sphere spread out into the Styrofoam peanuts and confetti, making the little, light objects negatively charged. When the negative charges on the peanuts repel the negative charges on the generator, the peanuts push off the sphere.

When a student puts a hand on the sphere, the electrons will spread out onto that person as they repel from the other electrons. They are most obvious in a person's hair because the like charges of the electrons repel each other and cause the hairs to stand up and spread away from each other. As long as the person is standing on an insulated platform, the electrons will not be able to travel down to the ground and their hair will remain standing up.