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How Does a Van de Graaff Generator Work?

The inner workings of a Van de Graaff generator are revealed!

Announcer: Frostbite Theater presents... Cold Cuts! No baloney!

Joanna and Steve: Just science!

Joanna: Hi! I'm Joanna!

Steve: And I'm Steve!

Joanna: This device is called a Van de Graaff generator. It was created in 1929 by Robert Van de Graaff. Initially, it was created to be a high voltage source for early particle accelerators.

In the next few experiments that Steve and I will be doing, we're going to be using the generator. So, we thought it would be nice if we explained how it worked.

Steve: The Van de Graaff generator looks rather big and looks rather impressive, but it's a fairly simple device. On the front panel, we only have two controls. We have an on and off switch and we have a speed control.

On the inside, there are only a few parts. There's a motor. There's a resistor. There's a speed controller, and the power switch.

The electricity comes in from the power cord, runs through the on and off switch, through the speed control, through this ballast resistor that prevents the motor from running too fast, and then back again into the wall. So when we turn the electricity on, the motor spins, and it makes this belt go round and around.

There's a third wire. It comes in from here and attaches to the case. It's called the ground wire. This literally attaches this device to the ground. The earth is a big reservoir of electrons. We can either grab electrons from the earth or dump electrons into the earth. And the electrons can then travel on this wire mesh to the belt.

You'll notice that we have two different materials here. The pulley has a felt coating on it and the belt itself is rubber. And whether electrons transfer to the belt or from the belt depends on what the two materials are. You'll see when I turn it on again, the belt doesn't slide on the pulley. You don't make static electricity by friction. You make static electricity by having two dissimilar materials in contact with each other and then coming apart. There's a chart known as the triboelectric scale and that will give you a rating of what will happen when two materials touch. You can look-up and see if felt and rubber touch, do electrons go to the rubber or onto the felt.

In any event, we get charges on the belt. The charges ride up the belt and into the dome. Inside the dome, you only have a couple of parts. You have another pulley, which is made out of a different material than the bottom pulley, and another wire mesh that will transfer the charges to the dome.

If I put the dome back together again the electrons will collect on it. Until such a time that they transfer to something else, like me!

Joanna: Thanks for watching! I hope you'll join us again soon for an actual experiment!

Steve: Ouch!

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For questions about this page, please contact Steve Gagnon.