Van de Graaff Generator

A Van de Graaff generator is a device which produces and stores a large electrostatic charge on a metal dome. It is designed to create static electricity and make it available for experimentation. The American physicist Robert Jemison Van de Graaff invented the Van de Graaff generator in 1931.

Safety 1.Do not allow students to use the Van de Graaff generator unsupervised. 2.People with cardiac pacemakers should never operate the generator or come in contact with it. 3.Stay about three feet away from the collector while it is charged. 4.Always discharge the collector dome between experiments and when you are finished. 5.The motor produces a lot of heat that could damage the belt or the motor itself. Do not run the generator continuously for long periods of time. 6.Keep the entire device clean and dry. 7.Handle the aluminum parts with care. 8. Though the Van de Graaff operates at high voltage, its low current assures that it is HARMLESS. Nevertheless, a shock from it can be quite unpleasant.

How does Van de Graaff Generator Work? The Van deGraaff generator is a charge separator. The basic fundamental principle behind this apparatus is separating opposite charges at both ends of the rubber belt. When turned on, the belt begins to move, picking up positive charges deposited by the metal comb at the base. The belt then transfers the charges to the metal comb at the top of the generator. The metal comb is attached to the metal sphere and transfers the positive charges to the sphere.

Triboelectric Series How strongly material holds on to its electrons determines its place in the triboelectric series. If a material is more prone to give up electrons when in contact with another material, it is more positive in the triboelectric series. If a material is more prone to "capture" electrons when in contact with another material, it is more negative in the triboelectric series. When materials are rubbed onto each other, the charge is generated through friction. In the table below, rubbing any material in the list with any material below it will cause the upper material to become positively charged. For example rubbing Teflon on rubber will produce a negative charge on Teflon and a positive charge on the rubber. The farther apart the materials are in the list, the greater the charge will be. Triboelectric series Positive Rabbit's Fur Glass Human Hair Nylon Wool Cat's Fur Silk Aluminum Paper Cotton Polystyrene Polyethylene Rubber balloon Hard rubber Polyester Polyurethane Polyethylene Polypropylene Vinyl Teflon Saran Wrap PVC Negative

Schematic view of Van de Graaff Generator 1)hollow metal sphere (collector) 2) upper brush 3) upper roller (for example, an acrylic glass) 4) side of the belt with positive charges 5) opposite side of the belt with negative charges 6) lower roller (for example, Teflon) 7) lower brush 8) discharge bell 9) spark 10) motor