5A50.30 - Van de Graaff Generator
Demonstrate a high voltage electrostatic generator.
Obtain equipment for "Van de Graaff Generator Demo". Place the Van de Graaff generator on a stable cart and connect it to ground by plugging its grounding and power cables into the cart, and connecting the cart to a wall outlet. Using banana cables, connect the discharge globe to the ground using the available connector installed on the base of the Van de Graff generator. Connect the discharge rod to the same ground connector as the discharge globe.
The Van de Graaff generator is a completely self-contained high voltage generator which operates on 105-125 volts AC or DC. The voltages present, although they can be "shocking" to the operator if he/she touches one of the grounded switches on the control panel or an object which is less insulated, are harmless due to the very small current that can be drawn. In fact, the entire output of the machine may be safely discharged to the hand. In order to prevent unexpected shocks, the sphere should always be discharged using the adjustable discharge sphere which is mounted on a stand and which is stored on the shelf next to the Van de Graaff machine. The discharge sphere as well as the ground terminal on the base of the generator should be connected to a water pipe or other good ground. Positive connections can be made via the yellow banana plug at the top of the sphere.
Only operate this demo in a open environment away from sensitive electronics or power boxes. Make sure the discharge globe is ~2" away from the generator. Turn on the Van de Graff and watch the charges jump from the generator to the discharge globe.
If the needle-point discharge rod is used, be sure to NEVER stab the top globe with the needle point probe to avoid the creation of scratches in the top globe. If a scratch is made, the van de graaf will stop working as the scratch becomes an ionization point, which compromizes the ability of the globe to store charge in order to build it up enough to breakdown the air and discharge to the globe.
The Van de Graff generator is a high voltage electrostatic generator which utilizes the triboelectric effect and guass' law (Faraday's Ice Pail) to produce charge on a conductive globe. A dielectric belt made of rubber is looped around two rollers made of differing materials. The top roller, which is inside the conductive globe at top, is made from acrylic plastic, and the bottom roller is made of aluminum. When sharp conductive points come in close contact to charges on a surface an electric field is induced. The induced field results from surface charges remaining static on the dielectric rubber belt, created by friction and surface charge transfer via the triboelectric effect between the disimilar roller materials.