Van de Graaff generator.

Van de Graaff generator. This Van de Graaff apparatus is an electrostatic generator capable of throwing sparks 25 to 38 cm. long from the primary electrode to a secondary discharge electrode (depending on humidity, motor speed,etc.) The apparatus is safe, delivering at most a 10 microamp current. A large hollow conducting aluminum sphere is supported on top of a tall insulating lucite column above a metal base. The sphere is charged to a high potential (250K-400K volts) by a moving nonconducting rubber belt. In the base, the felt-covered roller, pressing against and separating from the rubber belt, causes negative charge to be left on the rubber belt as it travels upward. When the belt reaches the top and rolls over the lucite roller, the negative charge jumps to sharp collector points and is transferred immediately to the outer surface of the metal sphere. As more charge is brought upward, the sphere becomes more highly charged and reaches greater voltage. The process requires energy, since the upward moving charged belt is repelled by the charged sphere. The energy is supplied by the motor driving the belt.
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The hand crank van de graaff is very light, you may want to clamp it. If you're using it to charge a person then you can slowly uncharge them by having them grab ahold of a wooden meter stick and moving their hand back and forth on it. The charge will dissipate slowly enough that there should be no shock. As always when you present a demo make sure you ask the participants questions before you demonstrate and after. Think about the concepts involved beforehand; having a friend ask you questions about it can be very revealing as to if you understand it well or not. Whenever you ask a question count to five (or at least three) in your head waiting for an answer before you stay anything else.