Goals • Learn how a Van de Graaff generator works and what it is used for • Explain demonstration/experiments that involve the Van de Graaff generator
What is it? • The Van de Graaff generator is a device that separates electric charges mechanically. • This produces a high voltage with a low current.
Safety • Do not allow students to use the Van de Graaff generator unsupervised. • People with cardiac pacemakers should never operate the generator or come in contact with it. • Obviously, we are dealing with high voltage here. Stay about three feet away from the collector while it is charged. • Always discharge the collector dome between experiments and when you are finished. • 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. • Leave the upper and lower combs alone. • Keep the entire device clean and dry. • Handle the aluminum parts with care.
How much voltage? • Voltage is…is commonly used as a short name for electrical potential difference • Which means is a measurement of the energy contained within an electric field, or an electric circuit, at a given point • This VdG generator can produce anywhere from 10-200 thousand volts (V). • It is safe because the current is quite low.
What does it look like inside? Metal Sphere Insulating tube Conveyor belt (rubber) Metal Combs Base (Electric motor)
How does it work? • The VdG generator is a charge separator. • When turned on, the belt begins to move, picking up negative 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 thus transfers the negative charges to the sphere.
How is the VdG like the cashier’s check out at the grocery store? Think of the groceries as charges.
Metal Sphere Insulating tube Base (Electric motor)
What is it used for? • Used during early research into radioactivity and atomic structure, used as power source for particle accelerators. • Still used to power high energy x-ray machines • Useful in laboratory study of electrostatics
VdG Experiments • Sparks! • Shock Line • Crazy Hair • Flying Cereal • Light off, light on. • Flying Fur • Anyone for Pie?
Questions • Explain in your own words how the VdG generator works. 2. Explain in words and using a diagram how: • Someone’s hair can stand up • How a shock can occur • How something can be repelled by the VdG