Van de Graaff GeneratorVan de Graaff Generator

GoalsGoals Learn how a Van de Graaff generator Learn how a Van de Graaff generator

works and what it is used forworks and what it is used for Explain demonstration/experiments Explain demonstration/experiments

that involve the Van de Graaff that involve the Van de Graaff generatorgenerator

What is it?What is it? The Van de Graaff generator is a The Van de Graaff generator is a

device that separates electric device that separates electric charges mechanically.charges mechanically.

This produces a high voltage with a This produces a high voltage with a low current.low current.

SafetySafety1.1. Do not allow students to use the Van de Graaff generator Do not allow students to use the Van de Graaff generator

unsupervised. unsupervised. 2.2. People with cardiac pacemakers should never operate the People with cardiac pacemakers should never operate the

generator or come in contact with it. generator or come in contact with it. 3.3. Obviously, we are dealing with high voltage here. Stay Obviously, we are dealing with high voltage here. Stay

about three feet away from the collector while it is about three feet away from the collector while it is charged. charged.

4.4. Always discharge the collector dome between experiments Always discharge the collector dome between experiments and when you are finished. and when you are finished.

5.5. The motor produces a lot of heat that could damage the The motor produces a lot of heat that could damage the belt or the motor itself. Do not run the generator belt or the motor itself. Do not run the generator continuously for long periods of time. continuously for long periods of time.

6.6. Leave the upper and lower combs alone. Leave the upper and lower combs alone. 7.7. Keep the entire device clean and dry. Keep the entire device clean and dry. 8.8. Handle the aluminum parts with care. Handle the aluminum parts with care.

How much voltage?How much voltage? VoltageVoltage is… is…is commonly used as a short is commonly used as a short

name for name for electrical potential differenceelectrical potential difference Which means Which means is a measurement of the is a measurement of the

energy contained within an electric field, or energy contained within an electric field, or an electric circuit, at a given point an electric circuit, at a given point

This VdG generator can produce anywhere This VdG generator can produce anywhere from 10-200 thousand volts (V).from 10-200 thousand volts (V).

It is safe because the current is quite low.It is safe because the current is quite low.

What does it look like What does it look like inside?inside?

Base (Electric motor)

Insulating tube

Metal Sphere

Conveyor belt (rubber)

Metal Combs

How does it work?How does it work? The VdG generator is a charge separator.The VdG generator is a charge separator. When turned on, the belt begins to move, When turned on, the belt begins to move,

picking up negative charges deposited by picking up negative charges deposited by the metal comb at the base.the metal comb at the base.

The belt then transfers the charges to the The belt then transfers the charges to the metal comb at the top of the generator.metal comb at the top of the generator.

The metal comb is attached to the metal The metal comb is attached to the metal sphere and thus transfers the negative sphere and thus transfers the negative charges to the sphere.charges to the sphere.

How is the VdG like the How is the VdG like the cashier’s check out at the cashier’s check out at the

grocery store?grocery store?Think of the groceries as charges.

Base (Electric motor)

Insulating tube

Metal Sphere

What is it used for?What is it used for? Used during early research into radioactivity Used during early research into radioactivity

and atomic structure, used as power source and atomic structure, used as power source for particle accelerators.for particle accelerators.

Still used to power high energy x-ray Still used to power high energy x-ray machinesmachines

Useful in laboratory study of Useful in laboratory study of electrostaticselectrostatics

VdG ExperimentsVdG Experiments1.1. Sparks!Sparks!2.2. Shock LineShock Line3.3. Crazy HairCrazy Hair4.4. Flying CerealFlying Cereal5.5. Light off, light on.Light off, light on.6.6. Flying FurFlying Fur7.7. Anyone for Pie?Anyone for Pie?

QuestionsQuestions1.1. Explain in your own words how the VdG Explain in your own words how the VdG

generator works.generator works.

2. 2. Explain in words and using a diagram how:Explain in words and using a diagram how:a.a. Someone’s hair can stand upSomeone’s hair can stand upb.b. How a shock can occurHow a shock can occurc.c. How something can be repelled by the VdG How something can be repelled by the VdG