Concepts

Electrostatics, triboelectricity, dielectric breakdown

Overview

Static charge builds up on the Van de Graaff generator dome. Many different individual demos can be done with it. The Van de Graaff can be used to charge up the hair of a Barbie doll or person. When tart pans or rice krispies are charged up, they rain down on the ground one by one. Fluorescent lights will flash when sparked by the generator. A grounded dome or discharge wand can demonstrate dielectric breakdown in air.

As with all electrostatic experiments, unless conditions are ideal (dry, cold), the demonstration may perform worse than expected.

Details

Equipment

• [1] Van de Graaff generator
• [1] Discharge wand
• [1] Barbie doll
• [1] Plastic step stool
• [1] Mirror
• [10] Tart pan
• [1] Grounded tower
• [1] Ornament on a stick
• [1] Fluorescent light with attached banana cable and clip
• [1] Leiden jar and wand
• [1] Semiconductor and pin
• [1] Flashlight
• [1] Extension cord

Classroom Assembly

1. Put the Van de Graaff somewhere away from computers and plug it in.

Important Notes

• People with pacemakers, insulin pumps, cochlear implants, or other critical devices should not come near the Van de Graaff.
• Ensure the Van de Graaff is not near any computers or other electronics, such as phones.
  
• People being charged on the Van de Graaff should not touch the dome again after letting go.
• For the demo of charging someone's hair, try to pick someone with shoulder-length hair.
• When transporting the Van de Graaff on a bumpy path, the plexiglass casing and attached belt mount can rotate, twisting the belt. Be sure to straighten that out before use.
• Test the Van de Graaff just before show time to avoid untimely failures.

Script

Barbie or tart pans

1. Place Barbie or tart pans on top of the dome. Tart pans should have the open part facing down.
2. Turn on the Van de Graaff generator. Barbie's hair should flare out or the tart pans should fly off.
3. While grounding the Van de Graaff, turn it off.

Person

1. Get the volunteer to stand on the step stool, putting one hand on the Van de Graaff dome.
2. Tell the volunteer to not touch the dome again if she or he lets go.
3. Start the generator.
4. Tell the volunteer to shake one's head.
5. Show the volunteer what he or she looks like in the mirror.
6. Use just the grounded banana cable (not the grounding rod) to make the volunteer's hair dance by bringing the end of the cable close to the dome, then away, then close, and so on.
7. Tell the volunteer to let go of the Van de Graaff and turn it off.
8. Note how the volunteer's hair is still standing up.
9. Tell her or him to jump off the stool, and most of the charge should drain away. Alternatively, tell the volunteer discharge by elbowing the elbow of another volunteer standing on the ground, then jumping off the stool.

Chain of pain (zap several people)

1. Get a few volunteers.
2. Everyone except the one standing on the stool and touching the Van de Graaff should link hands or pinkies. The last one in the chain should be touching a grounded object, like a faucet, if possible.
3. Start the Van de Graaff generator.
4. The person touching the Van de Graaff should make elbow-to-elbow contact with the next person on the chain.
5. Stop the Van de Graaff generator.

Fluorescent light

1. Ground the light by plugging the banana cable into the grounding port on the Van de Graaff generator.
2. Start the generator.
3. Bring the fluorescent light closer to the generator. Further from the dome, the light will periodically illuminate from relatively large sparks. Close to the dome, the light will almost continuously illuminate from many small sparks.
4. Ground the generator and turn it off.

Dielectric breakdown

1. Set up the grounded tower next to the Van de Graaff generator, with grounding wire plugged in to the generator's grounding port.
2. Start the Van de Graaff.
3. Vary the distance between the Van de Graaff and the grounded tower as required.
4. Ground the Van de Graaff and turn it off.

Oscillating ornament

1. Set up the grounded tower 20–30 cm from the Van de Graaff generator, with grounding wire plugged in to the generator's grounding port.
2. Start the Van de Graaff.
3. Place the ornament on a stick such that the ornament is suspended between the Van de Graaff and grounded tower.
4. Adjust the ornament's string length or position until the ornament oscillates.
5. Ground the Van de Graaff and turn it off.

Additional Resources