Get an electrostatic hairdo in this classic demonstration!
Teachable Topics:
- Van de Graaff Generator
- Electric charge
Theory:
A Van de Graaff (VDG) generator is a machine that continually draws electrons off a large metal dome. The dome thus becomes strongly positively charged once the machine is turned on. If an object touches the dome on this machine, that object also becomes positively charged because some of the electrons from the object are drawn to the positively-charged dome.
Figure 1: Illustration of how a Van der Graaf Generator works
Charges with the same sign repel one another. If a person touches the VDG, the person's body becomes positively charged. All the hairs on the person then begin to repel one another. To spread as far apart as possible, the hairs then stand up, as seen in the video below.
Apparatus:
- a Van de Graaff Generator
- a wooden chair
- a wooden stick (such as a meter stick)
- a volunteer
Procedure:
- Set the Van de Graaff generator on a table and place the wooden chair a few feet from it.
- Have someone sit or stand on the chair with his/her feet off the ground and the generator off.
- Get the volunteer to place his/her hands on the Van de Graaff.
- Flip the switch, and watch the person's hair stand on end! (People with medium to long, fine hair make the best volunteers.
- After the demo is finished, switch the generator off, then touch the volunteer with the wooden stick to draw off the remaining electric charge.
SAFETY WARNINGS:
- Make sure the Van de Graaff Generator is turned off before anyone touches it, otherwise the person risks getting shocked.
- Shocks through fingers and toes hurt the most. If you must discharge yourself without using the wooden stick, it's best to use a bent knuckle.
- Use the grounding rod to turn the generator on and off. After it is shut off, touch the rod to the to of the generator to remove any risidual charge.
