Van De Graaff Generator Wonders

Objectives

• Explain how static charge causes materials to attract or repel each other.

Materials

• Per Class or Group:
  A Van de Graaff Generator (available at Arbor Scientific)
  a plastic stool
  Styrofoam peanuts (or confetti)
  metal pie pan
  a mirror

Key Questions

• Where are the electrons?
• What is making your hair stand on end?
• Why doesn’t the hair come down after the machine has been turned off?
• What caused a shock when the volunteer touched a fellow student?
• Why did your teacher ground the generator before allowing the volunteer to step off the stool?
• What is the role of the plastic stool?

What To Do

Safety note: Make sure you ground the large sphere after each use by touching it with the ground wire or small sphere. Although the Van de Graaff generator produces a very low current, it may cause problems with people who have heart problems or a pacemaker. Warn students they may get small shocks which will scare them more than hurt them.

Part 1: Making Sparks

1. Touch the small sphere (connected to the ground wire) to the dome.
2. Turn the knob counter clockwise.
3. Turn the generator on.
4. Slowly turn the knob clockwise so the motor turns the belt.
5. Take the small sphere away and let a charge accumulate on the dome. Ask a student to turn off the lights to make it easier to see the sparks.
6. Move the small sphere around the sphere in different positions so that everyone can see the sparks.

Part 2: Sautéing Styrofoam 

1. Ground the dome by touching the grounding rod to it.
2. Without removing the grounding rod, place Styrofoam peanuts (or confetti) on top of the large sphere.
3. Take the ground away, and the Styrofoam peanuts will fly off the generator.
4. This can be repeated by placing a metal pie panplate (or three!) on top of the generator and repeating the steps above.

Part 3: Hair-Raising Experience

1. Ask a student to step up onto the insulated stool.
2. Ground the dome by touching the grounding rod to it.
3. Without removing the grounding rod, ask the volunteer to put one hand on the dome, the other hand by their side and make sure they understand not to move their hands until you tell them to.
4. Take the ground away, and their hair will start to stand up. Shaking their head will help too!
5. Hold the mirror so that the volunteer can see their new hair-do!
6. Ask the volunteer to move their hand from the ball to their side, and to keep it there. Immediately ground the Van de Graaffand then turn it off.
7. The volunteer can simply step off the stool or touch elbows with a classmate to get rid of their extra electrons (note: touching elbows will result in a shock!).

Extensions

• Place a piece of fake fur on the large sphere, the individual fur strands will stand.
• Tape streamers to your volunteer, like an extra-long moustache!
• Have someone hold onto the large sphere while blowing soap bubbles with a wand, the bubbles will become positively charged and will be attracted to anything that is grounded e.g. a person walking by.
• A fly stick is a miniature, battery powered Van de Graaff generator. It charges mylar objects, which are then repelled by the stick (and by each other). You can make small objects hop up and down between the stick and your hand or levitate the more visible ones. For fun ideas, check out the Educational Innovations' teacher blog.