Van de Graaff Pie Tins
Materials: ★★☆ Available in most school laboratories or specialist stores
Difficulty: ★★☆ Can be done by science teachers
Safety: ★★★ Only to be attempted with adequate safety procedures and trained staff
Categories: Electricity, Van de Graaff Generator
Alternative titles: Floating Pie Plates, Van de Graaff Coulomb Repulsion
Summary
A stack of aluminum pie plates placed on top of a Van de Graaff generator’s dome will charge and repel each other. As the generator accumulates charge, the plates lift off one by one, demonstrating that like charges repel.
Procedure
- Place the Van de Graaff generator in an open space with enough room above for the plates to fly off.
- Plug in the generator and grounding rod.
- Stack 5 or more small aluminum pie plates upside down on the dome of the generator.
- Use the grounding rod to switch on the generator and step back.
- Watch as the plates charge, repel each other, and fly off one by one.
- When all plates have discharged, use the grounding rod to safely turn off and discharge the generator.
Links
Why Do Pie Plates Fly Off a Van de Graaff Generator? (Physics Demo) - Phantastic Physics:
📄 Putting Pie Plates on a Van De Graaff Generator - Classroom Physics Demos: https://demos.smu.ca/demos/e-n-m/53-pie-plates
Variations
- Use different sizes of pie plates to compare how mass affects the speed and height of lift-off.
- Try lightweight foil trays or other conductive objects.
- Place a lightweight toy (like a rubber duck) on top of the plates for added visual effect.
- Record in slow motion to observe the instant each plate becomes charged and separates.
Safety Precautions
- Always use the grounding rod to switch the generator on and off.
- Discharge the dome after use with the grounding rod.
- Stand back while plates are flying to avoid accidental hits.
- Do not operate near sensitive electronic devices.
Questions to Consider
- Why do the pie plates repel each other instead of staying stacked?
- What role does conduction play in transferring charge from the dome to the plates?
- Why do lighter plates fly off more easily than heavier ones?
- How does this demonstration model the way charge distributes itself on conductors?
- In what ways is this similar to the sparks and hair-raising Van de Graaff demonstrations?