demonstrations:van_de_graaff_pie_tins

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

  1. Place the Van de Graaff generator in an open space with enough room above for the plates to fly off.
  2. Plug in the generator and grounding rod.
  3. Stack 5 or more small aluminum pie plates upside down on the dome of the generator.
  4. Use the grounding rod to switch on the generator and step back.
  5. Watch as the plates charge, repel each other, and fly off one by one.
  6. When all plates have discharged, use the grounding rod to safely turn off and discharge the generator.

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?