5C10.20-Parallel Plate Capacitor


Description: This demo uses a large parallel plate capacitor to show that the capacitance varies when the air gap size is changed.


  • Large Parallel plate capacitor
  • Rods and fur
  • Large Kilovolt potentiometer
  • Two short wires

Setup Procedure:

  1. Connect both wires from the capacitor to the kilovolt meter (grounded wire on insulated plate). The wires should not be touching anything, so use short wires (else a charge won’t stay on the plates).
  2. Test to make sure the plates hold a charge.

Demonstration Procedure:

  1. Start with a large air gap.
  2. Use the fur to charge up the rod. Put the charge on the insulated plate.
  3. Move the plate closer and note that the voltage of the capacitor changes.
  4. To discharge the plates, touch your hand across both.

Note: Works best with less then 50% humidity.

Concept: The idea here is to show that the potential difference in a parallel plate capacitor is linearly proportional to the distance between the plates (V=dQ/εA). The potential should rise as the plates are separated further, and should decrease as they are pushed closer together.