5C20.10-Capacitor with Dielectrics

Watch this Demo

MIT Demo https://www.youtube.com/watch?v=e0n6xLdwaT0

Description: This demo illustrates the effects of a dielectric on a capacitor.


  • Large Parallel plate capacitor
  • Rods and fur
  • Large Kilovolt potentiometer
  • Two short wires
  • Dielectric plate
  • Wood stand
  • (Optional) High voltage battery

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.
  3. Rest the dielectric plate upright on the wood stand (to avoid spilling the liquid inside).

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. (Optional) In place of the rods and fur, you can attach a high voltage battery to the capacitor.
  4. Move the plate closer and note that the voltage of the capacitor increases.
  5. Slide the Dielectric plate in between the two plates. Do not touch the dielectric to the insulated capacitor plate. This works best with a small air gap. This increases the capacitance. Since the amount of charge is constant and the dielectric increases the capacitance, then the voltage must decrease (q=C*V).
  6. If using a high voltage battery, when inserting the dielectric the voltage remains constant and extra charge builds up on the plates.
  7. To discharge the plates, touch your hand across both.

Note: The dielectric cannot touch the insulated side.
For best effect, have the plates close to each other for a noticeable difference. High humidity makes it difficult for the plates to hold charge.