Description: This demo illustrates the effects of a dielectric on a capacitor.
Equipment:
- Large Parallel plate capacitor
- Rods and fur
- Large Kilovolt potentiometer
- Two short wires
- Dielectric plate
- Wood stand
- (Optional) High voltage battery
Setup Procedure:
- 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).
- Test to make sure the plates hold a charge.
- Rest the dielectric plate upright on the wood stand (to avoid spilling the liquid inside).
Demonstration Procedure:
- Start with a large air gap.
- Use the fur to charge up the rod. Put the charge on the insulated plate.
- (Optional) In place of the rods and fur, you can attach a high voltage battery to the capacitor.
- Move the plate closer and note that the voltage of the capacitor increases.
- 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).
- If using a high voltage battery, when inserting the dielectric the voltage remains constant and extra charge builds up on the plates.
- 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.