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
- 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 charge won’t stay on the plates).
- Test to make sure the plates hold a charge.
- Start with a large air gap.
- Rub the fur on the rod, and the touch the rod on the insulated plate.
- Move the plate closer and note that the voltage of the capacitor changes.
- To discharge the plates, touch your hand across them.
Note: Works best with less then 50% humidity.
Concept: This demo shows 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.