5A10.20-Electrophorus
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Description: Demonstrates charging by induction.
Equipment:
- Electrophorus wax base
- Aluminum plate with insulated handle
- Fur
- Florescent lights
Demonstration Procedure:
- Rub the fur on the wax base to charge it.
- Turn off the room lights.
- Place the neutral plate close above the wax base.
- Tap the florescent light to the top of the plate.
- Lift up the plate and tap the florescent light to the top of the plate again.
- Place the aluminum plate back above the wax base and repeat steps 4 and 5.
Tips: Always hold the aluminum plate by the insulated handle. This demo works best in low humidity with all the lights off.
Concept: The wax plate is charged by friction by the fur. This gives the wax a net negative charge. When the neutral aluminum plate is brought close to the wax, it becomes polarized. The negative charges on the plate are repelled by the negative charges on the wax so they collect on the top of the plate. The positive charges on the plate are attracted to the negative charges on the wax so they collect on the bottom of the plate. When a fluorescent light touches the top of the aluminum plate, the negative charges flow into it. This leaves the aluminum plate positively charged. The plate has just been charged by induction. Touching the plate again with the fluorescent bulb discharges the plate. The aluminum plate returns to a neutral state.