Physics Demo Number: 195
Approximate
Run Time: 5 min
Electrophorus
Demo Description
A plate of teflon sits on insulated feet.
One rubs the white teflon plate with fur to give it a negative charge.
Subsequent placing of a round metal plate on the teflon plate allows for charging the metal plate by induction.
Scientific Principles
Charging by induction.
Properties of insulators versus conductors at a visual level.
Equipment
- Electrophorus.
- Small light tube.
- Rabbit fur.
Equipment Location
- Kit 195 on [B-3-5]
Instructions
The photo shows the Electrophorus, which consists of
- a black and tan base
- a white teflon plate ( which is attached to the base by nylon screws )
- a round metal plate with an insulating black handle attached to it.
- a piece of fur for rubbing on the teflon to charge it
- a tube light for showing accumulated net charges.
When the teflon plate is charged, one may put the metal plate down on it ( while holding the plate by the insulating handle ) and momentarily touch a thumb to the plate.
The result of the momentary touch of the thumb should be a strong spark jumping between the plate and the thumb.
If a tube light is laying near the plate, the spark from the plate to the thumb will cause a momentary flash in that light tube ( refer to Hertz's experiment #(155) for a possible complementary insight for your class).
One may pick up a light tube and touch it to the charged plate to see a flash of light.
One may touch the tube straight to the teflon plate with no flash, since teflon is a very good insulator.