Demos: 5A-04 Insulators and Conductors

A pair of ping-pong balls is coated with conductive paint and suspended by long, light conductive rods from a metal plate. The plate is supported by an insulating stand. The metal plate is connected to an electrostatic generator and when the generator is turned on, the coated balls repel each other. The demonstration is repeated, but with the conducting rods replaced by insulating rods. The balls are only slightly deflected, primarily from charge leakage on the rods. The demonstration shows that charges are more readily transferred by conductors.

Directions: The insulating suspension rods should be cleaned prior to the demonstration to reduce the amount of charge leakage. Connect the lead(s) from the generator to the metal plate and turn the generator on. The “speed” of the generator can be adjusted to produce the proper deflection.

Suggestions for Presentation: An effective way to introduce the concept of conductors and insulators is to perform the first part of the demonstration (conducting rods) and note the deflection. Discuss the reasons for this happening. (The balls clearly must be charged with like charges.) Then repeat the demo with the insulating rods and note the small deflection. Ask what this implies.

Applications: The most obvious applications are the use of insulators and conductors in electrical wiring, for example. Point out the role of each.

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