PURPOSE: To demonstrate "charging by friction."
DESCRIPTION: Rubbing silk on a glass rod makes the glass positive and the silk negative. Rubbing fur on a hard rubber rod makes the hard rubber negative and the fur positive. This effect is known as "triboelectricity," from the Greek "tribein," or to rub. The positively charged glass rod and the negatively charged hard rubber rod can then be used (1) simply to illustrate that electrical charge exists using an electroscope or (2) to perform other electrostatics experiments.
In fact, the electron charge is not transferred by "friction" but by contact through the process of quantum mechanical tunneling. The Demonstration Reference File contains a list, known as the "triboelectric series" which indicates the tendency of materials to become either positively or negatively charged when they are rubbed on (contact) each other.
SUGGESTIONS:
EQUIPMENT: Glass rod with silk, hard rubber rod with fur, projection electroscope with bright point source for projection.
SETUP TIME: 5 min.
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