Sunday, 17 July 2011

Add to order
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.
See Question of the Week #128 for information on using this demonstration to enhance class involvement.
REFERENCES: Available. (PIRA 5A10.10)
Here are some web-based references:

Bill Beaty: The Amateur Scientist pages, good related commentary.

Ron Kurtus: The Triboelectric Series of Materials Causing Static Electricity, with lots of interesting commentary.

Thomas B. Jones, Professor of Electrical Engineering, University of Rochester: Triboelectric Series, shor list with appropriate limiting commentary.

, interesting list with link to the Electrical Discharge Association web page.

EQUIPMENT: Glass rod with silk, hard rubber rod with fur, projection electroscope with bright point source for projection.
SETUP TIME: 10 minutes.

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