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Electricity

It was known to the ancient Greeks as long ago as 600 B.C. that amber, rubbed with wool, acquired the property of attracting light objects. In describing this property today, we say that the amber is electrified (from the Greek, elektron: amber), possesses an electric charge, or is electrically charged. It is possible to put an electric charge on any solid material by rubbing it with any other material (rubbing brings many points of the surfaces into good contact, so that, at the atomic level, electrons are ripped from one material and transferred to the other). Thus, an automobile becomes charged when it moves through the air, a comb is electrified in passing through dry hair, etc.

By the end of the 18th century it was known that electricity comes in two flavors: positive and negative; and that equal charges repel while unequal charges attract. The manner in which this attraction and repulsion occurs was discovered by Coulomb in 1785. He found that the force between them is very similar in form to the gravitational force: it is proportional to the charges of each body, directed along the line joining them, and decreases like the distance squared. There is, however, an important difference: this electric force can be attractive or repulsive; the gravitational force is always attractive.




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next up previous contents
Next: Magnetism Up: Electricity and magnetism Previous: Electricity and magnetism

Jose Wudka
9/24/1998