Man's physical universe

xanabras

UNIT VII

SECTION 2

STATIC ELECTRIC CHARGES MAY BE PRODUCED BY

FRICTION OR INDUCED BY AN ADJACENT CHARGED

BODY

Introduction.

A type of repulsion and attraction between bodies at a distance,

which in some ways resembles the attraction and repulsion of magnetic

poles, is that between electrified bodies. Electric charges may be

produced by friction between surfaces. Unless the air is fairly dry,

these charges will not accumulate to a point where they will produce

striking effects, because films of moisture enable them to be conducted

away. There are many well-known examples of electrification by friction.

Many people, having shufifled across a rug on a dry day, have

produced an electric spark as they touched their fingers to an iron bed,

a radiator, water pipe, or any other metallic object. The electric

charge in this case is produced by the sliding contact between the

shoes and the rug. This effect is more pronounced when the atmosphere

is dry than when it is humid. The crackling and standing on end of dry

hair when a comb is drawn through it is a common experience. Explosions

have resulted from the spark produced by the friction of gasoline

flowing through a pipe, and special precautions are now taken to prevent

such explosions.

Static charges may be produced by friction or they may be induced

by a nearby charged body. An induced charge is the charge acquired

by a neutral body when it is brought near a charged body. The explanation

of this phenomenon will be given later.

There seems to be very little connection between magnetism and

static electricity except that both are related to current electricity.

The great value of a knowledge of static electricity lies in the fact

that it forms a necessary foundation for the understanding of current

electricity.

Static Phenomena Have Been Known for a Long Time.

Thales (640-560 B.C.) discovered that amber, when rubbed with a

woolen cloth, acquired the power to attract to itself light objects such

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