Electroscope

Electroscope

An instrument for detecting the presence and sign of an electric charge. It is the simplest type of ionization chamber. See Ionization chamber

The illustration shows a common type of simple gold-leaf electroscope. Gold leaf (L) is used because it is an extremely thin conducting foil which has low mass per unit area and is very flexible. Hence, it responds quickly and vigorously to small electrostatic forces. In the illustration H serves as a grounded electrostatic shield, as well as a shield against air currents. The hard-rubber rod R (illus. a) with its negative charge has set up the charge distribution by the process of electrostatic induction. The response shown is a test for the fact that R has a charge. See Electrostatics

Electroscope

To leave the electroscope with a net charge, a grounded conductor is touched to K so that the surplus electrons on P and L go off to ground, leaving the bound positive charge on K. The ground connection is then broken and R is removed. At this stage (illus. b) the electroscope is said to have a positive charge because there is a positive charge on its leaf system.

If an electroscope has a charge of known sign, as in illus. b, it can be used to test the sign of an unknown charge, as in illus. c, where the metal test ball (T), with its insulating handle (J), has the unknown charge. In the situation pictured, L moves farther away from P as T is brought slowly up toward K, showing that T has a positive charge. If T had a negative charge, L would move toward P, as T slowly approaches K. The converse situation, if the leaf system in illustration c had a negative charge initially, can be readily visualized.

Although electroscopes have been built with a wide variety of geometries, the principle of operation is essentially the same for all. If an electroscope has a scale, permitting quantitative measurements, it is called an electrometer or electrostatic voltmeter. For information on electrometers See Voltmeter

McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.

electroscope

[i′lek·trə‚skōp]

(engineering)

An instrument for detecting an electric charge by means of the mechanical forces exerted between electrically charged bodies.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Electroscope

 

a simple device for the detection of electric charges and the approximate determination of their values. It consists of a metal rod with one or two small light metal leaves attached at the bottom and usually with a small sphere on the other end. The rod is placed in a glass vessel and secured with a plug of insulating material. When the sphere is touched by a charged body, a portion of the charge is transferred from the body to the leaves, and they repel one another (in electroscopes with a single leaf, the leaf is repelled from the rod). From the divergence angle of the leaves it is possible to estimate the value of the charge of the leaves and, consequently, the charge on the body.

REFERENCE

Kalashnikov, S. G. Elektrichestvo, 3rd ed. Moscow, 1970. (Obshchii kurs fiziki, vol. 2.)

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.