Electric Charge

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Related to Electric Charge: electric potential, Electric charge density

charge

charge, property of matter that gives rise to all electrical phenomena (see electricity). The basic unit of charge, usually denoted by e, is that on the proton or the electron; that on the proton is designated as positive (+e) and that on the electron is designated as negative (−e). All other charged elementary particles have charges equal to +e,e, or some whole number times one of these, with the exception of the quark, whose charge could be 1-3e or 2-3e. Every charged particle is surrounded by an electric field of force such that it attracts any charge of opposite sign brought near it and repels any charge of like sign, the magnitude of this force being described by Coulomb's law (see electrostatics). This force is much stronger than the gravitational force between two particles and is responsible for holding protons and electrons together in atoms and for chemical bonding. When equal numbers of protons and electrons are present, the atom is electrically neutral, and more generally, any physical system containing equal numbers of positive and negative charges is neutral. Charge is a conserved quantity; the net electric charge in a closed physical system is constant (see conservation laws). Whenever charges are created, as in the decay of a neutron into a proton, an electron, and an antineutrino, equal amounts of positive and negative charge must be created. Although charge is conserved, it can be transferred from one body to another. Electric current, on which much of modern technology is dependent, is a flow of charge through a conductor (see conduction). Although current is usually treated as a continuous quantity, it actually consists of the transfer of millions of individual charges from atom to atom, typically by the transfer of electrons. A precise description of the behavior of electric charge in crystals and in systems of atomic and molecular dimensions requires the use of the quantum theory.

Electric charge

A basic property of elementary particles of matter. One does not define charge but takes it as a basic experimental quantity and defines other quantities in terms of it.

According to modern atomic theory, the nucleus of an atom has a positive charge because of its protons, and in the normal atom there are enough extranuclear electrons to balance the nuclear charge so that the normal atom as a whole is neutral. Generally, when the word charge is used in electricity, it means the unbalanced charge (excess or deficiency of electrons), so that physically there are enough “nonnormal” atoms to account for the positive charge on a “positively charged body” or enough unneutralized electrons to account for the negative charge on a “negatively charged body."

In line with this usage, the total charge q on a body is the total unbalanced charge possessed by the body. For example, if a sphere has a negative charge of 1 × 10-10 coulomb, it has 6.24 × 108 electrons more than are needed to neutralize its atoms. The coulomb is the unit of charge in the meter-kilogram-second (mks) system of units. See Coulomb's law, Electrical units and standards, Electrostatics

McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Electric Charge

the source of an electromagnetic field that is associated with material carriers; an intrinsic characteristic of elementary particles that determines their electromagnetic interactions. Electric charge is one of the basic concepts in the science of electricity. The entirety of electric phenomena is a manifestation of the existence, motion, and interaction of electric charges.

Two distinct kinds of electric charges are differentiated and are conventionally designated as positive and negative; it has been noted that bodies (or particles) with like charges repel one another and those with unlike charges attract one another, a fact first established by C. F. Dufay in 1733–34. The charge of an electrified glass rod was designated positive, and the charge of a resin rod (specifically, an amber rod) was designated negative. In accordance with this assumption, the electric charge of an electron is negative (the Greek word elektron means “amber”).

Electric charges are discrete: there exists a minimal elementary electric charge, of which the charges of all bodies are multiples. The total electric charge of a closed physical system is equal to the algebraic sum of the charges of its constituent elementary particles (for the common macroscopic bodies these particles are protons and electrons). This total charge is rigorously preserved during all interactions and transformations of the particles in the system. The force of interaction between quiescent charged bodies (or particles) obeys Coulomb’s law. The relationship between electric charges and an electromagnetic field is defined by Maxwell’s equations.

In the International System of Units, electric charges are measured in coulombs.

L. I. PONOMAREV

electric charge

[i¦lek·trik ′chärj]
(electricity)
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
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