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.

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