Circuit, Electric

circuit, electric: see electric circuit.

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Circuit, Electric 

an aggregate of sources and receivers of electric energy and their interconnecting wires. In addition, an electric circuit may include circuit breakers, switches, fuses, and other protective and switching gear, as well as measuring and monitoring instruments. Occurring within a circuit is the transmission, distribution, and conversion of electric (electromagnetic) or other form of energy linked with the presence in the circuit of an electric current, a potential difference, an electromotive force (emf), and so on. In the sources, some form of energy is converted into electric energy, while in the receivers, electric energy is converted into heat, mechanical energy, or some other form of energy.

The operation of an electric circuit is characterized by the values of the currents and voltages in all its parts, and the relations between these quantities are described by Kirchhoff’s laws (seeKIRCHHOFF’S LAWS). The principal components of an electric circuit are resistors, in which electric energy is converted into heat; inductance coils, which store energy in the magnetic fields of the currents flowing through their windings; and capacitors, which store energy in the electric fields of charges on their plates (seeRESISTOR; INDUCTANCE COIL; and CAPACITOR).

An electric circuit with lumped parameters is a circuit in which each of its components can be referred to a single point of the circuit; the processes in such circuits are described by ordinary differential equations. Circuits with distributed parameters are circuits in which it is necessary to take the geometrical dimensions of its components into account; such circuits are described by partial differential equations.

A linear electric circuit is a circuit consisting of components for which the relations between current and voltage, current and flux-linkage, and charge and voltage are linear. Otherwise a circuit is nonlinear. For linear circuits, Kirchhoff’s laws are written in the form of a system of linear equations, which, when solved, determine the operating conditions of the circuit. For such circuits, the principle of superposition is valid. Nonlinear circuits are computed by graphical or numerical methods using approximations and interpolations for the functions.

A distinction is made between direct-current and alternating-current circuits. The most common among the latter are circuits with harmonic currents. In such circuits, the emf’s and currents are sinusoidal time functions of a single frequency, and their operating conditions are computed by a symbolic method. Three-phase circuits have become very common.

Electric circuits can be represented by a combination of two-terminal networks (sources and receivers of electric energy), four-terminal networks (communication lines, amplifiers, transformers), or multiterminal networks (computer adders and memories).

The concept of electric circuit is used in electrical engineering, radio engineering, automation, bionics, and other branches of science.

REFERENCE

Osnovy teorii tsepei, 4th ed. Moscow, 1975.

P. V. ERMURATSKII