electric circuit, unbroken path along which an electric current exists or is intended or able to flow. A simple circuit might consist of an electric cell (the power source), two conducting wires (one end of each being attached to each terminal of the cell), and a small lamp (the load) to which the free ends of the wires leading from the cell are attached. When the connections are made properly, current flows, the circuit is said to be "closed," and the lamp will light. The current flows from the cell along one wire to the lamp, through the lamp, and along the other wire back to the cell. When the wires are disconnected, the circuit is said to be "open" or "broken." In practice, circuits are opened by such devices as switches, fuses, and circuit breakers (see fuse, electric fuse, electric, safety device used to protect an electric circuit against an excessive current. A fuse consists essentially of a strip of low-melting alloy enclosed in a suitable housing. It is connected in series with the circuit it is to protect.
..... Click the link for more information. ; circuit breaker circuit breaker, electric device that, like a fuse , interrupts an electric current in a circuit when the current becomes too high. The advantage of a circuit breaker is that it can be reset after it has been tripped; a fuse must be replaced after it has been used
..... Click the link for more information. ; short circuit short circuit, abnormal connection of low resistance between two points of a circuit that usually causes a high, potentially damaging current to flow. To protect against damage, devices such as a fuse or a circuit breaker are used.
..... Click the link for more information. ). Two general circuit classifications are series and parallel. The elements of a series circuit are connected end to end; the same current flows through its parts one after another. The elements of a parallel circuit are connected so that each component has the same voltage across its terminals; the current flow is divided among its parts. When two circuit elements are connected in series, their effective resistance resistance, property of an electric conductor by which it opposes a flow of electricity and dissipates electrical energy away from the circuit, usually as heat.
..... Click the link for more information. (impedance impedance, in electricity, measure in ohms of the degree to which an electric circuit resists the flow of electric current when a voltage is impressed across its terminals.
..... Click the link for more information. if the circuit is being fed alternating current) is equal to the sum of the separate resistances; the current is the same in each component throughout the circuit. When circuit elements are connected in parallel, the total resistance is less than that of the element having the least resistance, and the total current is equal to the sum of the currents in the individual branches. A battery-powered circuit is an example of a direct-current circuit; the voltages and currents are constant in magnitude and do not vary with time. In alternating-current circuits, the voltage and current periodically reverse direction with time. A standard electrical outlet supplies alternating current. Lighting circuits and electrical machinery use alternating current circuits. Many other devices, including computers, stereo systems, and television sets, must first convert the alternating current to direct current. That is done by a special internal circuit usually called a power supply. A digital circuit digital circuit, electronic circuit that can take on only a finite number of states. That is contrasted with analog circuits , whose voltages or other quantities vary in a continuous manner. Binary (two-state) digital circuits are the most common.
..... Click the link for more information. is a special kind of electronic circuit used in computers and many other devices. Magnetic circuits are analogous to electric circuits, where magnetic materials are regarded as conductors of magnetic flux. Magnetic circuits can be part of an electric circuit; a transformer is an example. Equivalent circuits are used in circuit analysis as a modeling tool; a simple circuit made up of a resistor resistor, two-terminal electric circuit component that offers opposition to an electric current. Resistors are normally designed and operated so that, with varying levels of current, variations of their resistance values are negligible (see resistance ).
..... Click the link for more information. , and an inductor inductor, electric device consisting of one or more turns of wire and typically having two terminals. An inductor is usually connected into a circuit in order to raise the inductance to a desired value.
..... Click the link for more information. might be used to electrically represent a loudspeaker. Electrical circuits can also be used in other fields of studies. In the study of heat flow, for example, a resistor is used to represent thermal insulation. Operating electric circuits can be used for general problem solving (as in an analog computer computer, device capable of performing a series of arithmetic or logical operations. A computer is distinguished from a calculating machine, such as an electronic calculator , by being able to store a computer program (so that it can repeat its operations and make
..... Click the link for more information. ).

circuit

or electric circuit

Path that transmits electric current. A circuit includes a battery or a generator that gives energy to the charged particles; devices that use current, such as lamps, motors, or electronic computers; and connecting wires or transmission lines. Circuits can be classified according to the type of current they carry (see alternating current, direct current) or according to whether the current remains whole (series) or divides to flow through several branches simultaneously (parallel). Two basic laws that describe the performance of electric circuits are Ohm's law and Kirchhoff's circuit rules. See also tuned circuit.