An electric circuit is a path along which current can flow. This is a rather broad definition because under the right conditions almost any object can conduct electricity. For example, air is usually considered an insulator (that is, a substance that blocks the flow of electricity), but at sufficiently high voltages air experiences dielectric breakdown: the electrons are stripped from its atoms and become mobile charge-carriers. Under these conditions, air readily conducts an electric current, as when lightning strikes.

In the context of man-made devices, an electric circuit is usually a pathway designed to permit the controlled flow of electricity. Simple circuits consist of three of components: (1) a source of electrical power, usually called a voltage source; (2) a load, that is, something which consumes electrical power, either by storing it up temporarily or dissipating it as heat; and (3) conductors, which allow the free passage of electricity...