Every circuit is comprised of three major components:

1. a conductive "path," such as wire, or printed etches on a circuit board;
2. a "source" of electrical power, such as a battery or household wall outlet, and,
3. a "load" that needs electrical power to operate, such as a lamp.

There are also two optional components that can be included in an electrical circuit. These are control devices and protective devices. Control and protective devices, however, are not required for a circuit to function. They are optional.

Circuits are made up of two distinct elements:

  • active elements, which are defined as the sources of electrical energy,
  • and passive elements, which carry or use the electrical energy for some specific reason.

Resistors, capacitors and inductors make up the passive elements in circuits. Each is used alone or in conjunction with the others to achieve the desired circuit functions. For example, a circuit that switches on an air conditioner when the temperature is too high would contain the following components:

  • a source of electrical energy, in this case, simple household current;
  • a protective device that senses current flow on the circuit, the circuit breaker in the panel box,
  • a control device that redirects the current, the switch in the thermostat;
  • and a passive element, such as an air conditioner that cools the space down until the circuit opens shutting the air conditioner off.