Electric condensers, also referred to as capacitors, contain a pair of conductors that are separated by an insulator. A conductor is a material designed to hold movable electric charges. When voltage flows across the condenser's conductors, a static electric field results, stores energy and generates a mechanical force between the conductors. The ability of the condenser to hold a charge is measured in farads, or the ratio of the electric charge produced by each conductor to the potential difference (voltage) between them.
Electric condensers are used in tuned circuits, or circuits that form a harmonic oscillator. A harmonic oscillator refers to a system which, when displaced from a position of equilibrium, experiences a restoring force proportional to the amount of displacement. This restoring force creates a constant amplitude and frequency.
Electric condensers work in tuned circuits to select information in frequency bands. Radio receivers, for example, use electric condensers to tune in to a particular radio station.