A cathode is the negative electrode of a battery or electrolytic capacitor. A cathode is also the reduction electrode in an electrochemical cell. Cathode rays are beams of electrons that emanate from acathode and are most commonly produced by heating a filament in a vacuum tube or by bombarding a target with positive ions.

Metals are excellent conductors of electricity because the outer orbiting electrons (negative charges) in the metal atom are very loosely bound to the nucleus. A traditional and still useful conceptual model, depicts a metal as containing a cloud of electrons with the ability to migrate throughout the metal. Accordingly, any electrical force (voltage) applied to a metal will cause this cloud of electrons to move in response to the force. In contrast, insulators are materials (e.g., rubber and plastic) in which there are few free electrons. Without...