How Do the Electrons Flow in a Capacitor?

Design

• A capacitor has two metal plates, usually made of thin foil and separated by an electrical insulator called a dielectric. A metal or plastic container surrounds the plates and dielectric. A pair of wire leads protruding from the capacitor's body connect the component to a circuit and carry electric current to the plates.

Charging

• Initially, a capacitor is "empty," having no electric charge. When current flows to the terminals, static electric charges build up rapidly in the plates. The plates hold only a limited amount of charge, however, so as they become saturated, the current slows and stops. At this point, the capacitor is fully charged.

Discharging

• A charged capacitor can release its charge back into the circuit. Current flows from the capacitor plates, draining the static charges. At first, current flows rapidly from the capacitor. As it empties its charge, the outward current flow slows and stops. The capacitor is now empty of charge, but the circuit can immediately recharge it. Charging and discharging the capacitor takes the same amount of time, determined by the capacitor's capacitance -- measured in units called farads -- and the amount of charge current.

Use

• Almost any electronic device that deals with audio, radio or television signals uses capacitors. Computer memory has tiny capacitors to store bits of data. A circuit in a camera pumps charge from its low-voltage battery to produce a high-voltage pulse for its xenon flash lamp. Capacitors in DC power supplies filter noise from electrical power, preventing the noise from interfering with sensitive devices.