Introduction to Capacitors

A capacitor is a device with two terminals that stores electric charge.

Capacitors come in lots of types, shapes and sizes. Some are electrolytic, or polarised, and must be connected the right way around. Their schematic symbol can vary:

Electrolytic:
Non-polarised, ceramic:
Symbols:

A capacitor charges up over time when there is available current and then discharges to release current. It acts as a storage tank for electrical charge.

This is useful for timing (capacitors take time to charge and discharge) and for smoothing (slowly releasing charge when power is cut off)

E.g. in the following circuit:

The LED will shine whilst the power is connected. Once the power is disconnected, the capacitor will continue to power the LED as it discharges, and the LED will fade out.