A capacitor is so-called because it has the "capacity" to store electrical energy. It is not an electronic component, but, acting as a tiny rechargeable battery, it provides a temporary power source for an electronic circuit. The more capacitance (measured in farads, F) a capacitor has, the more energy it can store.

How it works

A capacitor stores energy by accumulating electric charges on two metal surfaces placed close together, but partly insulated from each other by a material that is a poor conductor of electricity. This is called a dielectric material. A capacitor is charged by being connected to a battery.

Sometimes, the voltage in an electronic circuit may drop away for a spilt second. This is known as "noise". It may cause devices on the circuit instantly to switch off and restart when the power comes on again. To avoid this happening, a capacitor is connected to the circuit to supply power for that vital split second. This is called filtering. A capacitor used for this purpose is called a “decoupling capacitor” or a “bypass capacitor”.