A capacitor, (also known as a condenser in some parts of the world)  is a passive electronic component used to store energy.  It consists of a pair of conductors separated by an insulating material called a dielectric. When a potential difference exists across the conductors (voltage being applied), an electric field is present in this dielectric. This field stores energy and actually produces a mechanical force between the conductors.

The amount of energy stored, or capacitance, is measured in farads.  This is named after the English physicist, Micheal Faraday, who discovered the capacitive phenomenon.  In common application, the actual number is quite often so small that micro-farads (or mfd, μf) is used.  For example, on a typical fan moter may require a 5μf capacitor to operate.

Capacitors are used in a wide range of applications, including: energy storage, pulse generation and application, power conditioning and filtration, power factor correction, signal processing, motor starting and running.  They are used in strobe lights, computer circuits, air conditioners, electric motors and microwave ovens among many, many other applications.

They can be dangerous, though, because they do store energy and when fully charged can deliver a high voltage shock.  A capacitor in an air conditioner can discharge 370Volts AC (VAC).  That kind of charge can seriously hurt anyone who isn’t careful.