A capacitor is an electrical component used in making electrical circuits. It is made up of two conducting plates separated by a non-conducting material. Capacitors store charge, which can be released at a later time.

You're probably wondering how a circuit would work if a capacitor "breaks" the circuit. Well, when an electron hits one plate, it's electric charge "pushes" an electron on the other plate. This works because electrons repel each other; when one electron comes close to another, they both feel an equal but opposite force away from each other. When current first begins to flow through a capacitor, the capacitor acts as though it has no resistance.

However, as electrons begin to build up on one end of the plate, it slows down incoming electrons for the same reason. Eventually, so many electrons are stuck on one side of the plate that the battery can't push another electron into it. This is one reason for using a capacitor. The current of the circuit starts normally, but then asymptotically approaches zero because of the presence of the capacitor.

The second reason is because of all those built-up electrons. The capacitor now has a stored charge. The amount of charge that can be stored on a capacitor is dependent on its "capacitance" (measured in Farads) and the voltage of the battery it is hooked up to. If either the voltage or the Capacitance increases, the amount of charge that can be held by the capacitor increases. It is worth noting that the capacitor does not store current, but rather voltage. The voltage across the capacitor will be the same as the voltage of the battery used to charge up the capacitor, but the amount of current that leaves the capacitor depends on the resistance of the circuit it is placed in.

The capacitance of a capacitor is measured using a simple equation:

C = Eok (A / D)

Where:

C is the capacitance.

Eo (the 'E' is actually the Greek letter Epsilon) is the permittivity of free space (approximately 8.854x10-12 F/m)

K is the dielectric constant of the material separating the plates (a vacuum is 1)

A is the area of the plates (m2)

D is the distance between the plates (m)

* Current feels no resistance through an uncharged capacitor.
* When fully charged, a capacitor has the same voltage as the battery used to charge it.
* Capacitors alter the current in a circuit asymptotically.

As you can see, the capacitance of a capacitor increases based on the size of the plates and the material separating them, and decreases based on their distance from each other.

Source: http://www.associatedcontent.com/user/503777/nicholas_wuensch.html