The capacity of a capacitor is measured in farads. A capacitor has a capacity of 1 farad when a charge of 1 coulomb increases the potential, between its plates, by 1 volt.

The capacity depends on four things: a) the higher the voltage used to charge the capacitor the more energy it will store; b) the larger the sizes of plates and the greater their number the more energy will be stored; c) the closer are the positive and negative plates the greater is the charge; d) some insulators store greater charge than others.

Capacitor in A-C Line

When a capacitor is connected into a circuit through which alternat ing current is flowing, the plates of the capacitor are charged negatively or positively.

In order to show the action of a capacitor, in an a-c line, connect a capacitor in series with a lamp and plug into the a-c lighting. The lamp will glow provided its resistance does not prevent. Then connect another capacitor in parallel and the lamp will glow brighter. 

Connecting more capacitors and increasing the capacity we increase the glow. Thus, capacitors oppose the flow of current.