GALAXY

CAPACITOR

Capacitor is an electronic device, which is used to store electric charge or electrical energy a system of two conductors separated by air or any insulating material forms a capacitor as shown below:

WE CANNOT STORE ELECTRIC CHARGE ON A SINGLE CONDUCTOR

The size of a conductor required to store large amount of electric charge becomes very inconvenient because as the charge increases potential of plate also increases. Electric charge generated by a machine can not be stored on a conductor beyond a certain limit as its potential rises to breaking value and the charge starts leaking to atmosphere.

PRINCIPLE OF CAPACITOR

The principle of capacitor is based on the fact that the potential of a conductor is greatly reduced
and its capacity is increased without affecting the electric charge in it by placing another earth connected conductor or an oppositely charged conductor in its neighborhood. This arrangement is therefore able to store electric charge.

Capacitors are designed to have large capacity of storing electric charge without having large dimensions.  

CAPACITANCE OF CAPACITOR

The ability of a capacitor to store electric charge between its plates is its capacity or capacitance.

DEFINITION

The capacitance of a capacitor is defined as:

"The ratio of electric charge stored on any one of the plates of capacitor to potential difference between the plates."

Mathematically

C = Q / V

UNIT OF CAPACITANCE

In S.I. system unit of capacitance is Coulomb / volt OR Farad
Farad is a large unit therefore in general practice we use small units
(1) uF (microfarad) 1 uF = 1x10^-6 F
(2) uuF (Pico farad) 1 uuF = 1x10^{-12 F}