Capacitor

A capacitor is a device that is capable of storing charge. It essentially consists of two conducting surfaces separated by an insulating material. The conducting surfaces are called plates of the capacitor and the insulating material is called dielectric. The most commonly used dielectrics are air, mica, paper,etc. A capacitor is generally named after the dielectric used e.g., air capacitor, mica capacitor, paper capacitor, etc. The capacitor may be in the form of parallel plates (parallel plate capacitor), concentric cylinders (cylindrical capacitor) or other arrangement.

Capacitace:

The ability of a capacitor to store charge is known as its capacitance. It has been found experimentally that charge q stored in a capacitor is directly proportional to the p.d. (V) across the plates i.e,

           q 

                   ________                =   constant C

           v              

The constant of proportionality C is called capacitance of the capacitor. The unit of capacitance is 1 C/V which is also called 1 Farad. By definition, capacitance is always a positive quantity. The p.d. across the capacitor increases linearly with increase in charge on capacitor plate. Therefore, the ratio q/V is constant for a given capacitor.