Capacitor And Capacitance

Capacitor :

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 arrangements

Capacitance :

Parallel plate capacitor connected to battery

The ability of a capacitor to share Charge is known as it's capacitance

Consider a parallel plate air capacitor connected to a battery. The  electrons from plate 'A' attracted by the battery and these electrons start pilling upon plate 'B' . This action is reffered as the charging of the capacitor because capacitor plates are being charged. 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∝ V

q/V =Constant = C

The constant of proportionality C is called capacitance of capacitor . The unit of capacitance is farad

1 C/V = 1 farad

• By definition capacitance is always a positive quantity
• The p.d across the capacitor increases linearly with increase of Charge on the capacitor plate there fore the ratio q/V is constant for a given capacitor

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