What is capacitor? Explain its principle.

Explanation

Principle of a Capacitor : Capacitance of a charged conductor is appreciably increased by bringing another uncharged or low potential conductor connected to earth near it, provided two conductors remain separated with some non-conducting medium in-between.
Consider a positively charged conducting plate A in air. Bring an uncharged conducting plate Q closer to plate P (Fig. 1) such that negative charge is induced on nearer face of plate Q and equal positive charge on the farther face of plate Q.
The induced negative charge on plate Q tends to decrease the potential of plate P {because -ve charge on Q tries to cancel the effect of +ve charge on P), while the induced positive charge on plate Q tends to increase the potential of plate P. Since induced negative charge of Q is closer to plate P than the induced positive charge, so there will be net decrease in the potential of plate P (Fig. II). In order to make the potential of the plate P same, more charge can be given to it. It is clear that capacity of plate P has increased by bringing an uncharged conducting plate Q closer to it.
If plate Q is now connected to the earth (Figt III) induced positive charge will be neutralized by the electrons coming from earth. Potential of plate P is further decreased as now there is only induced negative charge on plate Q. In order to make the potential of the plate P same, more charge can be given to it. Thus, a large amount of charge can be stored in the above arrangement.

A system of formed (Fig. Ill) is called a parallel plate capacitor. Thus, to store charge, a potential difference. is required between the conducting plates separated by some nonconducting medium.