Question

What is the capacity of a conductor? Explain the principle of a capacitor.

Answer 1

The capacity of a conductor is defined as the ratio between the charge of the conductor to its potential, that is,

$C=\frac{Q}{V}$

Say we have a large plate and we give a positive charge to it. There is a limit to the amount of charge that can be given to the plate because as charge is given its potential rises and beyond a certain limit the charges start leaking. If we get another plate and place it next to this positively charged plate then negative charge will pulled towards the side of this plate which is closer to the positvely charged plate and positive charge on the further side.

This negative charge on plate 2 will reduce the potential on plate 1. At the same time the positive charge on plate 2 will try to increaser the potential of plate 1. However the effect of the closer side of plate 2 holding negative charge will be more. This leads to reduction in the potential of plate 1. So now more charge can be given to plate 1 Now if we earth the outer side of the second plate. Then the positive charge on this side will go to Earth.With this plate 1 will be able to hold even more positive charge. This is the principle of a capacitor.