The mostly used capacitors are Parallel plate capacitors. There are two very small and thin conducting plates placed parallel to each other at a fine distance lets suppose it as d. Two plates must be separated through a medium. So air, glass, paper etc are used as medium inside these conductors. In these conductors connection of one plate is done with earth and other plate is an insulated plate.
If we provide some charge to the insulated plate. Let’s say that we have provided positive charge to the insulated plate (+Q) and negative charge to the other side of that insulated plate.
The basic symbol that is used for capacitor is
Its symbol is made so due to its internal design. Mainly the fact here to be noted is that, ’don’t think like this that Q is the net charge on the capacitor. We know that the net charge on a capacitor is Zero.’
When the apparatus of parallel plate conductor will set up then due to the charges present on the plates
i.e.
Electric field will be produced. When the distance between the plates will be smaller then the deformity of
near and at the boundaries can be neglected.
When the medium between the plates will be vacuum then the Electric field intensity will be calculated by the formula:
——— equation2
In the above figure
is the surface charge density of each plate.
We know that the electric Intensity between the plates remain same throughout. So:
E=V/d ‘
In the above equation V is the potential difference across the two plates of the capacitor. Therefore
V=Ed= d/
(———–using equation second)
So
=Q/A.
Then V=Qd/A
The capacity of the parallel plate capacitor is given by the formula given below:
i.e.
C= A/ d ——Equation4
An important thing which is to remember is that both the capacitor plates are separated by a medium having some relative permittivity.
So according to this
Now according to the result of above equation we have seen that the capacity of conductor is multiplied by a constant k. So it means when the medium used is air or vacuum then the charge carrying capacity of the conductor becomes k times.
