Let's discuss capacitance of a capacitor
Before we go to the actual discussion, we would like to show you a simple parallel plate capacitor
There is a dielectric material inserted in between these two parallel plates
Now let us connect one battery of voltage V across the capacitor
As soon as we connect the battery across the capacitor, due to electrostatic force
of battery, many free electrons in the plate connected to positive terminal of the battery
will shift away towards the battery. This causes positive charge accumulation at that plate of the capacitor
At the same time, due to attraction of positive plate, free electrons from the battery will
be accumulated in another plate. In other words, it can be said that there is a negative charge accumulation at the plate
which is connected with negative terminal of the battery. As there is a difference in polarity of charge between two plates, there would be a potential
difference or voltage exists between the plates. The charge accumulation increases with time but there is no current crosses the gap between
the plates. This is because these two parallel plates are separated by dielectric, which prevents
flowing of current through it. As much as charge is accumulated on the opposite plates, the voltage across the capacitor increases accordingly
This voltage continues to increase until it becomes exactly equal to the voltage of the
source battery. The process of accumulating charge in the capacitor and associated increase of voltage
across it is called charging of capacitor. This changing process continues depending on the voltage appeared across the capacitor
But it does not depend on the charge accumulated in the capacitor
For same voltage appeared across a capacitor, the charge accumulated in the capacitor may
be different for different capacitor. How much charge is required to be accumulated or stored in a capacitor for developing a
certain voltage across it depends on a typical property of capacitor called capacitance
For a certain capacitor, if voltage appearing across it is V volts for which Q Coulomb charge
is stored in it, then we can write Q is proportional to V or Q equals to C into V
This C is here the constant of proportionality known as capacitance of the capacitor
This equation can be rewritten as C equals to Q by V
Now we will put Q equals 1 Coulomb and V equals 1 volt and we will get C equals 1 Coulomb
by 1 volt. This 1 Coulomb by 1 volt is the unit of capacitance
So 1 unit of capacitance is defined as such capacitance of a capacitor which causes 1
volt potential difference across the capacitor when 1 Coulomb charge is stored in it
This unit of capacitance is named as Farad after name of Michael Faraday
Now it is understood that charge required to be stored in a capacitor for developing
a certain voltage across it is proportional to the capacitance of the capacitor
How much charge is accumulated on the opposite plates of a capacitor for developing a certain
voltage depends on area of the capacitor plates. If area of the plates is larger, more charge can accumulate on the plates for same voltage
across them. If the distance between the plates is smaller, more charge can accumulate on the plates for
same voltage across them. Therefore capacitance is directly proportional to the area of the capacitor plates and it
is inversely proportional to distance between the plates. We can write C is proportional to plate area A and C is proportional to 1 by distance of
the plates small d. That means C is proportional A by d
From here we can write C equals to epsilon into A by d
This epsilon is constant of proportionality here. But it has a significance in determining capacitance of the capacitor
This is permittivity of the dielectric material inserted between the plates of capacitor
If all other factors are fixed, the capacitance depends on the dielectric material used in
the capacitor. Rather to say it depends on the permittivity of the dielectric material used in the capacitor
Hope you got a basic idea of capacitance. Thank you