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Capacitor And Capacitance Class 12 Physics Notes

#9. Capacitor And Capacitance 

What is a Capacitor?

The capacitor is the device that is used to store electrical energy. It consisted of two electrical conductors separated by a distance. The space between the conductors may be filled with an insulating material known as dielectric. The ability of capacitor to store charge is known as capacitance.

This is the symbolic representation of the capacitor
symbol of capacitor

Working Of The Capacitor

Before explaining the working of a capacitor, let's consider this basic circuit diagram of parallel plate capacitor. There are two conductors plates separated by a small distance 'd'. The space between the conductors is filled with dielectric. 
capacitor figure

The working of the capacitor can be divided into two parts
(1) charging of the capacitor
(2) discharging of the capacitor

Charging of the capacitor

charging of the capacitor

When we connect the DC supply to the capacitor, one plate is connected to the positive plate and the other plate is connected to the negative plate. When the potential of the battery is applied across the capacitor, the 1st plate becomes positive and the second plate becomes negative. The current tries to flow from the positive plate to the negative plate but, due to the separation of dielectric, it is unable to flow.

An electric field creates across the capacitor. The positive plate collects positive charges and negative plates collect negative charges from the battery. After a particular point, the capacitor holds the maximum amount of charge as per its capacitance with respect to the battery potential, This span of time is called as charging of the capacitor.


When the battery is removed, the charges remain in the two plates for a certain amount of time. Thus the capacitor can store electrostatic energy

Discharging of the capacitor

discharging of the capacitors

If the capacitor connects to the load ( a bulb), the current flows to the load from the positive plate to the negative plate until the charges are disappeared from the both plates. This span of time is called the discharging of the capacitors.

Capacitance

The electric field in the region between two plates depends upon the charges of the plates. And we know that the electric field is directly proportional to the potential (V). Hence we can say,
Q ∝V
Q = C V the proportionality constant C is known as  capacitance
C = Q/V

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