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What is a Capacitor and How much charge can be stored in a capacitor?


A capacitor is an electrical device for storing large amounts of charge and hence electrical energy. A capacitor in the simplest form consists of two parallel plate conductors of any arbitrary shape separated by a small distance with a dielectric medium in between.


The capacitance of a capacitor is numerically equal to the ratio of the amount of charge on either conductor to the potential difference between the conductors forming the capacitor. The capacitance of the capacitor depends on the shape and size of the conductor plates of the capacitor, the dielectric medium placed between the plates, the separation between the plates. The capacitance is independent of the material used in the conductor plates. The SI unit of the capacitance of the capacitor is Farad.

Principle of the capacitor

A metal plate A with the charge +q having an electric potential V such that C= q/V is taken. Here C is the capacitance of the capacitor. An identical metal plate B is brought near the plate A. The positive charge on A will induce a negative charge on B. The induced negative charge on B will reduce the potential of A. As a result the capacitance of A increases considerably. Therefore, more positive charge will be stored in A. If the plate B is earthed. The negative charge on plate B will increase further. The negative charge induced in B will greatly reduce the potential of A. The capacitance of A increases further.

The capacitance of A further increases when the plate B is moved closer to A. The capacitance also increases when a material with a higher dielectric constant is placed between the plates A and B

Charged Stored is the Capacitor

The formula used to determine How much charge is stored in a capacitor? is given below. The charge stored is found using the formula

Q = CV


Q is the amount of charge stored

C is the capacitance of the capacitor

V is the voltage across the plates of the capacitor

Energy stored in a charged capacitor

The amount of work done is stored as electrostatic potential energy U in the capacitor. Thus, energy stored in a capacitor charged to an extent Q is

U = Q2/2C

When the capacitor is fully charged to the extent Q, the potential difference V between the plate is given as

V= Q/C


C is the capacitance

Capacitance of a capacitor

Based on the geometry of the conducting plates the capacitors are of three types. They are

  • Parallel plate capacitor
  • Spherical capacitor
  • Cylindrical capacitor

Uses of the Capacitor

Capacitors find many applications in electronic and electrical circuits. The applications of capacitors include

  • Capacitors are mainly used to store electric charge and electrical energy
  • To generate and detect electromagnetic waves
  • In the radio circuits for tuning the frequency
  • It is used as potential dividers
  • Used to separate the radioactive radiations
  • Capacitors eliminate sparking in the induction coil
  • For tuning of radio circuits
  • The electron beam from CRO is deflected by the capacitor

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