Capacitors And Dielectrics

Electrical Capacitance

A capacitor is a device that stores electrical potential energy and electric charge. Electrical capacitance is related to its ability to store the electric charge.
​If some charge is given to a conductor, then it is raised to some potential. The potential of the conductor increases as we increase the amount of charges.

Let charge $q$ is given to a conductor so that its potential rises through $V$. Then, \[q ∝V\] \[q = CV\] The proportionality constant $C$ is called the capacitance of the conductor. It does not depend upon the material of the conductor.

It depends upon;
1. Shape and size of the conductor.
2. Relative permitivity or dielectric constant of the medium in which the conductor lies.

Capacitance of a conductor is defined as the ratio of the charge on it to its potential due to that charge. \[\text{If V=1, then,}\] \[C=q\]

[Also See: Electric Potential at a Point]

Thus, capacitance of a conductor may also be defined as the charge required to raise its potential through $1$ unit.

The SI unit of capacitance is $\text{Farad (F)}$ and its CGS unit is $\text{e.s.u.}$

\[1\text{ Farad (F)}=\frac{1 \text{ Coulomb}}{1 \text{ Volt}}\]
Thus, if one coulomb of charge raises the potential of a conductor through one volt, then, the conductor is said to have one Farad of capacitance.

[Also See: Coulomb’s Law]