Permittivity of a medium

Permittivity: Permittivity is analogous to the Conductivity of a conductor, similar to the conductivity which is the property of a material by which it allows free flow of electrons through it, Permittivity is the property of a material by which it allows the free flow of electric field through it.

As we know, If we place two opposite charges at a distance then an electric field is formed in between the space directed from the positive charges to the negative, as shown below:

Now if we place a substance or another medium in between those two plates, First of all the Atoms and the charges in the medium are unpolarized or they are scattered here and there.

Placing of different polarity charge plate

Figure 1: Placing of different polarity charge plate

But because of the force exerted on the charges in the medium by the electric field, the charges and atoms in the medium are polarized or they are all aligned in the same direction, as shown in the figure below:

polarize and unpolarize medium

When the medium ( also called dielectric) is polarized some force is used to align the charges , due to which the medium or dielectric is seen to be opposing the electric field.  But after overcoming the opposing force the electric field continues it’s path.

The property of a material by which despite of this opposing force electric field is allowed to pass though the material is called it’s Permittivity.

Mathematically the Permittivity of a substance is denoted by the Greek letter Epsilon ; \epsilon and the unit of Permittivity is  Farad per Meter F/m.

Permittivity of Vacuum:

The Permittivity of vacuum is of significance in studying Permittivity of substances. Based on Permittivity of vacuum Permittivity of other substances are compared for better understanding and study.

The Permittivity of Vacuum is denoted by \epsilon _0 and is equal to:

\epsilon _0 = 8.854 \times 10 ^ {-12}

 

Relative Permittivity:

Relative Permittivity of a medium or substance is the ratio of it’s Permittivity to the Permittivity of vacuum.

For example if the Permittivity of a substance is \epsilon then it’s relative Permittivity is:

\epsilon_r =\dfrac{\epsilon}{\epsilon_0}