Polarisation of Dielectrics - Basic

Dielectrics are the insulators.

We can also say that, Dielectrics are the very poor conductor of the electric current.

Because, they do not contain the free charges for conduction.

Dielectrics are basically of two types: () Polar dielectrics, and () Non-polar dielectrics.

Polar dielectrics are dielectrics in which the possibility of center coinciding of the positive as well as negative charge is almost zero.

For example, the molecules of , , etc.

Whereas, in the case of non-polar dielectrics the centers of both positive, as well as negative charges, coincide.

For example, , , etc.

Now, we are interested to know how the dielectrics get polarized.

Let's discuss the polarisation of dielectrics.

First, we discuss the polarisation of nonpolar dielectric substances.

Let's take a nonpolar dielectric substance and put in the electric field.

As the force on the positive charge acts in the direction of the electric field.

And the force on the negative charge acts in the opposite to the direction of the electric field.

Therefore, when the nonpolar dielectric substance is placed in an external electric field .

Then, the centers are displaced with respect to each other as,

Due to which, a net dipole moment will be created within it.

An electric dipole is established, when two electrical charges, of opposite sign and equal magnitude, are separated by a distance.

And the size of the dipole is calculated by its dipole moment.

The dipole moment is the distance between the charges multiplied by the charge.

Now, the right side of the dielectric becomes positive and the left side of the dielectric becomes negative.

And this process is called polarisation.

So, an electric field is induced in the opposite direction to .

Which decreases the total electric field.

Let's discuss the Polarisation of polar dielectrics substance.

As there is already the dipole moment is present in the polar dielectrics.

And when we put it in the external electric field.

Then, the randomly arranged dipoles are just aligned parallel to the electric field as,

And it will be just like in the nonpolar dielectrics.

So, the polarisation can be defined as the electric dipole moments induced per unit volume.

The polarisation is the vector quantity and it is directly proportional to the electric field.

Hence, to make it equal, it will be as,

And the electric susceptibility is the ratio of the polarisation to the electric field.

So, it is the dimensionless quantity.

Revision

When we put the non-polar dielectric substance in the electric field.

It will be just arranged like,

And the similar things happen in the polar dielectric substance.

The polarisation is calculated as,

The End