Polarisation of Dielectrics II

The charged particles attract or repel other charged particles because of the electric force.

When we comb the hair with comb due to the friction electric charge $(Q)$ induced in it.

And because of the induction, the charge$(q)$ induced on the paper.

These opposite charges exerts electric force and the paper attracts the comb.

According to the Coulomb's law, Electric Force acting on the charge$(q)$ due to charge $(Q)$ is defined as,

The magnitude of the force in a different medium depends upon the permitivity$(ϵ)$ of the medium.

Electric permittivity is a measure of how well the molecules of substance align under an electric field.

The value for electric permittivity $(ϵ)$ varies according to the nature of the substance.

Therefore the attraction force between the comb and paper can be changed if we change the surrounding medium.

Now we will see the effect on the molecules in the intervening medium because of the change of the electric field.

So, let's study the effect on the molecules because of the change of the electric force.

Dielectric is the non-conducting substance or a bad conductor of electricity.

Dielectric materials can be made to hold an electrostatic charge while dissipating minimal energy in the form of heat.

The few examples of the dielectric materials are,

There is no free electron, therefore, the free movement of charges is not possible.

Therefore, the external electric field induces the dipole movement by re-orienting the molecules of the dielectric.

Because of the induced dipole movement, there is $E_{in}$ in the dielectric.

However, the induced electric field $E_{in}$ does not exactly cancel the external electric field.

The extent of the effect depends on the nature of the dielectric.

In the presence of the electric field, the positive and negative charges are displaced in the opposite direction.

And thus it develops an induced electric dipole$(P)$ in the direction of Electric field.

The dipole moment, (P) per unit volume is called polarisation.

The magnitude of the electric field also changes with the change of the dielectric.

The electric field is the region in which if we place the charged particle then it will experience some electrical force.

The mathematical perfection of the electric field is shown as,

The magnitude of the electric field $(E)$ at point P, which is $R$ distance apart is,

And the direction of the electric field is in the direction of the force that acts on the test charge.

The electric field $(E_0)$ in the vacuum is given as,

The electric field $(E_m)$ in a medium is given as,

Now on dividing the $E_0$ by $E_m$ we get the dielectric constant of the medium.

The dielectric constant is the ratio of the permittivity of a substance to the permittivity of free space.

It measures the ability of a material to store electric charge under the influence of an electric field.

The larger the dielectric constant, the more charge can be stored.

And the energy required to move a charged particle in the electrical field is called electric potential.

The electrical potential varies with the change of the medium.

Mathematically, an electrical potential in a vacuum is defined as,

And the electrical potential in a medium is shown as,

And the dielectric constant is given as,

The electric field inside the conductor is always zero.

Therefore the value of the dielectric constant is infinite for the conductor.

Revision

The electric field is the region in which if we place the charged particle then it will experience some electrical force.

The dielectric constant is the ratio of the permittivity of a substance to the permittivity of free space.

An electrical potential is defined as the amount of energy required to move a charged particle in an electric field.

And the dielectric constant is given as,

The End