Question

What are polar and non polar dielectrics, give one example of each? Define dielectric constants.

Answer 1

Hint: Polar dielectrics are dielectrics which are made of polar molecules and have zero dipole moment when electric field is zero and non-polar dielectrics are dielectrics which are made of non-polar molecules but have non-zero dipole moment when electric field is zero.

Complete answer:
Dielectrics are materials that are non-conducting but transmit electric effect or electric force, they have no free electrons which travel through the material and thus, they do not carry current like metals.
The diagram below shows polar and non-polar dielectrics when electric field applied is equal to zero ($E=0$ ) and when electric field applied is not equal to zero ($E\ne 0$).

The two types of dielectrics are described as follows,
1. Non-polar dielectrics: In this case of dielectrics the center of the positive and negative charges coincides with each other. They consist of nonpolar molecules, whose dipole moment is zero. When a non-zero electric field is applied all the molecules in the non-polar dielectric align themselves in the direction of the applied electric field. Example of a non-polar dielectric is methane.
2. Polar dielectrics: In this case of dielectrics the center of the positive and negative charges does not coincide with each other, i.e. they have an irregular shape. They consist of polar molecules, whose dipole moment is never zero. When a non-zero electric field is applied all the molecules in the polar dielectric almost align itself in the direction of the applied electric field. Example of a polar dielectric is water.
Dielectric constant: It is a quantity that gives the measure of the ability of a substance to store electrical energy when placed in an electric field. It is also called relative permittivity of a substance and is given by,
$\kappa =\dfrac{\in }{{{\in }_{0}}}$ ….(i)
Where, $\in $ is the permittivity of the substance and ${{\in }_{0}}$is the permittivity of vacuum.
Thus, equation (i) gives the mathematical expression of dielectric constant or relative permittivity of a substance.

Note:
The behavior of polar and non polar dielectrics when placed in an electric field is what is used to differentiate polar dielectrics from non-polar dielectrics and thus should be remembered. Dielectrics are used in many applications such as capacitors and semiconductors.