The separation of light waves with an electric field vector oriented only in a single direction is called polarisation of light. The light polarisation phenomenon occurs due to electromagnetic wave radiation. Sunlight is an example of an electromagnetic wave since it travels through the vacuum to reach the Earth. These waves are called electromagnetic waves because they are produced when an electric field interacts with a magnetic field. There are three types of Polarisation, namely Circular Polarisation, Linear Polarization and Elliptical Polarisation.

The polarization of light is categorised into three categories based on the transverse and longitudinal wave movement. This article will discuss the nature of polarisation, its types, and example. Read on to know more.

What is Polarization?

Polarisation is the property of certain electromagnetic radiations in which the direction and magnitude of the vibrating electric field are related in a specified way. Students can refer to the image below to understand the same.

In the above image, the polarised waves are the light waves in which the vibrations occur in a single plane. The wave direction of vibration is the same for all waves consisting of the plane polarised light. We can see that Plane polarised light vibrates only on one plane. This process of transformation of unpolarised light into polarised light is called Polarisation.

Types of Polarization

There are different types of polarisation, a few of which we have discussed below.

Dielectric Polarization

When a dipole moment is formed in an insulating material because of an externally applied electric field, this behaviour is termed dielectric polarisation. This occurs when the current interacts with the insulating material causing a shift in the charge distribution with positives aligning with an electric field and negative aligning against it. A simple example of this behaviour can be shown using a capacitor. Below you can observe a dielectric material in between two parallel conducting plates.

Ionic Polarisation

This polarisation typically occurs in ionic crystal elements such as NaCl and KCl. This mechanism contributes to relative permittivity. Inside these materials, there is no net polarization in the absence of an electric field. This is because the positive ions cancel out the dipole moments of the negative ions. When an external field is applied, the ions are displaced. This leads to induced polarization. You can see the effect of the external electric field in the figure shown below.

Orientational Polarisation

A permanent dipole moment in the material gives rise to orientational polarisation. This orientational polarisation is seen in materials such as HCl and H2O. These materials have a net permanent dipole moment because of the charge distributions of these molecules. Consider the hydrogen chloride molecule in which the chlorine atom charged negatively, and the hydrogen atoms charged positively. This causes the molecule in hydrogen chloride to be dipolar. In the absence of an electric field, thermal agitation cancels the dipole moment. Else there is no dipole moment even if the material is dipolar. When an electric field is applied, the molecule rotates and aligns with the field, causing a net average dipole moment per molecule. Below is the effect of the electric field shown in a material that exhibits Orientational Polarization.

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Interfacial Polarisation

Interfacial Polarisation occurs when there is an accumulation of charge at an interface between two materials because of an external field. This kind of polarisation is also called space charge polarization. When two electrodes are connected to a dielectric material instead of affecting bound positive and negative charges, i.e. ionic and covalently bonded structures. Interfacial polarization also affects charges. This makes it different from orientational and ionic polarization. interfacial polarization is usually observed in amorphous or polycrystalline solids. The electric field will cause a charge imbalance, mobile charges in the dielectric will migrate over to maintain charge neutrality. This then causes interfacial polarization.

Types of Polarization of Light

There are three types of polarization based on the transverse and longitudinal wave motion, which are as follows:

A) Linear polarisation- When a light wave is polarised linearly, it denotes the electric field that vibrates in a linear direction perpendicular to the wave axis. The magnetic field is vibrating in a perpendicular direction to both the advancement axis and the direction of the electric field. The direction of polarisation is considered the direction of the electric field vibration. The polarization can occur in any other direction perpendicular to the wave axis. Rotation of the polarization by 180° does not lead to a rationally different state.

B) Circular polarisation-Here, the electromagnetic field has a constant magnitude at every point. But the direction rotates at a constant value in a plane perpendicular to the direction in which the way is. A circular polarised wave can rotate in two ways: either in the electric field vector that rotates according to the direction of propagation in a right-hand direction or to the direction of propagation in a left-hand sense. The phenomenon of polarization rises as a result of the fact that light acts as a 2 Dimensional transverse wave.

C) Elliptical polarization- This type of polarization occurs when the tip of the electric field vector creates an ellipse normal to the direction of propagation and traverses any fixed plane. Two linearly polarized waves can be bifurcated from elliptically polarized waves by making them parallel.

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The image given below is the diagrammatic representation of the 3 types of polarisation of light. Students can refer to this article to have a better understanding of the same.

Application of Polarisation

Polarisation is used in many fields. Below provided are a list of applications where Polarisation is used.

• Polarized sunglasses
• Sky polarization and photography
• Display technologies
• Radio transmission and reception
• Plastic industries for performing stress analysis tests.
• 3D movies
• Differentiating between transverse and longitudinal waves.
• Infrared spectroscopy
• Seismology
• In Chemistry, the chirality of organic compounds is tested using polarization techniques. 

FAQs

Here we have provided a few frequently asked questions on the topic types of Polarisation:

Q1. How many types of polarisation are there that depend on the transverse and longitudinal wave motion?
Ans: There are 3 types of polarisation that depend on the transverse and longitudinal wave motion.

Q2. What are the 3 types of polarisation?
Ans: The 3 types of polarisation are Linear polarisation, Circular polarisation and Elliptical polarisation.

Q3. What are the 4 types of polarization?
Ans: The four types are Electronic polarisation, Dipolar/Orientation polarisation, Ionic polarisation and Interfacial polarisation.

Q4. What is linear polarisation?
Ans: Linear polarization or plane polarization of electromagnetic radiation is a confinement of the electric field vector or magnetic field vector to a given plane along the direction of propagation.

Q5. Where is polarisation applied?
Ans: Polarisation is used in many fields such as making sunglasses, plastic industry, seismology, etc.

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