Polarisation of Light

Our aim in this experiment is to observe the polarisation of light using two polaroids.

First, let’s understand the term Polarisation,

Polarisation of light refers to the process of transforming unpolarized light, which consists of light waves vibrating in various planes, into polarised light, where the light waves vibrate in a single plane. Plane polarised light is made up of waves with the same direction of vibration for all of them.

Light is the interaction of electric and magnetic fields travelling through space. A light wave’s electric and magnetic vibrations occur perpendicular to each other. The electric field moves in one direction and is magnetic in another, always perpendicular to each other. Thus, we have one plane occupied by an electric field, with the magnetic field perpendicular to it and the direction of travel perpendicular to both. These electric and magnetic vibrations can occur in numerous planes, leading to unpolarised light. In simple words, polarization refers to the process of transforming unpolarised light into polarised light.

There are several methods for polarisation, including:
- 1. Polarisation by using Polaroids
- 2. Polarisation by Scattering
- 3. Polarisation by Reflection and Refraction

Polaroids are polarising materials made up of molecules oriented in a specific direction.

Natural light is associated with electric field vectors normal to the direction of propagation and lying in all possible planes passing through the light beam. However, all these vectors can be resolved along with two mutually perpendicular directions. Every polaroid has an axis of transmission such that when the polaroid is placed normal to the path of an unpolarised light beam, the component of the electric vector associated with it and parallel to the axis of transmission is allowed to pass through, and the transmitted light is plane polarised. This can be checked by rotating another polaroid placed next to the first polaroid along the beam of light (refer to fig.), a position for which the transmitted intensity vanishes.

This position corresponds to the situation when the axis of transmission of the two polaroids are perpendicular to each other. When these axis are parallel to each other, the transmitted intensity attains a maximum value. Hence, the fractional intensity ranges between 0 and 1 as the two polaroids in the path of the light beam are rotated with respect to each other.

FAQs on Polarisation of Light

What is the meaning of polarisation?

Ans: Polarisation is a property that applies to turning waves that show the geometrical blooming of the oscillations, while the rotating body can be either anticlockwise or clockwise rotation.

Why do light waves exhibit polarisation, but sound waves do not exhibit polarisation?

Ans: Polarisation can only be seen in transverse waves. Sound waves cannot be polarised because they are longitudinal waves.

Does the magnitude of the electric field vector vary in the case of linear polarized light?

Ans: In any form of light, whether it is polarized or unpolarized, the electric field vector’s magnitude fluctuates regularly with time. However, in linear polarized light, the electric field oscillates in one plane perpendicular to the direction of wave propagation.

In a polarised wave, what is the direction in which the electric vectors oscillate?

Ans: When a light wave is polarised, the polaroid absorbs the electric vectors along the propagation direction. As a result, the electric vectors fluctuate in a perpendicular direction to the wave propagation. The pass axis is the name for this direction of polarization wave.