Polarization of Light Waves

Introduction to polarization of light waves:

Light is an electromagnetic wave in which electric and magnetic field vectors vary sinusoidally, perpendicular to each other as well as perpendicular to the direction of propagation of wave of light. In common light sources e.g. sun or a bulb, atoms are the elementary radiators of light. As these atoms act independently, light propagated from such sources in a given direction consists of many independent waves whose plane of vibration are randomly oriented about the direction of propagation. Such light waves are said to be unpolarized or polarized randomly.

In principle, each electric field can be can be resolved into y and z components. We can then fond the net electric field along the y-axis and along the z-axis separately. Thus, unpolarized light can be thought of as the superposition of two polarized waves whose plane of vibration are perpendicu;ar to each other. When unpolarized light is passed through a tourmaline crystal cut with its face parallel to its crystallographic axis AB, only those vibrations of light pass through the crystal, which are parallel to AB. All other vibrations are absorbed. That is why intensity of light emerging from the crystal is reduced. The emergent light from the crystal is called plane polarized light. This phenomenon of restricting the vibrations of light in a particular direction, perpendicular to the direction of wave motion is called polarization of light. The tourmaline crystal acts as a polarizer.


Detection of polarized light:


a) A naked eye cannot distinguish between polarized and unpolarized light. A crystal can be used for making this distinction. A calcite crystal, quartz crystal, nicol prism can be used as polarizer as well as analyser of polarized light.

b)When unpolarized light is seen through a single crystal, intensity of transmitted light decreases, on account of polarization. On rotating the crystal, intensity of polarized light does not change.

c)  However, when light transmitted from Polaroid P1is seen through another polaroid P2 and P2 is rotated, the transmitted fraction of light from P2 falls maximum to zero as the angle between P1 and P2 varies from 00 to 900 respectively. Here, P1 is called polarizer and P2is called analyser.


Identification of given light:


For this we pass the given light through Polaroid, rotate the Polaroid about the incident light and examine the emergent light.

i. If there is no change in the intensity of emergent light, incident light is unpolarized.

ii. If there is a change in the intensity of emergent light with minimum not equal to zero, the incident light is partially polarized.

iii. If the intensity of emergent light changes with minimum equal to zero, the incident light is plane polarized.

Electromagnetic Waves

Waves are the disturbance or oscillations produced in a medium or in space that transfers energy from one place to another. There are different types of waves depending upon the way they propagate and also depending upon the medium requirement for their propagation. Those waves which need medium to traverse are known as mechanical waves while those that do not need any medium are called electromagnetic waves. Also when the direction of propagation of the wave is perpendicular to the direction of disturbance or oscillation, then the waves are called traversal waves while if it is parallel then they are called longitudinal waves.I like to share this Electromagnetic Spectrum Waves with you all through my article.

Definition of Electromagnetic Waves : We Define Electromagnetic Waves as: the waves that are the periodic oscillation of the electric and magnetic field such that the direction of energy transfer is perpendicular to the disturbance.
The electric and magnetic field of the wave are such that they are perpendicular to each other and also they both are perpendicular to the direction of propagation of wave. For example if electric field is in x direction then magnetic field will be either in y direction or z direction so that direction of propagation will be then in z or y direction respectively. This is because EM waves are traverse in nature.

An important feature of EM waves is that they do not need any medium to travel in contrast to mechanical waves. These waves can travel through vacuum. Also they can travel through medium but in that case their speed slows down with the properties of the medium.


Is this topic Wave Theory of Light hard for you? Watch out for my coming posts.

This occurs due to the absorption of energy of EM wave by the atoms of the medium. The speed in a medium depends on the permittivity and permeability of the medium. Speed of Electromagnetic Waves is equal to the speed of light ‘c’ in vacuum which is approximately 3*108 m/s.  in some medium the speed changes as:
v = .
There are different Types of Electromagnetic Waves that exists. Visible light is the only Traveling Electromagnetic Wave that is visible to human eyes. All types of EM waves have different wavelengths and frequency range in which they exist. Representation of all types of EM waves depending on their wavelength and frequency is known as electromagnetic spectrum. Wavelength of electromagnetic spectrum ranges from 10-16 to 108 nm.  The different types of EM waves in EM spectrum are.
Radio waves, micro waves, infrared (IR) waves, visible light, UV or ultraviolet rays, X-rays and gamma rays.