Polarization of Light

What is Polarization?

Polarization, in Physics, is defined as a phenomenon caused due to the wave nature of electromagnetic radiation. Sunlight travels through the vacuum to reach the Earth, which is an example of an electromagnetic wave. These waves are called electromagnetic waves because they form when an electric field interacts with a magnetic field. You will learn more about that later in the article, but now for some recap. In the chapter on waves, you learned about two types of waves, transverse waves, and longitudinal waves.

Transverse waves

Transverse waves are waves, i.e. movement of the particles in the wave is perpendicular to the direction of motion of the wave. For example, the ripples when you throw a stone in water. Longitudinal waves are when the particles of the medium travel in the direction of motion of the waves. For example, the motion of sound waves through the air.

Light is the interaction of electric and magnetic fields travelling through space. The electric and magnetic vibrations of a light wave occur perpendicularly to each other. The electric field moves in one direction and magnetic in another though always perpendicularly. So, we have one plane occupied by an electric field, the magnetic field perpendicular to it and the direction of travel which is perpendicular to both. These electric and magnetic vibrations can occur in numerous planes. A light wave that is vibrating in more than one plane is known as unpolarized light. The light emitted by the sun, by a lamp or a tube light are all unpolarised light sources. As you can see in the image below, the direction of propagation is constant, but the planes on which the amplitude occurs is changing.

The image here shows its various types:

Polarization of Light

The other kind of wave is a polarized wave. The polarization of light or any other wave refers to the removal of all but one plane so that the vibrations of the wave occur on only one plane. In the image above, you can see that a linearly polarized wave vibrates on only one plane. The process of transforming unpolarised light into the polarized light is known as polarization. The devices like the purple blocks you see are used for the polarization of light.

Types of Polarization

Following are the three types of polarization depending on the transverse and longitudinal wave motion:

  • Linear polarization
  • Circular polarization
  • Elliptical polarization

Linear Polarization

In linear polarization, the electric field of light is limited to a single plane along the direction of propagation.

Circular Polarization

There are two linear components in the electric field of light that are perpendicular to each other such that their amplitudes are equal, but the phase difference is \(\frac{\pi }{2}\). The propagation of occurring electric field will be in a circular motion.

Elliptical Polarization

The electric field of light follows an elliptical propagation. The amplitude and phase difference between the two linear components are not equal.

Methods used in the polarization of light

There are few methods used in the polarization of light:

  • Polarization by Transmission
  • Polarization by Reflection
  • Polarization by Scattering
  • Polarization by Refraction

Polarization Applications

Following are the applications of polarization:

  • Polarization is used in sunglasses to reduce the glare.
  • Polaroid filters are used in plastic industries for performing stress analysis test.
  • Three-dimensional movies are produced and shown with the help of polarization.
  • Polarization is used for differentiating between transverse and longitudinal waves.
  • Infrared spectroscopy uses polarization.
  • In Chemistry, the chirality of organic compounds are tested using polarization technique. 

Stay tuned with BYJU’S to learn more about the polarization of light using the methods listed above.

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