Polarization of Light: Types, Methods & Applications

Polarization of light is an event caused by the vibration of light waves limited to a distinct plane. Polarization can be defined as a “phenomenon which is caused due to the wave nature of electromagnetic radiation.” 

Waves like these are often called electromagnetic waves due to the fact that they form only when electric fields interact with magnetic fields. Light waves travelling only in a single plane are called polarized light waves. In polarization, which is a property of electromagnetic radiation, the magnitude and direction of the vibrating electric field are related in a particular manner. Two types of waves are usually involved in this phenomenon, they are:

• Transverse waves
• Longitudinal waves

Polarization is a property of light that can be seen in transverse waves. One of the primary examples of Electromagnetic Waves is when Sunlight travels through the vacuum to reach the Earth.

Key Terms: Polarisation of Light, Electric Field, Electromagnetic Waves, Transverse Waves, Longitudinal Waves, Wave Nature, Light

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Polarization of Light

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Polarization is known as the process that transforms unpolarized light into a polarized one. The waves that are formed when an interaction takes place between the magnetic field and electric field are known as electromagnetic waves.

Polarization of Light

Polarization of Light can be defined as:

There are two types of waves that exist:

• Transverse Waves: The waves in which the movement of the particles is perpendicular to the waves’ direction of motion are known as transverse waves. One example of Transverse Waves is the rippling of water.
• Longitudinal Waves: When particles of the medium travel in the direction of the motion of the waves, these waves are known as longitudinal waves.

• Light is produced as the result of the interaction of magnetic and electric fields which travel through space.
• There exists a plane of the electric field, one of the magnetic fields which are perpendicular to it and there is a direction of travel of light which is perpendicular to both these planes.
• The vibrations of light waves in these two fields are perpendicular to each other.
• Unpolarized light is a light wave which vibrates in more than one plane. Some of the sources of unpolarized light are: Sunlight, Light by a tube, Light by a lamp, etc.
• The other kind of wave is a Polarized Wave, wherein the vibrations occur in a single plane.
• In plane-polarized light, for all waves, the direction of vibration is the same.
• The direction of propagation of light is constant but what changes is the planes in which the amplitudes occur.

How do Transverse Waves show Polarization?

A transverse wave, as per the above image, vibrates up and down perpendicular to the wave propagation direction. 

• Since there are three dimensions, two directions perpendicular to the propagation direction can be observed.
• Hence, if the wave is propagating in the Z direction, then the wave can be seen to oscillate in the X or Y direction, or a combination of them in overlay directions.
• Thus, the shear wave consists of two polarizations, each for either direction of propagation. 
• If you have a polarized light-sensitive medium (examples including eyeglasses), you can simply detect the polarized light.
• For instance, assume two polarisations.
• One aligned to the X-axis, followed by rotating the other.
• It can be seen that the light intensity is cos2θ (here, θ = relative angle between the preferential directions of the modulator).

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Types of Polarization

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Depending on the motion of transverse and longitudinal waves, there are three types of polarization:

• Linear polarization
• Circular polarization
• Elliptical polarization

Linear Polarization

The type of polarisation in which the electric field of light is limited to one single plane that is along the direction of propagation is known as Linear Polarization.

Elliptical Polarization

Both the phase difference and amplitude between the two linear components are not equal in Elliptical Polarisation.

Circular Polarization

The electric field of light follows a Circular Propagation. The two linear components that exist in the electric field are such that they have the same amplitudes but different phase differences.

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Methods used in Polarization of Light

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Polarization, according to physics, can be expressed as a phenomenon induced by the wave nature of electromagnetic radiation. 

Unpolarized, Plane-polarized Vertically, Plane-polarized Horizontally

The polarization of light uses a few methods which are:

Polarization by Refraction

Most of the light in the refracted ray is unpolarised, having just one or two polarised components. The refracted ray is only polarised partially.

Polarization by Transmission

In this method, the transmission is capable of blocking one plane out of two planes of vibration of the electromagnetic wave.

Polarization by Reflection

In the reflected ray, most of the light is polarised and is parallel to the plane. It has a few unpolarised ones. Thus the reflected ray is also partially polarized.

Polarization by Scattering

On a molecule or on an atom, when light falls, it absorbs the energy of light and then re-emits it in various different directions. This can be described as the Polarization by Scattering.

Polarization by Reflection and Refraction

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Polarization Applications

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The following are the applications of polarization:

• Sunglasses use Polarization to reduce glare.
• Plastic Industries use polaroid filters for performing stress analysis tests.
• Polarisation is one of the major reasons behind the production and screen shows of three-dimensional movies. 
• Polarization helps differentiate between transverse and longitudinal waves.
• Polarization is also used by Infrared spectroscopy. 
• To study earthquakes and seismology, polarization is used. 
• In Chemistry, polarization techniques are used for testing the chirality of organic compounds.
• Polarization helps identify thermally tempered lenses.
• Applications of Polarization are used in ophthalmic instruments, aiding the elimination of strong reflection from a patient's cornea
• Polarization of light can be seen when light passes through the atmosphere.

Brewster’s law

Brewster’s law states that, at a specific angle of incidence, the reflected ray is fully polarised. The angle between the reflected and refracted ray is 90°. Thus, the Total angle = 90°, if considering that, i = i_B, This is when the angle of incidence is equivalent to Brewster’s angle.

As per Snell’s law,

Now, when light is incident at Brewster’s angle, then

i_B + r  =  90°

⇒ r = 90° − i_B

⇒ Thus, sin r = sin (90° − i_B) = cos i_B

After replacing the value of sin r in the formula of μ.

μ = sin i_B ⁄ cos i_B

Hence, μ = tan i_B

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Things to Remember

• Polarisation is a property of light that can be seen in transverse waves. Light waves travelling only in a single plane are called polarized light waves.
• The waves that are formed when an interaction takes place between the magnetic field and electric field are known as electromagnetic waves.
• There are two types of waves, namely: transverse waves and longitudinal waves.
• Depending on the motion of transverse and longitudinal waves, there are three types of polarisation: Linear, Elliptical and Circular.
• Polarisation is one of the major reasons behind the production and screen shows of three-dimensional movies. 
• Polarization helps differentiate between transverse and longitudinal waves.

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Previous Year Questions  

1. When hydrogen atom is in its first excited level, its radius, is….
2. When an electron does transition from n=4 to n=2 , then emitted line spectrum will be….​..
3. α -particle consists of….
4. An electron of a stationary hydrogen atom passes from the fifth energy level….
5. Complete the equation for the following fission process…. [NEET 1998]
6. Using non-relativistic approach, the speed of electron in this orbit will be…. [NEET 2015]
7. When the glancing angle of incidence of light on a material is...[COMEDK UGET 2004]
8. Two waves having intensity ratio 25 : 4 produce interference. The ratio of maximum to minima intensity is...[COMEDK UGET 2004]
9. In Young's double slit experiment,1^st dark fringe occurs directly...[COMEDK UGET 2009]
10. In the diffraction pattern due to a single slit linear width of the central max...[COMEDK UGET 2007]
11. In Newton ring experiment, monochromatic light is replaced by white light...[COMEDK UGET 2008]
12. In diffraction through a single slit experiment, slit width is halved...[COMEDK UGET 2004]
13. Which of the following is false for interference of light?...[JKCET 2012]
14. Which of the following is true for the minimum angular separation of two stars...[JKCET 2012]
15. Values for Brewster's angle can be...[JKCET 2015]
16. Unpolarized light falls on two polarizing sheets placed one on top of other….[JKCET 2013]
17. In Young's double slit experiment using monochromatic light of wavelength   \(\lambda\) ….[AMUEEE 2018]
18. In a single-slit diffraction experiment, the width of the slit is reduced by...[JKCET 2012]
19. the wavelength of light illuminating the slits is….[JKCET 2013]
20. Colours in thin films are due to….[JKCET 2008]

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