Polarization of Light

# Polarization of Light | Physics Class 12 - NEET PDF Download

Polarization

The phenomena of restructuring of electric vectors of light into a single direction is called polarization.

Ordinary light has electric vectors in all possible directions in a plane perpendicular to the direction of propagation of light.

When ordinary light is passed through a tourmaline, calcite or quartz crystal the transmitted light have electric vectors in a particular direction parallel to the axis of crystal. This light is plane polarized light.

[A plane containing the vibrations of polarized light is called plane of vibration.

A plane perpendicular to the plane of vibration is called plane of polarization.]

Polarization can take place only in transverse waves.

Nicol Prism

A nicol prism is an optical device which is used for producing  plane polarized light and analyzing light the same.

The nicol prism consists of two calcite crystal cut at 68° with its principal axis joined by a glue called Canada balsam.

Question for Polarization of Light
Try yourself:
What is the phenomena called when electric vectors of light restructure into a single direction?

Law of Malus

When a beam of completely plane polarized light is incident on an analyzer, the intensity of transmitted light from analyzer is directly proportional to the square of the cosine of the angle between plane of transmission of analyzer and polarizer, i.e.,

I ∝ cos2 θ

When ordinary light is incident on a polarizer the intensity of transmitted light is half of the intensity of incident light.

When a polarizer and analyzer are perpendicular to each other, then intensity of transmitted light from analyzer becomes O.

Brewster’s Law

When unpolarized light is incident at an angle of polarization (ip) on the interface separating air from a medium of refractive index μ, then reflected light becomes fully polarized, provided

μ = tan ip

If angle of polarization is ip and angle of refraction is μ then

ip + r = 90°

Refractive index μ = tan ip = 1 / sin C

where, C = critical angle.

Double Refraction

When unpolarized light is incident on a calcite or quartz crystal it splits up into two refracted rays. one of which follows laws of refraction, are called ordinary ray (O-ray) and others which do not follow laws of refraction, are called extraordinary ray (E-ray). This phenomena is called double refraction.

Dichroism

Few double refracting crystals have a property of absorbing one of the two refracted rays and allowing the other to emerge out. This property of crystal is called dichroism.

Polaroid

It is a polarizing film mounted between two glass plates. It is used to produce polarized light.

A polaroid is used to avoid glare of light in spectacles.

Question for Polarization of Light
Try yourself:
Which law describes the relationship between the intensity of transmitted light and the angle between the plane of transmission of an analyzer and a polarizer?

Uses of Polaroid

(i) Polaroids are used in sun glasses. They protect the eyes from glare.
(ii) The polaroids are used in window panes of a train and especially of an aeroplane. They help to control the light entering through the window.
(iii) The pictures taken by a stereoscopic camera. When seen with the help of polarized spectacles, create three dimensional effect.
(iv) The windshield of an automobile is made of polaroid. Such a mind shield protects the eyes of the driver of the automobile from the dazzling light of the approaching vehicles.

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## Physics Class 12

105 videos|425 docs|114 tests

## FAQs on Polarization of Light - Physics Class 12 - NEET

 1. What is polarization of light?
Ans. Polarization of light is a phenomenon in which the light waves oscillate in a particular plane. This means that the light waves have a specific direction of oscillation, which is perpendicular to the direction of the wave's propagation. The plane of oscillation is known as the polarization plane.
 2. How does polarization occur?
Ans. Polarization of light can occur in several ways. It can be achieved through reflection, where the reflected light is polarized. Polarization can also occur through scattering, where the scattered light is polarized, or through transmission, where only the light waves oscillating in a particular plane are allowed to pass through certain materials, such as polarizing filters.
 3. What are the applications of polarization of light?
Ans. Polarization of light has several applications in various fields. It is used in 3D movie technology, where two different images are projected on a screen, and polarized glasses are used to filter each image to each eye. It is also used in sunglasses, where polarized lenses are used to reduce glare and improve vision. Polarization is also used in the manufacturing of LCD screens, where polarizing filters are used to control the brightness and contrast of the display.
 4. Can all types of light be polarized?
Ans. No, not all types of light can be polarized. Only light waves that oscillate in a particular plane can be polarized. For example, light emitted by a light bulb is unpolarized since the light waves oscillate in different planes. However, light waves emitted by lasers are polarized since the light waves oscillate in a specific plane.
 5. How is polarization of light measured?
Ans. Polarization of light can be measured using a device called a polarimeter. A polarimeter consists of a polarizer and an analyzer, which are placed at different angles to each other. The polarizer is used to polarize the light, and the analyzer is used to measure the amount of polarization. The amount of polarization is measured by the intensity of the light that passes through the analyzer. The greater the amount of polarization, the greater the intensity of the light that passes through the analyzer.

## Physics Class 12

105 videos|425 docs|114 tests

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