Explain polarisation by scattering.

The sunlight gets scattered by the molecules present in the atmosphere. Under the influence of the electric field of the incident wave, the electrons in the molecules acquire components of motion in the two mutually perpendicular directions. The accelerating charges are the source of energy radiation. The dots stand for polarisation perpendicular to the plane of the figure and the double arrows show polarisation in the plane of the figure. Consider an observer looking at 90 0 to the direction of the sun. Clearly, charges accelerating parallel to double arrows do not radiate energy towards the observer since their acceleration does not have a transverse component. The radiation scattered by the molecule is therefore represented by dots. It is polarised perpendicular to the plane of the figure as shown in the figure below.

Write definitions of plane of vibration and plane of polarisation. Explain the working process to obtain plane polarised light by Nicol Prism. Draw necessary diagram.

Plane of vibration : The plane in which the vibration of electric field and magnetic field vibrate it is always perpendicular plane with direction of propagation. Plane of polarisation : The plane in which remaining vibration vibrate after the process of polarisation. It is also perpendicular plane to the direction of propagation of light. POLARISATION BY NICOL PRISM :- Principle : When a thin film of Canada balsam is placed between two calcite pieces, the 0-rays of the unpolarised incident light get eliminated through the phenomenon of total internal reflection while E-rays are transmitted unaffected and emerge as a beam of plane polarised light. Working : The principal section ACGE of a Nicol prism. The diagonal AG represents the Canada balsam layer. When ray of unpolarised light passes from a portion of the calcite crystal into the layer of canada balsam, it passes from a denser to a rarer medium. When the angle of incidence is greater than the critical angle ( ≃ 69 ° ), the ray is totally reflected and absorbed by a blackened surface. The E-ray is not effected because it is travelling from rarer medium to denser medium. It gets transmitted through the Nicol prism. Hence a ray passes from Nicol prism get polarised.

How will you distinguish experimentally between ordinary light and plane-polarized light?

Take a polaroid and rotate it. Allow the light to be distinguished to fall on it. If in only one orientation of the pass axis of polaroid, the intensity of light coming out of it is zero then the light is plane-polarized. It shows that the light is confined in only one plane that passes through the pass-axis of polaroid. Hence, the light will be plane polarised. If the incident light is unpolarized, the intensity of light coming out of the polariser will be reduced to half of its original intensity. Rotating the polaroid will have no effect on the intensity of light coming out of it, if it is unpolaized.

State the law of Malus.

According to the law of Malus, the intensity of the polarised light transmitted through the analyser I varies as the square of the cosine of the angle θ between the plane of transmission of the analyser and the plane of the polariser. If I o is the intensity of light coming out of the polariser, this law can be written as: I = I o cos 2 θ

With the help of an experiment, state how will you identify whether a given beam of light is polarised or unpolarised.

In order to identify whether the given beam is polarised or unpolarised, first of all pass it through a polariser and then through analyser. 1. If the intensity of light becomes two times max and two times min then it is a completely polarised light. 2. If the intensity of light changes slightly, then it is a partially polarised light. 3. If the intensity does not changes, then it is a unpolarised light.

Show using a proper diagram how unpolarized light can be linearly polarised by reflection from a transparent glass surface.

When an unpolarized ray of light strikes upon a transparent glass surface, the reflected light gets polarised. But when the reflected and refracted light are perpendicular to each other, the ray of light gets completely plane polarised. Thus, if i p and r be the angle of incidence and refraction, when reflected and refracted light is perpendicular to each other respectively, then: i p + 90 ° + r = 180 ° Using Snell's law: μ = sin ( i p ) sin ( r ) Using the result from above, μ = sin ( i p ) sin ( 90 ° - i p ) μ = sin ( i p ) cos ( i p ) = tan ( i p ) This is the equation for Brewster's law. The angle of incidence i p is called Brewster's angle. Thus, when an unpolarized light is an incident on a transparent glass surface at Brewster angle, the reflected light is plane-polarised light. The diagram for the same is given below:

E M B I B E

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 9 - Polarisation of Light>Exercise>Q 28

EASY

12th ICSE

IMPORTANT

Earn 100

What do you mean by Pass-axis of a polaroid?

Important Questions on Polarisation of Light

MEDIUM

12th ICSE

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 9 - Polarisation of Light>Exercise>Q 29

Mention some applications of Polaroids.

EASY

12th ICSE

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 9 - Polarisation of Light>Exercise>Q 30

A polarizer is used to

EASY

12th ICSE

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 9 - Polarisation of Light>Exercise>Q 31

State the function of a polariser.

EASY

12th ICSE

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 9 - Polarisation of Light>Exercise>Q 32

Unpolarized monochromatic light passes through a single Polaroid filter, oriented horizontally. It then encounters a second filter that is oriented vertically. Which of the following statements is true of the resulting light?

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