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प्रश्न
Discuss about Nicol prism.
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उत्तर
Principle: Double Refraction
Construction:
- One of the most common forms of the Nicol prism is made by taking a calcite crystal which is a double refracting crystal with its length three times its breadth.
- It is cut into two halves along the diagonal so that their face angles are 72° and 108°.
Nicol Prism - The two halves are joined together by a layer of Canada balsam, a transparent cement.
- A ray of unpolarized light from a monochromatic source such as a sodium vapour lamp is incident on the face AC of the Nicol prism. Double refraction takes place and the ray is split into ordinary and extraordinary rays.
- They travel with different velocities.
- The refractive index of the crystal for the ordinary ray (monochromatic sodium light) is 1.658 and for the extraordinary ray is 1.486. The refractive index of Canada balsam is 1.523.
- Canada balsam does not polarise light.
- The ordinary ray is total internally reflected at the layer of Canada balsam and is prevented from emerging from the other face.
- The extraordinary ray alone is transmitted through the crystal which is plane polarised.
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Uses of Nicol prism:
- It produces plane polarised light and functions as a polariser
- It can also be used to analyse the plane polarised light (i.e) used as an analyser.
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Drawbacks of Nicol prism:
- Its cost is very high due to the scarcity of large and flawless calcite crystals
- Due to an extraordinary ray passing obliquely through it, the emergent ray is always displaced a little to one side.
- The effective field of view is quite limited
- Light emerging out of it is not uniformly plane polarised.
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संबंधित प्रश्न
What is a Polaroid?
Draw a neat labelled diagram showing the plane of vibration and plane of polarisation for polarised light.
If the critical angle of a medium is sin-1(3/5), find the polarising angle.
Using the phenomenon of polarisation, show how the transverse nature of light can be demonstrated.
Show, via a suitable diagram, how unpolarised light can be polarised by reflection.
When a low flying aircraft passes overhead, we sometimes notice a slight shaking of the picture on our TV screen. Suggest a possible explanation.
A ray of light passes from a vacuum to a medium of refractive index (μ). The angle of
incidence is found to be twice the angle of refraction. The angle of incidence is _______.
A) `cos^(-1)(mu/2)`
B) cos−1(μ)
C) `2 cos^(-1) (mu/2)`
D) `2 sin^(-1) (mu/2)`
Unpolarised light is passed through a polaroid P1. When this polarised beam passes through another polaroid P2 and if the pass axis of P2 makes angle θ with the pass axis of P1, then write the expression for the polarised beam passing through P2. Draw a plot showing the variation of intensity when θ varies from 0 to 2π.
State two uses of Polaroid.
What does a polaroid consist of? How does it produce a linearly polarised light?
A ray of light is incident on a transparent medium at a polarizing angle. What is the angle between the reflected ray and the refracted ray?
What is the difference between polarised light and unpolarised light?
Light transmitted by Nicol prism is ______.
Discuss polarisation by selective absorption.
What is a polariser?
What is unpolarised light?
State and obtain Malus’ law.
State Brewster’s law.
Mention the types of optically active crystals with example.
The intensity of transmitted light when a polaroid sheet, placed between two crossed polaroids at 22.5° from the polarization axis of one of the polaroids, is (I0 is the intensity or polarised light after passing through the first polaroid):
