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Question : 15
Total: 26
(a) Show using a proper diagram how unpolarised light can be linearly polarised by reflection from a transparent glass surface.
(b) The figure shows a ray of light falling normally on the faceA B
AC
(b) The figure shows a ray of light falling normally on the face
Solution:
(a) Diagram
Polarisation by reflection
(b) Justification
Writing yes/no
(a) The diagram, showing polarisation by reflection is as shown.
[Here the reflected and refracted rays are at right angle to each other.]
∴ r = (
− i B )
∴ µ = (
= tan i B )
Thus light gets totally polarised by reflection when it is incident at an anglei B i B = tan − 1 µ
(b) The angle of incidence, of the ray, on striking the faceAC i = 60 ∘
Also, relative refractive index of glass, with respect to the surrounding water, is
∴ µ r =
=
Alsos i n i = s i n 60 ∘ =
=
= 0.866
For total internal reflection, the required critical angle, in this case, is given by
s i n i c =
=
≃ 0 − 89
∴ i < i c
Hence the ray would not suffer total internal reflection on striking the faceAC
Polarisation by reflection
(b) Justification
Writing yes/no
(a) The diagram, showing polarisation by reflection is as shown.
[Here the reflected and refracted rays are at right angle to each other.]
Thus light gets totally polarised by reflection when it is incident at an angle
(b) The angle of incidence, of the ray, on striking the face
Also, relative refractive index of glass, with respect to the surrounding water, is
Also
For total internal reflection, the required critical angle, in this case, is given by
Hence the ray would not suffer total internal reflection on striking the face
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