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Geometrical Optics question

2018 · Q127
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Geometrical Optics question

2018 · Q127

NEETPhysicsGeometrical OpticsMCQ+4 / −1
The refractive index of the material of a prism is 2\sqrt 22​ and the angle of the prism is 30°. One of the two refracting surfaces of the prism is made a mirror inwards, by silver coating. A beam of monochromatic light entering the prism from the other face will retrace its path (after reflection from the silvered surface) if its angle of incidence on the prism is
  1. A
    600
  2. B
    450
  3. C
    300
  4. D
    zero
View written solutionFree

Correct answer: B

For retracing the path, light ray should be normally incident on silvered face.

NEET 2018 Physics - Geometrical Optics Question 26 English Explanation


Applying Snell’s law at point M,

sin⁡isin⁡30∘=21{{\sin i} \over {\sin 30^\circ }} = {{\sqrt 2 } \over 1}sin30∘sini​=12​​

⇒\Rightarrow⇒ sin i = 2×12\sqrt 2 \times {1 \over 2}2​×21​ = 12{1 \over {\sqrt 2 }}2​1​

⇒\Rightarrow⇒ i = 45o

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