A ray of light is incident on the face AB of a glass prism ABC having the vertex angle A equal to 30∘. The face AC is silvered and a ray of light incident on the face AB retraces its path. If the refractive index of the material of prism is 3, the angle of incidence on the face AB is :
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Updated on : 2022-09-05
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Correct option is A)
Now look at the diagram carefully.
Face AC is silvered means the light ray, falling on it will get reflected.
The ray re-traces its path means, it is moving backward along the same path through which it entered.
This is possible only if the ray is falling on AC perpendicularly.
Look at the triangle △APQ.
In any triangle, the sum of all angles is always 180O
Since ray PQ is perpendicular to AC, ∠AQP=90O
SInce line PR is a normal, ∠APR=90
By angle addition property, ∠APR=∠APQ+∠r
By Snell's law, sinrsini=μ
Answer: The angle of incidence on the face AB is 60O
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