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Question:

A ray of light is incident on a 60° prism at the minimum deviation position. The angle of refraction at the first face (i.e., incident face) of the prism is :

30o

zero

60o

45o

Solution:

Angle of prism, A = r1 + r2
For minimum deviation,
r1 = r2 = r
∴ A = 2r
Given, A = 60o
Hence, r = A/2 = 60o/2 = 30o