A ray of light enters a glass prism of refractive index normally on one face. What is the maximum refracting angle of the prism such that the ray does NOT suffer total internal reflection at the second face and emerges into air?
Answer and explanation
Correct answer: A.
- Step 1: For normal incidence on the first face, the angle of incidence is , which gives .
- Step 2: The relation between prism angle and internal angles is .
- Step 3: For the ray to emerge at the second face, the angle of incidence must be less than or equal to the critical angle: . Thus .
Answer
.
Why not the others: is the critical angle for water; causes total internal reflection inside the glass; is unphysical.
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