Critical angle for diamond (n = 2.42):
A45°
B60°
C90°
DAbout 24.4°
Answer & Solution
Correct answer: D. About 24.4°
sin θ_c = 1/n = 1/2.42 ≈ 0.413. θ_c ≈ 24.4°. Small θ_c means light easily gets trapped inside — multiple TIRs cause diamond's brilliance (light enters but takes many internal reflections before exiting toward viewer).
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