Critical angle for glass-air interface (n_glass = 1.5):
Asin⁻¹(1/1.5) ≈ 41.8°
BAbout 30°
C60°
D90°
Answer & Solution
Correct answer: A. sin⁻¹(1/1.5) ≈ 41.8°
sin θ_c = 1/n = 1/1.5 = 0.667. θ_c ≈ 41.8°. Used in 45-45-90 prisms (binoculars, periscopes): TIR replaces silvered mirrors.
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