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Question

A prism of angle \( 60^\circ \) and refractive index \( 1.5 \) produces a minimum deviation of \(
30^\circ \). What is the angle of incidence?

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Explanation

**Prism minimum deviation** δ_m satisfies n = sin[(A+δ_m)/2]/sin(A/2), A prism angle (degrees), n refractive index, δ_m minimum deviation. For A=60°, n=1.45, sin[(60+δ_m)/2]=1.45×sin30°=0.725, (60+δ_m)/2=46.5°, 60+δ_m=93°, δ_m=33°, illustrating n increase raises δ_m. At minimum deviation: i = (A + D_m/2) . A = 60° , D_m = 30° . i = (60 + 30/2) = (90/2) = 45° . Substituting values gives 45°, which matches expected image position and magnification from mirror/lens formula 1/f = 1/v - 1/u (lens) or 1/f = 1/v + 1/u (mirror), confirming sign conventions and refraction principles.

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