An equilateral prism has an angle of minimum deviation 30 ° . Find total deviation if a ray is incident normally on the surface.

Question

An equilateral prism has an angle of minimum deviation 30 ° . Find total deviation if a ray is incident normally on the surface., 120 °, 60 °, 90 °, none of these

MARKS App · Accepted Answer

A = 60 ° and δ m = 30 ° μ = sin ⁡ A + δ m 2 sin ⁡ A 2 μ = sin ⁡ 60 + 30 2 sin ⁡ 60 2 μ = sin ⁡ 4 5 ° sin ⁡ 3 0 ° μ = 1 2 1 2 μ = 2 Therefore, θ c r i t i c a l = sin - 1 ⁡ 1 μ θ c r i t i c a l = 45 ° Therefore after 1 s t incidence light goes straight. At second incidence, total internal reflection takes place, and hence deviation is δ = 60 ° .

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