A thin prism P₁ with an angle 6° and made of glass of refractive index 1.54 is combined with another prism P₂ made from glass of refractive index 1.72 to produce dispersion without average deviation. The angle of prism P₂ is:
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Question

A thin prism P₁ with an angle 6° and made of glass of refractive index 1.54 is combined with another prism P₂ made from glass of refractive index 1.72 to produce dispersion without average deviation. The angle of prism P₂ is:

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G1 Physics · Accepted Answer

For zero average deviation, (n₁-1)A₁ = (n₂-1)A₂. Thus (1.54-1)×6° = (1.72-1)A₂. Hence A₂ = 6×0.54/0.72 = 4.5°.