# The refracting angle of prism is A and its refractive index is cot(A/2) .Show dat the minimum deviation produced by the prism is (180°_2A)

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by iqbal9692

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by iqbal9692

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When the light rays are incident so that minimum deviation occurs,

angle of minimum D = 2 i - A and A = 2 r => r = A/2

Mu = cos A/2 / sin A/2 = sin (90 - A/2) / sin r

Hence it means that i = 90 - A/2

D = 2(90 - A/2 ) - A = 180 - 2 A

angle of minimum D = 2 i - A and A = 2 r => r = A/2

Mu = cos A/2 / sin A/2 = sin (90 - A/2) / sin r

Hence it means that i = 90 - A/2

D = 2(90 - A/2 ) - A = 180 - 2 A