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The refracting angle of a prism is ‘A’, and refractive index of the material of the prism is cot(A/2). The angle of minimum deviation is:

1. 180° − 2A
2. 90° − A
3. 180° + 2A
4. 180° − 3A

Correct answer: 90° − A

Solution

For a prism, the refractive index μ is related to the angle of minimum deviation (D) and the refracting angle (A) by the formula μ = sin((A + D)/2) / sin(A/2). Substituting μ = cot(A/2), we solve for D and find D = 90° − A.

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