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A prism of refractive index μ and angle of prism A is placed in the position of minimum angle of deviation. If minimum angle of deviation is also A, then in terms of refractive index, value of A is

Asked in JEE Main 25th July 2nd Shift 2021 · Deviation and minimum deviation

• (1) 2 cos⁻¹(μ/2)
• (2) sin⁻¹(μ/2)
• (3) cos⁻¹(μ/2)
• (4) sin⁻¹(√(μ-1)/2)

Step-by-step solution

Why the other options are wrong

• (2) Uses sine instead of cosine and also drops the factor 2 on the half-angle.
• (3) Gets A/2, not A: forgets to double.
• (4) Uses a half-angle identity wrongly instead of sin A = 2 sin(A/2)cos(A/2).

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