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A ray of light is incident at an angle of incidence, i, on one face of prism of angle A (assumed to be small) and emerges normally from the opposite face. If the refractive index of the prism is μ, the angle of incidence i, is nearly equal to:

1. μA
2. μA/2
3. A/μ
4. A/2μ

Correct answer: μA/2

Solution

For a prism with a small angle A, the deviation is minimal, and the ray emerges normally from the opposite face. Using the relation for refraction at the first face, μ = sin(i)/sin(A/2), and for small angles, sin(x) ≈ x (in radians), we get i ≈ μA/2.

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