NEET 2020 · PhysicsPrevious Year Question
A ray is incident at an angle of incidence i on one surface of a small angle prism (with angle of prism A) and emerges normally from the opposite surface. If the refractive index of the material of the prism is µ, then the angle of incidence i is nearly equal to
Answer: (A) µA. Answer: (A) µA Solution: The ray emerges normally from the second face, so the angle of refraction there is 0°.
- A.µA✓
- B.µA/2
- C.A/(2µ)
- D.2A/µ
Correct Answer
(A) µA
Solution & Explanation
Answer: (A) µA Solution: The ray emerges normally from the second face, so the angle of refraction there is 0°. For a prism, the two internal refraction angles satisfy r₁ + r₂ = A. With r₂ = 0, we get r₁ = A. Apply Snell's law at the first surface: sin i = µ sin r₁ = µ sin A For a small angle prism, sin i ≈ i and sin A ≈ A, so i ≈ µA.
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