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JAMB Physics 1985 Question 33

Question 33

Refraction of Light

Two rays of light from a point below the surface of water are equally inclined to the vertical and are inclined to each other at 60° in water. What is the angle between the rays when they emerge into air? (Take the refractive index of water to be 4/3)

  1. A.41.8°
  2. B.44.1°
  3. C.60.0°
  4. D.83.6°
  5. E.120.0°
Show the answer and explanation

Answer: D (83.6°)

Explanation

Each ray meets the surface at 30°. sin r = (4/3) × sin 30° = 0.667, so r ≈ 41.8°. The emerging rays are 2 × 41.8° = 83.6° apart.