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JAMB Physics 1986 Question 27

Question 27

Refraction of Light

In Fig. 6, a ray of light in air strikes a glass plate at an angle of incidence of 60°. The reflected ray is observed to be perpendicular to the refracted ray. What is the refractive index of the glass?

Diagram for this question
  1. A.1.73
  2. B.1.50
  3. C.0.87
  4. D.0.57
Show the answer and explanation

Answer: A (1.73)

Explanation

Reflected ray is at 60° to the normal; for it to be at 90° to the refracted ray, the angle of refraction is 180° − 60° − 90° = 30°. n = sin 60°/sin 30° ≈ 1.73.