A ray of light is incident on a diamond-air interface at an angle of 40°. The index of refraction of

JAMB Physics 2023 306 views
Source: JAMB · 2023

A ray of light is incident on a diamond-air interface at an angle of 40°. The index of refraction of diamond is 2.42. What happens to the ray of light?

  1. It is refracted into the air
  2. It is reflected into the air
  3. It is absorbed by the diamond
  4. It is totally internally reflected ✓
Explanation

Critical angle: sin c = 1 ÷ n = 1 ÷ 2.42 ≈ 0.413, so c ≈ 24.4°.

The ray meets the interface at 40°, which is bigger than 24.4°. Light is going from the denser to the less dense medium, so it is totally internally reflected.

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