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JAMB Physics 1990 Question 21

Question 21

Refraction of Light

A light wave of frequency 5 × 1014 Hz moves through water which has a refractive index of 4/3. Calculate the wavelength in water if the velocity of light in air is 3 × 108 m s−1.

  1. A.4.5 × 10−7 m
  2. B.6.0 × 10−7 m
  3. C.1.7 × 106 m
  4. D.2.2 × 106 m
Show the answer and explanation

Answer: A (4.5 × 10−7 m)

Explanation

Speed in water = 3 × 108 ÷ (4/3) = 2.25 × 108 m s−1. λ = v/f = 2.25 × 108/5 × 1014 = 4.5 × 10−7 m.