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JAMB Physics 1983 Question 18

Question 18

Dispersion of Light and Colours

Which of the following arrangements in the sequence shown can be used to obtain a pure spectrum of white light?

  1. A.Source, slit, converging lens, prism, converging lens, screen
  2. B.Source, slit, diverging lens, prism, diverging lens, screen
  3. C.Source, converging lens, prism, diverging lens, screen
  4. D.Source, slit, diverging lens, converging lens, screen
  5. E.Source, slit, prism, diverging lens, screen.
Show the answer and explanation

Answer: A (Source, slit, converging lens, prism, converging lens, screen)

Explanation

A narrow slit, a converging lens to make the light parallel, the prism, and a second converging lens to focus each colour sharply on the screen give a pure spectrum.