Q83 / 180 · AIIMS 2018 (27 May) · Physics

Assertion : Colours are seen in thin layers of oil on the surface of water. Reason : White light is composed of several colours.

  • A
    If both assertion and reason are true and reason is the correct explanation of assertion.
  • Correct answer
    B
    If both assertion and reason are true but reason is not the correct explanation of assertion.
  • C
    If assertion is true but reason is false.
  • D
    If both assertion and reason are false.

Solution

Colours are seen in thin layer of oil on the surface of water, because of interference of light. When white light falls on a thin film of a liquid it will appear bright having colour whose wavelength satisfies the relation $2 \mu t \cos r=(2 n+1) \lambda / 2$. The colour of the film will depend upon the thickness of the film and the angle of refraction.

Hence, the correct answer is option: 'B'.

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