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Assertion: An excessively thin film appears dark in reflected light. Reason: The film absorbs selected radiations falling on it.

Options

  1. AAssertion is True, Reason is True; Reason is a correct explanation for Assertion
  2. BAssertion is True, Reason is True; Reason is not a correct explanation for Assertion
  3. CAssertion is True, Reason is False
  4. DAssertion is False but, Reason is True.

Correct answer

C. Assertion is True, Reason is False

Step-by-step solution

This phenomenon occurs because of the interference of the two light waves. One from the top surface of the film that got reflected and the other from the second surface. The light from the second surface goes total internal reflection. The two light waves have path difference of λ 2 when t < < λ which is destructive interference and hence the film appears dark. Hence, Assertion is True, Reason is False.

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