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CBSE Class 12 · 2024 · Wave OpticsMultiple Choice

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Assertion (A): In a Young's double-slit experiment, interference pattern is not observed when two coherent sources are infinitely close to each other.
Reason (R): The fringe width is proportional to the separation between the two sources.
  1. (A)If both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
  2. (B)If both Assertion (A) and Reason (R) are true and Reason (R) is not the correct explanation of Assertion (A).
  3. (C)If Assertion (A) is true but Reason (R) is false.✓ Correct
  4. (D)If both Assertion (A) and Reason (R) are false.

Answer: (C)

Solution

Fringe width , so . As the separation , becomes extremely large and a single fringe spreads over the whole field of view, so no pattern can be resolved — Assertion (A) is true.
Reason (R) states is proportional to the separation ; in fact is inversely proportional to , so R is false.

CBSE Class 12 Board · 2024 · Single correct option

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