In a Young's double-slit experiment, the path difference between two interfering light waves at a point on the screen is . What is the ratio of the intensity at this point to the maximum intensity at the central bright fringe?

Answer and explanation

Correct answer: B.

  1. Step 1: Relate path difference to phase difference: .
  2. Step 2: The intensity formula for interference of two identical coherent sources is .
  3. Step 3: Calculate: . Therefore, .
Answer
.
Why not the others: uses ; corresponds to (path difference ); forgets to square the cosine.

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