Q87 / 180 · AIIMS 2017 · Physics

Assertion : Two point coherent sources of light $S_1$ and $S_2$ are placed on a line as shown. $P$ and $Q$ are two points on that line. If at point $\mathrm{P}$ maximum intensity is observed then maximum intensity should also be observed at Q. Figure
Reason : In the figure of assertion the distance $\left|S_1 P-S_2 P\right|$ is equal to distance $\left|S_2 Q-S_1 Q\right|$.

  • 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

If maximum intensity is observed at $P$ then for maximum intensity to be also observed at $Q, S_1$ and $S_2$ must have phase difference of $2 m \pi$ (where $m$ is an integer).

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

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