In the adjacent diagram,$ CP$ represents a wavefront and $AO$ & $BP$, the corresponding two rays. Find the condition on $\theta$ for constructive interference at $P$ between the ray $BP$ and reflected ray $OP$

187-3

  • [IIT 2003]
  • A

    $cos \theta = 3 \lambda /2d$

  • B

    $cos \theta = \lambda /4d$

  • C

    $sec \theta -cos \theta  =  \lambda /d$

  • D

    $sec \theta -cos \theta  = 4 \lambda /d$

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