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Homework Help: Depth of pit of CD - why 1/4 of wavelength?

  1. May 7, 2012 #1
    1. The problem statement, all variables and given/known data
    Why does the depth of the pit have to be 1/4 of the wavelength?

    2. Relevant equations
    I understand that this causes two beams to interfere destructively because the path difference resulted is 1/2 of a wavelength - however, I cannot prove this geometrically - can somebody do it?

    3. The attempt at a solution
    there must be a special geometric construction of the two beams that interfere destructively, how does one know that this happens everytime two beams are incident on the CD? Also, I do not understand how the depth of the pit can geometrically imply that the path difference between two beams that are incident on the land and the pit is 1/2 of the wavelength. Please advise, thank you
  2. jcsd
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