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Homework Help: Question about Interference

  1. Apr 20, 2007 #1
    1. The problem statement, all variables and given/known data

    Consider two light rays propagating from point A to point B in the figure, which are 3(lambda)/4 apart. One ray follows a straight path, and the other travels at a 60 degree angle to that path and then reflects off a plane surface to point B. Both rays have wavelength lambda. View Figure


    Find the phase difference between these two rays at point B. Answer in terms of pi.

    2. Relevant equations

    No equations were provided. But according to my handy textbook:

    Phase Difference = 2(pi)(change in x)/(lambda) + change in initial phase

    3. The attempt at a solution

    (Phase Difference) = 2(pi)[3lambda/4lambda] + (60 degrees * 2pi/360 degrees)
    = 1.83pi

    any ideas?
  2. jcsd
  3. Apr 20, 2007 #2
    first of all u havent understood really what phase difference is....
    it has nothing to od with angle between the rays...
    study some more about phase difference articls on net or yourhandy textbook
    so 60 is not initial phase diff
    as initial is not given we can take it as zero is uppose
    change in x is difference in path travelled by the two rays....
    here 1 ray travels 3lambda /4
    now find the path travelled by the other ray by considering the triangle and laws of reflection
    i =r

    you will find the triangle to be equilateral
    so change in x = 2X 3lambda/4 - 3lambda/4=3lambda/4
    now put in your eqn
    you will find the ans
    i hope no problems...but you got some conceptual probs go figure them out:biggrin:
  4. Apr 20, 2007 #3
    Thanks for the help. I'll definitely have to look over the inherent phase difference information in my book.
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