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Homework Help: Interference and Waves

  1. Nov 9, 2011 #1
    1. The problem statement, all variables and given/known data
    http://img5.imageshack.us/img5/4605/lchuynh177setphys52awee.png [Broken]

    The figure shows the interference pattern that appears on a distant screen when coherent light is incident on a mask with two identical, very narrow slits. Points P and Q are maxima; Point R is a minimum. The wavelength of the light that created the interference pattern is λ = 699 nm, the two slites are separated by rm d = 6 μm, and the distance from the slits to the center of the screen is L = 80 cm . The difference in path length at a point on the screen is ∆s = |s1 − s2|, where s1 and s2 are the distances from each slit to the point.
    1. What is ∆s (in nm) at Point P?
    2. What is ∆s (in nm) at Point Q?
    3. What is ∆s (in nm) at Point R?




    2. Relevant equations
    da=sqr(L^2+(D/2+d/2)^2)
    db=sqr(L^2+(D/2-d/2)^2)

    3. The attempt at a solution
    I know the answer to the first problem is 0.
    But i tried plugging in da=sqr(80^2+(699-3)^2) and im getting it wrong. I tried converting all the units to nm, but then the equation just turns into sqr(80nm^2) because the second term turns into a number close to zero.
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Nov 9, 2011 #2

    PeterO

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    Homework Helper


    No geometry/trigonometry is necessary.

    Think about the requirements for those particular maximum and minimum lines!!!
     
    Last edited by a moderator: May 5, 2017
  4. Nov 9, 2011 #3
    Hmmmm I am almost positive that the pythagorean Theorem must be used. I cant really see it any way. what do you mean by requirements?
     
  5. Nov 9, 2011 #4
    Is the answers 1) 0, 2) 699nm, 3) 1048.85? I believe that the the center is a maxima and Q is the next maxima so that is one full wavelength. R is a minima right after the first maxima so it is 699+349.5 = 1048.85nm. Please get back to me thank you.
     
  6. Nov 9, 2011 #5

    PeterO

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    Homework Helper

    exactly!!!!!!! They ask for path difference, and the maxima and minima occur for specific path differences

    EDIT: I am in East Coast Australia, so time differences will explain any delay in this response.
     
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