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Double slit problem, finding λ of second laser given data about first laser

  1. Sep 15, 2007 #1
    1. The problem statement, all variables and given/known data

    A laser with wavelength d/8 is shining light on a double slit with slit separation 0.500 rm mm. This results in an interference pattern on a screen a distance L away from the slits. We wish to shine a second laser, with a different wavelength, through the same slits.

    What is the wavelength λ2 of the second laser that would place its second maximum at the same location as the fourth minimum of the first laser, if d = 0.500 mm?

    2. Relevant equations

    http://photo.ringo.com/233/233184793O806463150.jpg [Broken]

    http://photo.ringo.com/233/233184793O806463150.jpg [Broken]

    3. The attempt at a solution

    I have only one attempt left, so I used those equations and made them both sin(θ)= ..., and set them equal to eachother. I got an answer of 1/56 but I do not want to use it and loose my last attempt and get the problem wrong. can anybody confirm this?

    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Sep 15, 2007 #2
    i should also add that i got 1/36, but it said that the first minimum corresponds to m=0 not m=1, would this also apply to the maximum? if so, that is how i got 1/56...
  4. Sep 15, 2007 #3
    Since the maxima and the minima are at the same point, [tex]dsin\theta[/tex] for both cases is the same.

    For the first case, [tex]dsin\theta=2\lambda _1[/tex].

    For the second case, [tex]dsin\theta=\frac{9}{2}\lambda _2[/tex] (m=4)

    Equate the two and solve, your answer seems to be incorrect.
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