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Double slit

  1. Dec 9, 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 d. 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 (lambda_2) of the second laser that would place its second maximum at the same location as the fourth minimum of the first laser?
    Express your answer in terms of d

    2. Relevant equations
    I have (dsin(theta)) = 2(lambda_1)
    and dsin(theta)= (9/2)(lambda_2)

    3. The attempt at a solution

    I set the two equations equal to each other, and solve for lambda_2 and get (2/9)dsin(theta), but then it said the answer does not depend on theta.. so I just guessed and put (2/9)d and it said I was off by a multiplicative factor. basically, I'm confused and do not know how to go about solving this problem. please help!
  2. jcsd
  3. Dec 10, 2007 #2


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    I have (dsin(theta)) = 2(lambda_1)
    and dsin(theta)= (9/2)(lambda_2)
    Check this.
    Second maximum of second laser and fourth minimum of the first laser
  4. Dec 10, 2007 #3
    is it

    (2(lambda_2)L)/d = ((4+.5)(d/8)L)/d
  5. Dec 10, 2007 #4


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