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Homework Help: Archived Double slit - find wavelength

  1. Jan 31, 2013 #1
    1. The problem statement, all variables and given/known data

    The following data was obtained via the double slit experiment:

    angle to the eighth maximum = 1.12 degrees
    distance from slits to screen = 302cm = 3.02m
    distance from first to fifth mimum = 2.95cm
    distance between slits = 0.00025m

    find the wavelength.

    2. Relevant equations

    supposed to use this equation to find wavelength:


    3. The attempt at a solution

    problem is, there's no given value for xm or xn

    how can i get this value?

    (oh, and i specifically have to use the equation listed above)
    Last edited: Jan 31, 2013
  2. jcsd
  3. Oct 29, 2016 #2


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    Science Advisor

    ##x_m## is the distance off axis of the mth maximum, numbering the central bright spot as ##m=0##. You can immediately write the distance between the Mth and mth maxima as ##x_M-x_m=(M-m)L\lambda/d##. A little manipulation gets you ##\lambda=d (x_M-x_m)/L (M-m)##. You provided the distance between the M=5 and m=1 maxima. Plugging that and your other data in gets you ##\lambda=610##nm.

    You also gave the angle to the 8th maximum, which tells us that the distance from the axis to the 8th maximum is 3.02 sin(1.12)=0.059m. Plugging that in with M=8, m=0 also yields 610nm.
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