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Homework Help: Find spacing between slits in a double slit experiement

  1. Dec 4, 2016 #1
    1. The problem statement, all variables and given/known data

    2. Relevant equations
    I = Imax cos^2 ((2pi/lambda)dsin(theta))

    .81Imax = Imax cos^2 ((2pi/lambda)dsin(theta))

    To shorten up my work I divided out the Imax

    3. The attempt at a solution

    Not sure where I am going wrong. Is the 2.65 deg not the theta I am suppose to use? I divided out the I max, square rooted both sides, took the inverse cos of the left side to cancel out the cos on the right. Then proceeded to do the algebra.
    111.JPG unnamed.jpg
  2. jcsd
  3. Dec 4, 2016 #2


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    Homework Helper
    Gold Member
    2017 Award

    Check your notes or textbook to see if the factor of 2 (shown in red above) should be there.

    Also, when doing the calculation think about whether or not the angle obtained from the cos-1 should be in radians or degrees.
  4. Dec 5, 2016 #3
    That 2 shouldn't have been in my equation. I found the calculation of inv cos (.9) in radians instead of degrees. That then gave me the correct answer. Thanks for the help!
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