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Homework Help: Distance Between Two Slits

  1. Mar 28, 2009 #1
    1. The problem statement, all variables and given/known data

    Light of 650 nm is incident on two slits. A maximum is seen at an angle of 10.93degrees and a minimum of 11.73degrees. What is the order m of the maximum?

    What is the distance d between the slits?

    2. Relevant equations

    dsin(theta)=m(lambda) - max

    dsin(theta)=(m+1/2)(lambda - min

    3. The attempt at a solution

    So I started out with the two equations, one for the constructive interference and destructive interference. I solved one equation for d, and then substituted that solved equation into the other to try and find m. I don't know if it was an error in math or what, but I can't seem to solve this problem. Is there an easier way that this, or is this the easiest?

    P.S. Sorry I've posted three threads for three different questions, but I'm having trouble with this chapter. Thank you for your patience and your help.
  2. jcsd
  3. Mar 28, 2009 #2


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    Homework Helper

    It sounds good to me. I wrote the two equations
    mL = d*sin(A) and (m+.5)L = d*sin(B) and divided them to eliminate the d.
    This almost resulted in a whole number - one % off. Close enough, I guess.
  4. Mar 28, 2009 #3
    What did you get for your m? I took an m out after I divided the two equations, so it looked like m=(.5sinA)/sinB, which got me about .466330. I tried entering it and it wasn't right. My math is definitely wrong ._.
  5. Mar 28, 2009 #4


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    Dividing the 2 equations, I got
    1 + .5/m = sin(B)/sin(A) = 1.072203
    so .5/m = .072203
    m = 6.92
  6. Mar 28, 2009 #5
    That explains what I did wrong. I figured it out. Thanks for all your help Delphi!
  7. Mar 30, 2009 #6
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