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Determining hole size using laser interference

  1. Dec 11, 2016 #1
    1. The problem statement, all variables and given/known data

    upload_2016-12-11_22-31-15.png

    Lisa makes a hole in aluminum foil. She wants to know the diameter of the hole. She points a laser through the hole. That picture is what appears on the wall that is 1,25 meters behind the aluminum. the distance between every circle is 8mm. the wave length is 633nm.

    http://imgur.com/a/kcaPz
    2. Relevant equations

    dsinx=kλ

    3. The attempt at a solution

    8mm between maximum 1 and 2. so I know that Tanx= 0.0008/1.25
    x= arcTan(0.008/1.25)
    d=kλ/sinx
    d= 1*633*10-9/(sin(arcTan(0.008/1.25))

    I get the wrong answer, why?
     
  2. jcsd
  3. Dec 11, 2016 #2

    BvU

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    What do you get for the sin(arcTan(0.008/1.25) ?
     
  4. Dec 11, 2016 #3
    0.0063998689
     
  5. Dec 11, 2016 #4

    BvU

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    Ok, so degrees and radians isn't the problem and I have to read the problem statement. Is your formula applicable for a single hole (as opposed to two slits) ?
     
  6. Dec 11, 2016 #5
    yes
     
  7. Dec 12, 2016 #6
    Check your value of "k".

    Also, is there a slipped decimal in:
     
  8. Dec 12, 2016 #7
    Two things.

    First, perhaps for learning purposes your class is using that simple equation, but that is not the correct equation for the ring spacing of an Airy disk. Are you sure your class didn't discuss Airy rings and present a slightly different formula?

    Second, the distance to the first Airy minimum is different than the spacing of subsequent minima. You have to go above the first order to answer correctly.
     
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