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Slit & light interference

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

    Two narrow slits are cut into a sheet of paper and set in front of a laser beam, causing an interference pattern to appear on the wall.
    If the distance from one slit to the third bright fringe is 0.5000004 m
    and the distance from the other slit to the same bright fringe is 0.5000008 m
    calculate the wavelength of the light from the laser.

    2. Relevant equations

    | PmS1 - PmS2 |= m[itex]\lambda[/itex]

    3. The attempt at a solution

    My answer:

    |0.5000004-0.5000008|=(3)[itex]\lambda[/itex]
    0.0000004/3 = [itex]\lambda[/itex]
    [itex]\lambda[/itex] = 0.000000133 m

    edit: my answer uses
    | P3S1 - P3S2|
    whereas the book's answer uses
    | PmS1 - PmS2|

    How would I turn one into the other?

    The book's answer:

    |0.50000030-0.50000165|=3[itex]\lambda[/itex]
    [itex]\lambda[/itex]=0.00000135/3
    [itex]\lambda[/itex]=0.00000045m = 450nm

    I'd like to know where they got the values of:

    PmS1=0.50000030m
    and
    PmS2=0.50000165m
     
    Last edited: Jan 31, 2013
  2. jcsd
  3. Jan 31, 2013 #2

    TSny

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    Did you leave out the "5" after the decimal points? Your work looks correct to me. I don't see where the book's numbers come from either.
     
  4. Jan 31, 2013 #3
    didn's leave anything out :/


    sorry, i edited my original post a second ago.


    edit: my answer uses
    | P3S1 - P3S2|
    whereas the book's answer uses
    | PmS1 - PmS2|

    How would I turn one into the other?
     
  5. Jan 31, 2013 #4

    TSny

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    Is the distance from the first slit to the bright fringe 0.000004 m or 0.500004 m?

    Let m = 3?
     
  6. Jan 31, 2013 #5
    sorry, corrected the mistake.

    the book has been known to make errors in their solutions... but i was wondering if there's something i'm missing
     
  7. Jan 31, 2013 #6

    TSny

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    I think your work is correct.
     
  8. Jan 31, 2013 #7
    alright, thanks
     
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