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Diffraction Gratings, confusing question.

  1. Jan 26, 2013 #1
    1. The problem statement, all variables and given/known data

    f3e51k.jpg

    zmgpkg.jpg

    2. Relevant equations

    λ=xd/nl
    3. The attempt at a solution

    Im having some difficulty with the variables, is d= lines/m? and n= 27? from the 50 mark to the yellow mark. then x would be 27*(4.35*10^-6) and l would be 100cm=1m ?
     
  2. jcsd
  3. Jan 27, 2013 #2

    mfb

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    d is the distance between lines at the grating.
    n is the order of the line. As you have just one line for each color (0 would correspond to light directed towards the tube), it is 1.

    That looks like xd, but it has no units and where does the value of 27 come from?

    Right
     
  4. Jan 27, 2013 #3
    27 lines from thr 50 to yellow
     
  5. Jan 27, 2013 #4

    mfb

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    Those are lines on the ruler, they are completely arbitrary (you could use a ruler with mm-marks as well). 13.5cm is the physical quantity, it does not depend on the type of ruler.
     
  6. Jan 27, 2013 #5
    i just assumed that because of the each etched mark is 4.35*10^-6 apart, so d would be 4.35*10^-6 but x would be that times the 27 lines from the distance from central to the node.

    So x =.135m d= 4.35*10^-6 l =1 and n= 1 so really the calculation is (.135*4.35*10^-6) ?
     
  7. Jan 28, 2013 #6

    mfb

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    With units, yes.

    Those lines ~4µm apart are at the diffraction grating, not at the ruler.
     
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