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Homework Help: Diffraction grating, lines per mm, and how to show the spacing

  1. May 1, 2009 #1
    A diffraction grating is labelled 300 lines mm^-1 (lines per mm)
    Show that the spacing (d) between the lines on the grating is 3.3 x 10^-6m

    i cant really think of any relevant equations. but i'm assuming standard form. i cant believe that the answer would be as simple as converting to m's from mm's

    since there are 300 lines in every mm, i assumed converting to standard for, and metres instead of mm. which might get me close to the answer.

    300 lines per mm = 3000 per cm = 3000000 per m = each line 3 x 10^-6 ?

    this isnt right, clearly. since the anser is 3.3 x 10^-6, i just cant work out how to show it
  2. jcsd
  3. May 1, 2009 #2
    300 lines per mm is equivalent to 3x10^5 lines per m (mulitply by 1000).
    Therefore, the distance between two lines is 1/(3x10^5) = 3.333...x10^6

    Think of it in simple terms: If there are two lines per metre on a grid, then the distance between two lines must be 0.5 m (i.e. 1/2)
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