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Diffraction gratings and intensity

  1. Apr 13, 2009 #1
    1. The problem statement, all variables and given/known data

    The interference pattern in this image:
    http://session.masteringphysics.com/problemAsset/1074248/3/22.P45.jpg
    is seen on a screen 1.0m behind an 950 lines/mm diffraction grating.

    What is the wavelength of the light? (expressed in nanometers to 2 sig figs)

    2. Relevant equations

    I know that the equation relating the variables is: d sin(theta)=m(lambda) where theta is the angle from the center maximum to the mth maxima. d being the distance between slits in the grating.

    And using the small angle approximation I think you can replace sin(theta) with y/L where y is the distance between the central maximum and the mth one and L is the distance of the screen from the grating

    3. The attempt at a solution

    I tried plugging the variables into the equation but I can't seem to get the right answer.

    ie:
    d(y/L)=m(lambda)
    (1/950000)(.436/1)=1lambda
    lambda=460nm which is wrong

    What am I doing wrong?
     
  2. jcsd
  3. Apr 13, 2009 #2

    rl.bhat

    User Avatar
    Homework Helper

    0.436/1 is tanθ. Find sinθ
     
  4. Apr 13, 2009 #3
    Thank you. That worked. I can't believe I missed that.
     
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