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Homework Help: Diffraction Grating Problem, brightness maximum involved

  1. Mar 12, 2009 #1
    1. The problem statement, all variables and given/known data
    A bulb emits a continuous spectrum of ultraviolet, visible and infrared light in the wavelength range 360nm to 2000nm. Assume that the light from this bulb is incident on a diffraction grating with slit spacing d and that the first-order brightness maximum for the wavelength of 1200 nm occurs at angle (theta). What other wavelengths within the spectrum of incident light will produce a brightness maximum at this same angle (theta)?

    2. Relevant equations
    sin(theta) = m(lamda)/d
    where m is an integer representing the order, and d is the distance between grating lines. Lamda represents the wavelengths of the light.

    3. The attempt at a solution
    Since I am given a lamda (wavelength) and an order, I set up my equation for theta as
    (theta) = arcsin (1200nm/d)
    I have no idea what the problem is asking for.
    Please give me some hints.
  2. jcsd
  3. Mar 12, 2009 #2
    Are you familiar with the geometry, what d , theta are? that really helps thinking these through.
    otherwise, "first-order" refers to m=1 in that equation for the location(theta) of brightness maxima.
    The question should make sense now.
  4. Mar 12, 2009 #3
    I went back to look in my textbook, but I am still confused by what you mean. I know that d is the separation between slits, D is the actual width of each slit, and theta is the angular spread. I am still confused however.
  5. Mar 13, 2009 #4
    can u post the figure?
    Otherwise, that m(lambda) is just the requirement to get constructive interference. m(lambda) can equal the same number for different combinations of m and lambda...
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