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Math Help - Number of diffracted orders produced

  1. #1
    Member
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    Number of diffracted orders produced

    Hi
    A liitle help will be appreciated. The question is as follows:
    A laser beam of wavelength 630nm is directed normally at a diffraction grating with 300 lines per millimetre. Calculate:
    a) The angle of diffraction of each of the first 2 orders
    b) The number of diffracted orders produced
    Solution
    I used the formula
    d X sintheta = n x wavelength
    N= 300000
    therefore d= 1/300000
    n=2
    Wavelength = 630nm
    Putting the above value in I obtained 22 .2 degrees
    b) For the second part, I surmised that theta = 90 degrees
    Therefore,
    n = d/wavelength
    I obtained 5. 29. But this diifers from the books answer.
    Please help!
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  2. #2
    MHF Contributor Unknown008's Avatar
    Joined
    May 2010
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    Mauritius
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    1,260
    a) The question asks you for the angle for the first 2 orders, meaning the 1st order of diffraction and the 2nd order of diffraction, not the 2nd order alone.

    The angle for the second order is good.

    b) Right, you have 5 orders below the 0 order diffraction. Therefore, you also have 5 orders above the 0 order diffration, for a total of 5 + 1 + 5 = 11 diffraction orders.
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