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    Morning,

    I’m franticly revising for AQA Physics Unit 2 tomorrow afternoon. It was going ok until I came across diffraction grating. I under stand the formula. But when coming to use it I come unstuck of how to interpret d (grating spacing) Here is an example

    A Laser beam of wavelength 630 nm is directed normally at a diffraction grating with 300 lines per mm. Calculate … the angle of diffraction on the first order.

    So its 690*10^-9 for wavelength into meters however, for the grating spacing how would I work out the correct value for d ?

    The book says 1/d, but I always seem to be getting the wrong answer. If someone could please highlight my fault it would be much appreciated.
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    300 lines per mm does indeed give the spacing by taking the inverse. (1/lines per m)
    The usual thing that causes errors is mixing up the units. There are nm, and mm here.
    Convert all to metre. 300 lines per mm is 300 x 1000 lines per metre as there are 1000 mm in a metre. (=3 x 10^5)
    1 over this then can be used with 690 x 10^-9 m for wavelength.
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    Brilliant. Thanks for the help.
 
 
 
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Updated: January 17, 2010
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