1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Diffraction of light question

  1. May 7, 2008 #1
    1. The problem statement, all variables and given/known data
    How many orders of diffraction will be visible if light of wavelength 500nm fals on a grating with 600 000 lines per metre?

    2. Relevant equations

    n = dsinѲ / λ

    3. The attempt at a solution

    n = 6X10⁵m ÷ 5 X 10ˉ⁷m = 1.2
    So 1 order of diffraction will be visible is this right??

    I don't have the angle so I could put it into the equation.
    Last edited: May 7, 2008
  2. jcsd
  3. May 7, 2008 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    Note that d is really (1/600,000) m, so that 600,000 lines would fit in 1 m.
  4. May 7, 2008 #3
    Another way to pose this question is: how many maxima do you see between theta=0 and theta=90 degrees?

    Consider that for a maximum to appear on the wall or the screen in front of the grating the angle theta can never be more than 90 degrees. (Recall that sin(theta) ~ (distance of nth maxima from the 0th maxima)/(distance of the grating from the screen).)
  5. May 8, 2008 #4
    Thanks for your help. Here is my improved answer:
    λ = 500nm = 5 X 10ˉ⁷m
    d = 6 X 10⁵ per metre = 1 ÷ 6 X 10⁵ = 16.7 X 10ˉ⁷m
    n = 16.7 X 10ˉ⁷ X sin 90 ÷ 5 X 10ˉ⁷ = 3.34
    There will be 3 orders of diffraction visible

    Is this correct? If not please tell me where I am going wrong

  6. May 8, 2008 #5


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    Looks good. Problem solved :smile:
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook