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!

Find angular seperation of spectral lines with a grating spectrometer

  1. Apr 21, 2009 #1
    1. The problem statement, all variables and given/known data

    find the angular separation between the red hydrogen-alpha spectral line at 656nm and the yellow sodium line at 589nm if the two are observed in third order with a 3500-line/cm grating spectrometer.

    2. Relevant equations
    maximum equation for multi-slit interference
    d sin(theta)=m*lamda

    d=distance between two slits
    m=the interger called the order (bright spots)
    theta=angular seperation

    3. The attempt at a solution

    I tried plugging all of my data into the equation above with d as 1/grading but I'm not sure if this is the right way to go about the problem. I'm not even sure if this is the best formula to use but I cant find any other relevant equations
  2. jcsd
  3. Apr 24, 2009 #2


    User Avatar
    Gold Member

    Welcome to Pf sailfast

    you are correct, your d is 1/3500 to get centimeters per grating. This equation is correct and applies to this problem. Just be careful with your units and 'm'
  4. Apr 24, 2009 #3
    yay! i rock at PHYS
  5. Aug 6, 2009 #4
    I have the same question here. But when I get sin(theta), I get something over 1. That is not possible. Is my equation wrong? Because I am very sure the units I've been using here are correct. I converted everything into meters.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook