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!

Homework Help: Dispersion by diffraction grating

  1. Nov 25, 2009 #1
    1. The problem statement, all variables and given/known data

    White light containing wavelengths from 396 nm to 756 nm falls on a grating with 7300 lines/cm. How wide is the first-order spectrum on a screen 2.15 m away?

    2. Relevant equations

    3. The attempt at a solution
    using the equation I have found y1 to be 62.149 and y2 118.635. I took the difference of the two which gave me 56.486 cm, but that is wrong for some reason. Please help.
  2. jcsd
  3. Nov 25, 2009 #2
    Are you sure of that that's the equation for diffraction? Checking the units, it's quite inconsistent... Check the equation again...
  4. Nov 25, 2009 #3
    That's the equation I'm used to. If we assume that the angle is small then sintheta=y/L
    m*wavelength*L/(d)=y ? I don't know what's wrong with the equation. For the units I coverted everything to cm because 1/7300=d in cm.
  5. Nov 25, 2009 #4
    Please help, I only have a couple of hours left.
  6. Nov 25, 2009 #5
    I got 56.502 cm, using the equation. we seem to get the same answer.
    Last edited: Nov 25, 2009
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook