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: Fringes from Different Interfering Wavelengths

  1. Apr 3, 2014 #1
    1. The problem statement, all variables and given/known data

    The questions is...
    Coherent light with wavelength 597nm passes through two very narrow slits, and the interference pattern is observed on a screen a distance of 3.00 m from the slits. The first-order bright fringe is a distance of 4.84 mm from the center of the central bright fringe.

    For what wavelength of light will the first-order dark fringe (the first dark fringe next to a central maximum) be observed at this same point on the screen?

    But I am doing something wrong because I keep getting an incorrect answer.
    Any help would be appreciated! Thank you!

    2. Relevant equations

    dsinθ=mλ --constructive interference
    dsinθ=(m+1/2)λ --destructive interference

    3. The attempt at a solution

    I think that I should use the equation for constructive interference: dsinθ=mλ
    And I am pretty sure you can use the approximation that sinθ≈tanθ
    But doing this, and looking at the triangle, I am getting confused as to where to put the values. I think that "m" would be 1, but I am not sure if that is correct.

    I also tried using the third equation: (597E-3)*(3E6)/(4.84E3)=370, but this answer is not correct either.
  2. jcsd
  3. Apr 3, 2014 #2
    Use the constructive interference formula to find d and then use the destructive interference formula to find the new wavelength. There are two separate experiments here.
  4. Apr 4, 2014 #3
    equation you are using is of DIFFRACTION. I think you should use the one of interference , ie,
    ß=λD/d ; ß=fringe width , λ=wavelength,D-distance to screen,d-distance b/w slits.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted