1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    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 Problem, Calculate Slit Width

  1. May 5, 2013 #1
    1. The problem statement, all variables and given/known data

    Light of wavelength 680nm falls onto a single slit. The diffraction pattern is observed on a screen 50cm away. If the distance between the first and the third minima is 3mm, calculate the slit width?

    2. Relevant equations

    sin thetha = m*lambda/a
    y = m*lambda*R/a

    3. The attempt at a solution

    So the distance between the first position and last position of the dark band is 3mm?

    I think this is wrong:

    3*10^-3 = (3)(680*10^-9)(0.5)/a
    a = 3.4*10^-4 m
  2. jcsd
  3. May 5, 2013 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    There are a couple of issues with your attempt.

    1. It looks like you have inserted an extra factor of 0.5 for no apparent reason.

    2. Without the 0.5, the formula gives the spacing between the 3rd minimum and the central maximum.
    However, the 3 mm given in the problem statement refers to the spacing between the 3rd minimum and the 1st minimum. So you need to bring the 1st minimum (n=1) into the picture.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted

Similar Threads - Diffraction Problem Calculate Date
Single-slit Diffraction Problem Aug 12, 2017
Diffraction grating problem May 15, 2017
Double slit problem with glass block Jan 30, 2017
Diffraction problem about calculating the image on the screen Feb 12, 2012