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Homework Help: Physics-Young's Double Slit Problem

  1. Sep 29, 2006 #1
    Hello! I am stuck on a problem that seems so easy. The question is:

    Two slits are 0.143 mm apart. A mixture of red light (wavelength = 665 nm) and yellow-green light (wavelength = 565 nm) falls on the slits. A flat observation screen is located 2.29 m away. What is the distance on the screen between the third-order red fringe and the third-order yellow-green fringe?

    I solved for Theta for both red light and the yellow-green light. (m = 3)

    Theta = sin-1((m*lamda) / d)

    Red: Theta = sin-1((3 * 665e-9) / .143e-3) = .799 degrees

    Yellow-green: Theta = sin-1((3 * 565e-9) / .143e-3) = .679 degrees

    From there I solved for the distance and subtracted the two:

    y = L * tan theta

    Red: y = 2.29 * tan(.799) = 0.032m

    Yellow-green: y = 2.29 * tan(.679) = 0.027m

    I get an answer of 0.005m but the site says my answer is wrong. Any hints as to what I am doing wrong?

    Thank you for any help!!
  2. jcsd
  3. Sep 29, 2006 #2
    try inputting your answer to the same degree of accuracy as the slit seperation, try 4.804 mm
  4. Oct 1, 2006 #3
    Thank you! It had to be in meters so it took 4.804e-3 meters! I am glad it was an easy fix. I thought I had a grasp of this concept and I was frustrated when I couldn't get the correct answer.

    Thank you again!!!
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