1. Not finding help here? Sign up for a free 30min 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!

Double-Slit Arrangement With Plastic Sheet

  1. Nov 29, 2012 #1
    1. The problem statement, all variables and given/known data
    Consider the double-slit arrangement shown in the figure below, where the separation d is 0.280mm and the distance L is 1.16m. A sheet of transparent plastic (n = 1.50) 0.0513mm thick (about the thickness of a piece of paper) is placed over the upper slit. As a result, the central maximum of the interference pattern moves upward a distance y'. What is y'?


    2. Relevant equations
    PD / d = xL
    n = c/v


    3. The attempt at a solution
    I'm sorry. but I have absolutely no idea how to approach this. I've just been looking through my books and trying to find equations to plug the given information into, but no dice. Any help would be greatly, greatly appreciated. Thank you so much!
     
  2. jcsd
  3. Nov 29, 2012 #2
    The presence of the plastic sheet results in a additional phase shift of the light passing through the upper slit relative to the light passing through the lower slit.
    This means that their phase difference has now changed.
     
  4. Nov 29, 2012 #3
    How would I go about calculating that phase difference? Should I use the general wave equation?
     
  5. Nov 29, 2012 #4

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    The plastic adds to the effective path length (refractive index of plastic - index of air)*thickness.
     
  6. Nov 29, 2012 #5
    When the light waves travel through an optically denser medium, they are slowed down - and so they travel more "cycles" (ie oscillate more cycles) in passing through that medium as compared to travelling the same distance in air.
    Say I have two light waves initially in phase. One travels a distance L through air. The other travels the same distance L, but through a medium of refractive index n > 1. The effective optical length travelled by the second wave is in fact nL, and so there is a path difference of (nL-L) between the two waves.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Double-Slit Arrangement With Plastic Sheet
  1. Double slits (Replies: 7)

  2. Double slit (Replies: 2)

Loading...