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Homework Help: Optics Experiment

  1. Apr 18, 2009 #1
    1. You are given the following equipment for use in the optics experiments in parts (a) and (b).
    - A solid rectangular block made of transparent plastic
    - A laser that produces a narrow, bright, monochromatic ray of light
    - A protractor
    - A meter stick
    - A diffraction grating of known slit spacing
    - A white opaque screen

    (a) Briefly describe the procedure you would use to determine the index of refraction of the plastic. Diagram?

    (b) Since the index of refraction depends on wavelength, you need to determine the wavelength of your light source.
    2. Dark Slits vs. Bright Slits
    Path Difference: Δl = dsinθ
    Bright Fringe: dsinθ =mλ
    Dark Fringe: dsinθ = (m-1/2)λ

    3. Does this all have to do with Young's Two Slit Experiment? Setting up something that will create an interference pattern and then using that to determine other things..?
  2. jcsd
  3. Apr 18, 2009 #2
    Yes. The equation d*sin(theta) = m*lamda that gives the maxima for Young's experiment is the same equation for a diffraction grating.

    Your problem is to determine the index of refraction of the plastic. Here are some key questions you need to answer. What happens to the wavelength of light when you pass it through some material other than a vacuum? What is the behavior among wavelength and the angles associated with maxima in Young's interference experiment?
  4. Apr 19, 2009 #3


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    Homework Helper

    Using diffraction grating form the interference pattern on the white screen. Mark the central and first order bright spot. Draw a perpendicular from central bright spot to position of the grating. Join the point of intersection of these to to the first order bright spot. That gives you the angle θ. Now place the plastic block in the path of the ray and parallel to the screen. Mark the new position of the first order bright spot. From this point draw a parallel line to the initial path of the ray. Find the distance between them. That is the lateral shift. Find the expression for the lateral from any book and find refractive index of the plastic slab.
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