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Unpolarized light

  1. Jan 1, 2012 #1
    Hello, I am reading an intro book on optics and it is discussing the polarization of light and unpolarized light. My question is with unpolarized light I quote:

    "This sinusoidally varying electric field can be thought of as a length of rope held by two children at opposite ends. The children begin to displace the ends in such a way that the rope moves in a plane, either up and down, left and right, or at any angle in between."

    So with this in mind I think well if most light is naturally unpolarized then wouldn't a mix of all of the different angles eventually end up cancelling each other out? I'd like to think of polarized light as coming in two orthogonal basis and then all others combinations of the two, are all polarized light vectors the sum of basis components like force vectors? I'm still beginning so I appreciate the input.
  2. jcsd
  3. Jan 1, 2012 #2
    not sure if this should be in homework or not so mods please feel free to delete where necessary
  4. Jan 2, 2012 #3


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    I think kids jumping rope are more compllicated than a simple picture of the E field.
    Unpolarized light would be like millions of kids and ropes, each at a different random angle.
    These ropes do not cancel each other.
  5. Jan 2, 2012 #4
    Your concept is generally ok but light is different:

    Natural light, like from the sun or even a lightbulb, is typically unpolarized....but light is a transverse wave not a longitudional wave like a rope....so the example in your book is a bad model:
    see here:


    Scan down the article and note the illustrations, some animated, for a better view of polarization.

    " The two waves must have the same polarization to give rise to interference fringes since it is not possible for waves of different polarizations to cancel one another out or add together. Instead, when waves of different polarization are added together, they give rise to a wave of a different polarization state."

    Last edited: Jan 2, 2012
  6. Jan 2, 2012 #5
    A wave in a rope is a transverse wave, if you hold the end and move the end in a reciprocating action at 90 degrees to the rope you will create a transverse wave along the rope.
  7. Jan 2, 2012 #6
    This is exactly what I needed! Thanks
  8. Jan 2, 2012 #7
    I recall an experiment the kids would do on polarized light. They would place a large piece of cardboard with a slit in it large enough to allow the wave to pass through it - in other words large enough to exceed he amplitude of the typical wave that is to be generated. The slip was placed so it was vertical. The students shook the spring or rope and created standing waves by shaking the rope vertically also. They saw that the wave passed throught the slit easily. They then created a transverse wave by shaking the rope sideways. When the wave hit the slit which was still vertical, from the side, it did not pass through. If they tried to shake the rope and produce waves diagonally they notice that the wave did pass through the slit but had a lower amplitude on the other side meaning part of the wave energy was blocked.

    So they then looked at some light through polarizing filters and noticed that indeed not all the light went through the filters, but some did. And the light that made it through was now "polarized". or moving up and down in a common plane just as their waves on the rope did.
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