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Total Internal Reflection a doubt?

  1. Jun 24, 2012 #1
    I was reading about a case of total internal reflection in mirrors and something got me curious...
    Is there anything such as 'weak refractions'??
    In the diagram of the mirror I saw, as a ray of light from an object entered a mirror, it was reflected by the silver coating, and then by the surface of the mirror (assuming it's because of total internal reflection). This process was repeated three times more, and the light ray emerged out of the mirror.
    The doubt I have here is, everytime the ray of light was reflected off from the surface of the mirror (total internal reflection), there was a ray of light exiting the mirror at that point. Where exactly did that ray of light come from?

    Plus, if I may ask further, how many times will total internal reflection have taken place in the above situation?
     
  2. jcsd
  3. Jun 24, 2012 #2

    CWatters

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    I believe the example you are looking at is demonstrating "partial internal reflections" not "total internal reflections".

    See the diagram below (from.. http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/totint.html).

    On the left the angle of incidence is such that the light is partly relected and partly refracted.

    As the angle changes there is a point at which the light that emerges is refracted along the surface. This is called the critical angle.

    On the right the angle is such that the light is totaly reflected and no light emerges.

    totint2.gif
     
    Last edited: Jun 24, 2012
  4. Jun 24, 2012 #3

    CWatters

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    I make the sequence..

    A refraction
    A reflection off the silvered surface
    A partial internal reflection (some light emerges)

    This is then repeated three more times..

    A reflection off the silvered surface
    A partial internal reflection (some light emerges)
    A reflection off the silvered surface
    A partial internal reflection (some light emerges)
    A reflection off the silvered surface
    A partial internal reflection (some light emerges)

    Because the very last reflection is partial there will be a faint emerging ray which is the one you describe as leaving the mirror.

    In the real world you would probably get a lot more internal reflections because mirrors have parallel surfaces. That means once the ray is bouncing around between the surfaces the angle of incidence doesn't change much so there is nothing but the edge of the mirror to stop internal reflections. That's more or less how crude fiber optic cables work.
     
  5. Jun 30, 2012 #4
    My thanks to CWatters :)
    So this is an example of partial internal reflection isn't it??
    I was confused because the heading was written as total internal reflection..zz
    It's been a great help xD Thank you!
     
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