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Homework Help: Virtual boxes mirror reflection

  1. Nov 14, 2013 #1
    1. The problem statement, all variables and given/known data

    Finding lightpaths with given starting and ending points via one or more mirrors.

    In those kind of problems you try image someone pointing a laser with a very narrow beam at a certain direction to the mirror, so it will reach point B.

    For example:

    You are seeing a square mirror room (with mirrorwalls a, b​​, c, d) where you point from point A via the mirrors c, b, d and a to point B. A sketch can be made easily made.


    In order to find a more accurate solution, we flip the base cell with the points A and B
    a few times as shown in the image.
    After the mirroring is done, the line connecting A is drawn towards the mirror image B '.
    Question: Construct the path in the original square.
    Complete the drawing.


    2. Relevant equations

    mirror images

    3. The attempt at a solution

    What do I need to do with those virtual squares? And why is the line drawn from A to B' through those other rooms?
    Last edited: Nov 14, 2013
  2. jcsd
  3. Nov 14, 2013 #2


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    Staff: Mentor

    The drawing looks quite complete to me...

    Mirrors do exactly what those virtual boxes represent: They show a "mirror world", like the box above your real box. That is not limited to a single mirror, you can fill the whole grid with those mirror images.
    There are mirror arrangements where this is not helpful, but with a quadratic box it is nice.
  4. Nov 14, 2013 #3
    I guess there suppose to be lines in other virtual boxes.
  5. Nov 15, 2013 #4


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    Staff: Mentor

    Then you can draw those lines. There is an infinite number of them, so I guess you have to restrict yourself to a few of them.
  6. Nov 15, 2013 #5


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    Gold Member

    This is a way of working out where the image appears to be to an observer..

    If you stood at point A in the original cell and looked in the direction of the laser beam you would see point B but it would appear to you as if it was at point B'.
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