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Homework Help: Equation for object size relative to reflection?

  1. Sep 7, 2013 #1
    1. The problem statement, all variables and given/known data

    The situation below is based upon the image of an object in the presence of a sheet with a small hole and an object that reflects an image onto a screen when shined with a light. The problem is below:

    Write an equation that shows the relationship between the length of an object, the distance of the object from a sheet with a small hole, the length of the object's image on a screen, and the distance of the sheet to the screen.

    2. Relevant equations

    I'm not sure what equations would be relevant for this situation...

    3. The attempt at a solution

    See attached document. Any help with determining the equation would be appreciated.

    Attached Files:

  2. jcsd
  3. Sep 8, 2013 #2

    rude man

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    Gold Member

    Just draw the situation onto paper. Use ray optics.
    This used to be called a pinhole camera or camera obscura. Try it yourself sometime!
    Same principle as why people squint to see better ...
  4. Sep 8, 2013 #3


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    Staff Emeritus
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    That is what Violagirl has already attempted, in the figure attached to her post.

    Violagirl, notice that the problem statement said "a small hole". But the hole in your figure is nearly the size of the object. I would redraw your figure, with the hole very small -- you could just use a small dot to represent the hole.

    Then, redraw the rays from the object to the screen.

    (Also, those rays you drew to the left of the object are not really needed.)

    Hope that helps.
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