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Homework Help: Question on mirror and lens combinations

  1. Apr 15, 2015 #1
    1. The problem statement, all variables and given/known data
    The question is attached in the jpeg file.

    2. Relevant equations
    1/do + 1/di = 1/f

    3. The attempt at a solution
    First reflection : 1/100 + 1/di = 1/80 , di = 400cm ( To the right of the lens )

    This means that the image created is a virtual image since it is behind the lens.

    So for second reflection : -1/300 + 1/di = -1/50 , di = -60cm ( To the right of the mirror )

    The image is virtual , therefore for last reflection : -1/160 + 1/di = 1/80 , di = 53.3cm

    I can't seem to be able to get the answer , if I took the object distance for the last reflection as positive. I do get the answer. But it does not make sense to me.

    I usually have problems with these kind of questions as I'm unsure where is infront or behind the mirror? Is this defined by the original real object that causes the reflections to occur?

    Attached Files:

  2. jcsd
  3. Apr 15, 2015 #2
    Lenses refract light. And for this convex lens, the image formed will be real because the object distance is greater than the focal length.
    Welcome to PF.
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