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Homework Help: Finding the height of an image reflected through a lens?

  1. Sep 20, 2012 #1
    1. The problem statement, all variables and given/known data

    A 2.0--tall candle flame is 2.1 m from a wall. You happen to have a lens with a focal length of 37 cm .

    How many places can you put the lens to form a well-focused image of the candle flame on the wall?

    For each location, what are the height and orientation of the image?

    2. Relevant equations



    3. The attempt at a solution

    So I think there are 2 places you can place the lens because s'+s=210cm and s' and s are interchangeable or something like that. I'm not quite sure though.

    But then for the second part, i found the heights to be .65 and 6.2 cm but either one or both are wrong. I know I have to find the values for s and s' and I'm not quite sure how to do that. I thought s' would just be 2.1 but how can you have two values for it then?
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Sep 20, 2012 #2


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    Homework Helper

    Put s' = 210 - s and substitute it in the lens formula to find s.
  4. Sep 20, 2012 #3
    ah..just realized that myself.
    that's so simple. i was definitely over thinking it.

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