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Homework Help: Finding Size of Candle

  1. Mar 31, 2010 #1
    1. The problem statement, all variables and given/known data
    A candle is placed 10 inches from a convex lens whose focal length is 5 in. Where will the image be formed? How large an image is formed?

    2. Relevant equations

    3. The attempt at a solution
    Here we use the following formula to find where the image will be formed:
    1/f=1/Do+1/Di  1/Di=1/f-1/Do =
    1/Di=1/5-1/10 = 2-1/10 = 10 in.

    Here's the equation to solve part B but I don't know how to figure "So" which would be dimensions of the candle. Any help?

    Si=So(Di/Do) =
    Si=So(10/10) =
  2. jcsd
  3. Mar 31, 2010 #2
    Well you can't give a numerical answer but you can say that the image formed is the same height as the object.
  4. Apr 1, 2010 #3

    So, there's no numerical way to solve without being given the height of the object?
  5. Apr 1, 2010 #4
    Nope, because that would mean that the image height does not depend on the object height which is clearly not true.
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