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Homework Help: Focal length of lense

  1. Nov 14, 2008 #1
    1. The problem statement, all variables and given/known data
    The nickel's image in the figure below has twice the diameter of the nickel when the lens is 2.90 cm from the nickel. Determine the focal length of the lens.

    2. Relevant equations

    M = h'/h = - (p/q)

    3. The attempt at a solution
    i dont really know how to start this one... eek
  2. jcsd
  3. Nov 14, 2008 #2


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    Staff Emeritus
    Science Advisor
    Homework Helper

    There is a well-known equation for lenses, try that one.

    Hint: it has a "1/f" in it.
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