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Homework Help: Object Distance from Lens

  1. Apr 12, 2009 #1
    1. The problem statement, all variables and given/known data
    An object is in front of a lens with a focal length of -15cm. An image ½ the side of the object is formed. How far is the object from the lens?

    2. Relevant equations
    m - magnification
    q - distance from image
    p - distance from object
    f - focal length

    m = -q/p
    1/p + 1/q = 1/f

    3. The attempt at a solution
    m = -q/p so q = -(1/2)p

    1/p + 1/q = 1/f
    1/p + 1/(-1/2p) = 1/-15cm
    -1/p = 1/-15cm
    p = 15 cm
  2. jcsd
  3. Apr 12, 2009 #2


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    Homework Helper

    Your answer is correct.
  4. Apr 12, 2009 #3
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