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Lensmaker's Formula

  1. Nov 12, 2009 #1
    1. The problem statement, all variables and given/known data
    A lens has a focal length of f=20cm. If an object is at o=50 cm, where is the image?

    2. Relevant equations

    1/f = 1/o + 1/i

    3. The attempt at a solution

    1/20 = 1/50 + 1/i

    5/100 = 2/100 + 1/i

    3/100 = 1/i

    i = 100/3

    I'm not sure how the answer could be 1/20 = 1/50 + 1/(100/3)? What am I doing wrong?
  2. jcsd
  3. Nov 12, 2009 #2


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    Homework Helper

    The answer is i=100/3 cm (i is the image distance). Why do you suspect it's wrong?
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