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Homework Help: Converging Lens

  1. Apr 3, 2007 #1
    1. The problem statement, all variables and given/known data

    The distance between an object and its image is fixed at 40.0 cm. A converging lens of focal length f = 4.2 cm forms a sharp image for two positions of the lens. What is the distance a between these two positions?

    2. Relevant equations

    1/p + 1/q = 1/f

    3. The attempt at a solution

    I am very confused with this problem and really have no idea where to begin. If anyone can provide some assistance, that would be great. Thanks.
  2. jcsd
  3. Apr 3, 2007 #2


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    Homework Helper

    You have the lens equation. You know f. You also know that p+q=40. So what you have is two equations and two unknowns. Try solving for p (or q) and see what you come up with.
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