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Homework Help: Optics, calculating image distance,.given magnification and focal length

  1. Jan 3, 2013 #1
    1. The problem statement, all variables and given/known data
    The image obtained with a converging lens is upright and 3x the length of the object. The focal length of the lens is 20cm. Calculate the object and image distances

    2. Relevant equations

    I have absolutely no idea how to even start this question

    3. The attempt at a solution
    1/object + 1/image = 1/focal (lens equation )
    1/ob + 1/im= 1/20

    M = ob/im ( magnification formula)
    3= ob/im

    I tried solving for each variable but it wasnt working...
  2. jcsd
  3. Jan 3, 2013 #2


    User Avatar
    Homework Helper

    Hi Faria, welcome to PF.

    The magnification formula is wrong, look it after. And then show your work in detail.

    Is the image real or virtual if the image is upright?

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