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Homework Help: Angular Magnification

  1. Jun 7, 2010 #1
    1. The problem statement, all variables and given/known data
    If you have normal vision and are properly using a magnifying glass with a refractive power of 12.5 diopters, how far should you hold it from the object to achieve maximum angular magnification?

    2. Relevant equations

    1 diopter = 1/focal length = m^-1
    M=angular magnification
    Mmax = [(Near Point)/f] +1
    Near point for someone with normal vision = 25cm

    3. The attempt at a solution

    First I use 12.5 diopters to figure out the focal length:

    1/12.5 = .08m = 8cm
    Then I plugged this into the equation for Mmax for someone with normal vision:
    [25cm / 8cm] + 1 = 4.125 = Mmax

    I don't know how to use any of this to find the maximum distance the object should be held at though. The prof already posted the answers-this should be 6.67 cm- I'm just trying to practice before an exam and learn how to do this, so any help/tips would be great. Thanks!
  2. jcsd
  3. Jun 9, 2010 #2
    Maybe you can use this:

    M = (f-v)/f

    4.125 = 8-v/8

    v = 25cm

    I am not so sure abt the answer. Another formula that you might find useful is M = f/(f+u)
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