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Homework Help: Elementary Corrective Lens Problem

  1. Apr 17, 2009 #1
    1. The problem statement, all variables and given/known data

    A farsighted woman breaks her current eyeglasses and is using an old pair whose refractive power is 1.655 diopters. Since these eyeglasses do not completely correct her vision, she must hold a newspaper 39.4 cm from her eyes in order to read it. She wears the eyeglasses 1.90 cm from her eyes. How far is her near point from her eyes?

    2. Relevant equations

    1/f = 1/(do) + 1/(di)

    di < 0 for virtual images (what this is)

    3. The attempt at a solution

    do is .394m and 1/f=1.655 diopters

    so 1/(1/.394m - 1.655) = di

    di = 1.13m

    Near Point = 1.13m + .019m = 1.15m

    Where did I go wrong? Thanks!
  2. jcsd
  3. Apr 18, 2009 #2


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    Homework Helper

    Hi EsimatedEyes,

    What is the variable do? It is called the object distance, but what is it? In particular, what two points is it measured between? Once you answer that, I think you'll see what do needs to equal here.
  4. Apr 18, 2009 #3
    I just figured out that the distance was from the lens so I kept getting it wrong because I was using the eyes value that they gave.
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