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Homework Help: Question from an Extras Class.

  1. Jan 25, 2009 #1
    1. The problem statement, all variables and given/known data
    Got some work from my dad, but one question kinda stumped me.

    A short sighted person can view an object clearly only when it is between 11 cm and 19 cm from her eyes. Calculate:
    1. The Focal Length of the specatacles required to give her a near point of 25 cm.


    2. Relevant equations
    I don't know what equation to use here. I usually see questions about image and object distances and object distances using the 1/u+ 1/v= 1/f equation, I've never seen one like this.


    3. The attempt at a solution
    I just assumed, 1/.25 + 1/infinity = 1/f
    1/.25 + 0 = 1/f
    1/.25 = 1/f
    4 = 1/f
    f = 1/4
    f= .25
     
  2. jcsd
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