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Homework Help: Lenses with eyes

  1. Feb 7, 2010 #1
    The focal length of a relaxed human eye is approximately 1.78 cm. When we focus our eyes on a close-up object, we can change the refractive power of the eye by about 16 diopters. Calculate the focal length of the eye when we focus closely.


    im not really sure what to do with the diopters. please help me start the problem.
  2. jcsd
  3. Feb 7, 2010 #2
    A diopter is 1/f measured in meters. So 16 diopters would be 1/16 meters.
  4. Feb 7, 2010 #3
    alright so the 1.78 cm needs to be changed to .0178 m. do i need to incorporate that equation somehow or is this a really simple problem?
  5. Feb 8, 2010 #4
    someone please help. this homework is due tonight and i dont know where to go from here
  6. Feb 8, 2010 #5


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    Hope this isn't too late.

    A 16 diopter change means the following:
    The value of 1/f is changed by 16/m or 16 m-1
    You just need to figure out if 1/f would get larger or smaller, given that the eye is focusing on something close up.
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