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Geometric Optics

  1. Apr 20, 2017 #1
    1. The problem statement, all variables and given/known data
    A farsighted boy has a near point at 2.3 m and requires eyeglasses to correct his vision.

    Corrective lenses are available in increments in power of 0.25 diopters. The eyeglasses

    should have lenses of the lowest power for which the near point is no further than 25

    cm. The correct choice of lens power for eyeglasses, in diopters, is:

    2. Relevant equations
    1/s + 1/s' = 1/f
    1/f = P

    3. The attempt at a solution
    I keep getting a value of 3.57 diopters, however, the correct answer is 3.75.
  2. jcsd
  3. Apr 20, 2017 #2


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    Gold Member

    3.57 diopters does not exist as a choice. :rolleyes:
  4. Apr 20, 2017 #3
    Wonderful... Can you shed some light on the increment and its relation to the correct answer of 3.75?
  5. Apr 20, 2017 #4


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    Staff: Mentor

    You already answered this by yourself!
    Ergo: you have to chose between 3.5 and 3.75. Now you have to calculate which distance at diopters of 3.5 or 3.75 fulfills the requirement "near point no further than ..."
  6. Apr 20, 2017 #5
    Errm. So based off the given answers, which ever is closest to to my value an estimated value of 0.25 increment? Gotcha! Thank you for your response.
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