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What is the near-point of the eye-plus-spectacle?

  • Thread starter gungo
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  • #1
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Homework Statement:

A hyperopic eye has a near point of 75 cm. If a lens of power .75 d is placed in front of the eye, what is the near point of the eye-plus spectacle?

Relevant Equations:

P= 1/p + 1/q
I found the power of the eye itself by doing P= 1/.25 m + 1/ -.75 m. I used negative .75 m because the image would be on the same side of the object. I got a power of 2.67 d. The I added that to the .75 d of the lens. Then I used the same equation and did 3.42= 1/.25 m +1/q to find q, and got -1.72 m. However, the answer is 48 cm.
 

Answers and Replies

  • #2
BvU
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Hi,

Where does the 0.25 come from?

What power is really needed for a near point of 0.75 m ?
 
  • #3
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Hi,

Where does the 0.25 come from?

What power is really needed for a near point of 0.75 m ?
I learned in class that 0.25 m was the near point of a normal eye
 
  • #4
BvU
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the near point of a normal eye
So a normal eye has a power of 4 d. But:
This exercise is about a different eye ! Namely, with a power of ...
 

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