# Optics with lenses and eyes

1. Apr 8, 2014

### physicsztudent

1. The problem statement, all variables and given/known data
A farsighted woman cannot see objects clearly that are closer to her eye than 60.0 cm. Determine the focal length and power of the spectacle lenses that will enable her to read a book at a distance of 25.0 cm.

2. Relevant equations
The equation I have been using to find the focal length is: 1/p + 1/q = 1/f

For the magnifying power, I believe that equation is 1/f = P

3. The attempt at a solution

I've been getting stuck after setting p to infinity which my instructor said to do, then I'm left with 1/q = 1/f ... I don't see how that helps me narrow down my attempt in solving the problem. I understand that the woman needs a min of 60 cm length for the image to be perfectly seen in her eye but I'm not seeing how to incorporate the other information presented in the problem.

2. Apr 9, 2014

### ehild

The book is at 25 cm distance from the eye, but the women can see something not closer than 60 cm. If the image of the book is at 60 cm, would she see it? What are the object distance and image distance then? And you can assume that the eye and the lens are at the same place. distance from the eye is the same as the distance from the lens.

ehild

Last edited: Apr 9, 2014
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