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A farsighted person has a near point that is 48.0 cm from her eyes. She wears eyeglasses that are designed to enable her to read a newspaper held at a distance of 27.0 cm from her eyes. Find the focal length of the eyeglasses, assuming each of the following.
(a) that they are worn 2.0 cm from the eyes
cm

(b) that they are worn 3.0 cm from the eyes
cm

Submitted: 205 days and 20 hours ago.
Category: Homework
Value: $9
Status: CLOSED
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Expert: Elizabeth
Pos. Feedback: 100.0 %
Accepts: 56
Answered: 7/18/2009

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teaching and tutoring high-school and college mathematics

204 days and 22 hours ago.

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I tried plugging these answers in but they are also wrong.. I understand how you got the answers but don't you have to use the cm that the glasses are worn from the eyes..

Posted by Elizabeth 204 days and 22 hours ago.

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Posted by Elizabeth 204 days and 19 hours ago.

Info Request

Upon closer examination, I see that, while I did the one subtraction correctly, I omitted the other. The corrected values are:

d_i = -48 - (glasses distance)

d_o = 27 - (glasses distance)

a) f = (-46*25)/(25 - 46) = 54.76190476...

focal length: 55 cm

b) f = (-45*24)/(24 - 45) = 51.42857143...

focal length: 51 cm


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