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University of Wisconsin - Milwaukee

A person is to be fitted with bifocals. She can see clearly when the object is between 30. cm and 1.5 m from the eye. (a) The upper portions of the bifocals (Fig. P25.18) should be designed to enable her to see distant objects clearly. What power should they have? (b) The lower portions of the bifocals should enable her to see objects located 25 cm in front of the eye. What power should they have?

a. -0.667 \text { diopters }b. +0.667 \text { diopters }

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Elyse G.

Cornell University

Other Schools

Aspen F.

University of Sheffield

Video Transcript

in this problem. A person's near point is 30 centimeter and Farpoint is 1.5 meter. So for part A, as shown in the figure upper portion of the bicycle, should be enable for her to see the distant objects. To do that, the upper portion let's should be adjusted so that virtual a pride in his chute form at her Farpoint. So when she looks at the distant objects, then for P, he calls infinity, which is distant object Q has to be called in for collect, which is the Farpoint Negative. Farpoint, I should remind you again this negative assignments are pride. Unfortunately, ms So from here the power is basically P equals one over F in meters and that's gonna be won over negative 1.5 in meters. And this will give us negative 0.67 Diop tres So now for part B. If she wants to be able to see an object, a 25 centimetre than the lower person of the lens must form a virtual apartment of her near point. So that means if p e cause 25 centimeter, which is 0.25 meter, then Q has to be at near point which is negative 30 centimeter and that also means zero point negative 0.3 meter. So from here we can just write down the definition of the power. P equals won over F in meters which is going to be won over P plus one of her cue and this is going to be a queue plus P over Q minus P. Sorry, two times p so and the queue is negative. 30 which is negative. 0.3 plus p is 0.25 over negative, 0.3 times 0.25 So this will give us positive 0.67 doctors, which is the power for the lower person of the men's.

University of Wisconsin - Milwaukee
Elyse G.

Cornell University

Other Schools

Aspen F.

University of Sheffield