A person is to be fitted with bifocals. She can see clearly when the object is b

Question

A person is to be fitted with bifocals. She can see clearly when the object is between 38.0cm and 1.0m from the eye. Since the upper portion of the bifocals should be designed to enable her to see distant objects clearly, what is the power they should have (in diopters)? (Assume there is no significant distance between the eye and the glasses lens.) Submit AnswerTries 0/10 The lower portion of the bifocals in the question above should enable her to see objects comfortably at 25.0cm. What power should they have (in diopters)? Submit Answer Tries 0/10

Explanation / Answer

A.

Power (diopters) = 1/f

f = -1.0 m; power = 1/-1.0 = -1.0 diopters.

B.

By "comfortably" I assume the desire is to have her eyes relaxed, i.e., focused on what would be 1.0 m without glasses.

power = 1/-1.0 + 1/0.25 = 3.0 diopters.

If instead the desire is to focus at 0.25 m as her minimum distance,

power = 1/-0.38 + 1/0.25 = 1.3684 diopters (ans)

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