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 37.0 cm and -1.80 m from the eye. (a) The upper portions of the bifocals (see figure above) should be designed to enable her to see distant objects clearly. What power should they have? -0.55 diopters (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? 1.142 Your response differs from the correct answer by more than 10%. Double check your calculations. diopters

Explanation / Answer

A. Power (diopters) = 1/f
f = -1.8 m; power = 1/-1.8 = -0.55 diopters.
B. By "comfortably" I assume the desire is to have her eyes relaxed, i.e., focused on what would be 1.8 m without glasses.
power = 1/-1.8 + 1/0.25 = 3.44 diopters.
If instead the desire is to focus at 0.25 m as her minimum distance,
power = 1/-0.37 + 1/0.25 = 1.30 diopters

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