Sometimes a person cannot clearly see objects close up or far away. To correct t
ID: 1403218 • Letter: S
Question
Sometimes a person cannot clearly see objects close up or far away. To correct this type of vision, bifocals are often used. The top half of the lens is used to view distant objects and the bottom half of the lens is used to view objects close to the eye. A person can clearly see objects only if they are located between 35 cm and 170 cm away from her eyes. Bifocal lenses are used to correct her vision. What power lens (in diopters) should be used in the bottom half of the lens to allow her to clearly see objects 25 cm away?
A: -2.86 B: -1.14 C: -0.59 D: -0.49 E: 0.49 F: 0.59 G: 1.14 H: 2.86Explanation / Answer
Since the lens allow her to see clearly the object at distance 25 cm therefore
u = - 25 cm
And eye can see clearly at 35 cm therefore
v = -35 cm
so from lens equation
1/f = 1/v - 1/u
f = 87.5 cm = 0.875 m
Power = 1/f = 1.14
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