The greatest distance a person can see an object in focus is 35.0 cm in front of his eyes.What power of eyeglasses should he wear in order to see distant objects clearly? His eyeglasses sit 2.0 cm in front of his eyes.
A)-3.03 D
B)-2.86 D
C)+2.86 D
D)+3.03 D
E)None are correct.

Question

Quizplus · Accepted Answer

The power $P$ of the eyeglasses needed can be calculated using the lens formula, where $P = 1/f$, and $f$ is the focal length in meters. The person's far point is 35.0 cm (0.35 m) from his eyes, but since the glasses will sit 2.0 cm (0.02 m) in front of his eyes, the effective distance to the far point becomes 0.35 m - 0.02 m = 0.33 m. Thus, $f = 0.33 m$, and $P = 1/0.33 \approx 3.03$ diopters. Since the person is nearsighted and needs to bring distant objects into focus, the lenses must be diverging, which means they should have a negative power. Therefore, the correct answer is -3.03 D.

The Greatest Distance a Person Can See an Object in Focus