A nearsighted person has a far point of 18 cm. What power contact lenses will allow this person to comfortably see distant objects clearly?
A) $+ 0.056$ diopters
B) $- 0.056$ diopters
C) $- 5.6$ diopters
D) $+ 5.6$ diopters

Question

A nearsighted person has a far point of 18 cm. What power contact lenses will allow this person to comfortably see distant objects clearly? 
A) $+ 0.056$ diopters
B) $- 0.056$ diopters
C) $- 5.6$ diopters
D) $+ 5.6$ diopters

Quizplus · Accepted Answer

The power $P$ of the lenses needed can be calculated using the formula $P = \frac{1}{f}$, where $f$ is the focal length in meters. For a nearsighted person to see distant objects clearly, the lenses must correct the far point to infinity. The far point of 18 cm (0.18 m) is the maximum distance at which the eye can see objects clearly without correction. Thus, $f = -0.18$ m (negative because the lens must diverge the light rays). Therefore, $P = \frac{1}{-0.18} = -5.56$ diopters, which rounds to $-5.6$ diopters. Negative diopters indicate a lens that corrects for nearsightedness by diverging the light rays before they enter the eye.

A Nearsighted Person Has a Far Point of 18 Cm +0.056+ 0.056+0.056

A Nearsighted Person Has a Far Point of 18 Cm $+ 0.056$