What power contact lens must be used to correct the vision of a nearsighted person whose far point is 40 cm?
A) +4.0 diopters
B) +2.5 diopters
C) -2.5 diopters
D) -3.6 diopters
E) -4.0 diopters

Question

Quizplus · Accepted Answer

The power P of a lens is given by P = 1/f, where f is the focal length in meters. For a nearsighted person, a diverging lens is needed, which has a negative focal length. The far point of 40 cm (0.4 m) is the maximum distance at which the person can see clearly, so the lens must have a focal length of -0.4 m. Thus, P = 1/(-0.4) = -2.5 diopters.

What Power Contact Lens Must Be Used to Correct the Vision