A nearsighted person wears contact lenses of refractive power $-6.0 \mathrm{D}$. What is his far point?
A) $-17 \mathrm{~cm}$
B) $-6.0 \mathrm{~cm}$
C) $6.0 \mathrm{~cm}$
D) $-4.0 \mathrm{~cm}$
E) $17 \mathrm{~cm}$

Question

Quizplus · Accepted Answer

The far point of a nearsighted person is the maximum distance at which they can see objects clearly without correction. The refractive power of the lenses needed for correction is given by $P = -\frac{1}{f}$, where $P$ is the power in diopters and $f$ is the focal length in meters. Given $P = -6.0 \mathrm{D}$, we find $f = -\frac{1}{6} \mathrm{m} = -16.67 \mathrm{cm}$, which is approximately $17 \mathrm{cm}$ but as a positive distance, since the far point conceptually refers to a positive distance in front of the eyes.

A Nearsighted Person Wears Contact Lenses of Refractive Power −6.0D-6.0 \mathrm{D}−6.0D

A Nearsighted Person Wears Contact Lenses of Refractive Power $-6.0 \mathrm{D}$