The near point of a farsighted person's uncorrected eyes is 80 cm.What power contact lens should be used to move the near point to 25 cm from this person's eyes?
A) 2.8 diopters
B) -2.8 diopters
C) -4.0 diopters
D) -4.2 diopters
E) 4.2 diopters

Question

Quizplus · Accepted Answer

To find the power of the lens needed, use the lens formula: 1/f = 1/v - 1/u. Here, v = -25 cm (since the image should form at the near point of 25 cm) and u = -80 cm (the original near point). Solving gives 1/f = 1/(-25) - 1/(-80) = 0.028 diopters, which is approximately 2.8 diopters.

The near Point of a Farsighted Person's Uncorrected Eyes Is