An elderly person's range of vision is between 70 cm and 300 cm from the eye.What focal length lens is needed to allow her to read a newspaper clearly at the normal distance of 25 cm from her eyes?
A)38.9 cm
B)18.4 cm
C)27.3cm
D)23.1 cm
E)70.0 cm

Question

Quizplus · Accepted Answer

The correct answer is A because the focal length of the lens is given by the formula 1/f = 1/v - 1/u, where f is the focal length, v is the image distance, and u is the object distance. In this case, the image distance is 25 cm and the object distance is 70 cm, so the focal length is 38.9 cm.

An Elderly Person's Range of Vision Is Between 70 Cm