A writer uses a converging lens of focal length f 16 cm as

A writer uses a converging lens of focal length f = 16 cm as a magnifying glass to read fine print on his book contract. Initially, the writer holds the lens above the fine print so that its image is at infinity. To get a better look, he then moves the lens so that the image is at his 25-cm near point. In what direction (toward or away from the fine print) did the writer move the lens? How far did the writer move the lens? Assume his eye is adjusted to remain always very near the magnifying glass.

Solution

focal length f = 16 cm

image distance s\' = infinity

object distance should be s = 16 cm

part A

for the image distance to decrease the object distance should increase

toward the fine print-----------ANSWER

part B

from the relation

1/s + 1/s\' = 1/f

1/s + 1/25 = 1/16

s = 44.44 cm

so delta d = 44.44 - 16

delta d = 28.44 cm