Question

If the near point of eyes of a man is 75 cm, then what should be the focal length of the lens if he wants to read the newspaper at a distance of 25 cm?

Answer 1

Here he wants read the newspaper at a distance of 25 cm, hence we have do= 25 cm

do= 25 cm
di=-75 cm
Applying the len's formula; 1/f= 1/di+1/do
1/f= 1/25+1/-75= 0.04-0.013= 0.027
f= 1/0.027= 37.04 cm
Focal length of the lens is 37.04 cm