A person struggles to read by holding a book at arms length

A person struggles to read by holding a book at arm\'s length, a distance 60 cm away. What power of reading glasses should be prescribed for him assuming that they will be placed 2.0 cm from the eye and he wants to read at the \"normal\" near point of 25 cm?

Solution

Here ,

di = -60 cm

do = 25 cm

let the focal length of lens needed is f

1/f = 1/(-60 + 2) + 1/(25 - 2)

solving for f

f = 38.11 cm

Power = 100/f = 100/38.11

Power = 2.62 D

the power of the reading glases should be prescribed is 2.62 D