A person needs of power -4D for correcting his distant vision. For correcting his near vision he needs a lens of power + 1.5 D . What is focal length of the lens required for correcting?
(i) Distant vision (ii) Near vision ?

Explanation

Given ,P=-4D
To find : Focal length of the lens , `f=?`
For correct real vision , `f=?`
`P=1/f`
`therefore f =1/P implies 1/(-4)`
(i) f=-0.25 m
P= +1.5 D
`P=1/f`
`therefore f =1/P implies f= 1/(1.5) `
(ii) Focal length of correcting , f=+0.667 m