A person needs a lens of power -5.5 dioptres for correcting his distant vision. For correcting his near vision, he needs a lens of power + 1.5 dioptres. What is the focal length of the required for correcting (i) distant vision, and (ii) near vision ?

Explanation

Power of the lens for correcting distant vision, `P_(1) = -5.5 D`
Power of the lens for correcting near vision, `P_(2) = +15 D`
Focal length for correcting distant vision,
`f_(1) =(1)/(P_(1)) =(1)/((-5.5)D)=-0.181m`