Question

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

Answer 1

i) Lens required for correcting

distant vision = – 5.5

Focal length of lens F = \(\frac{1}{P}\)

F = \(\frac{1}{-5.5}\) = 0.181 m

Lens required for correcting this defect = -0.181 M

ii) Lens required for correcting near vision = + 1.5D

Focal length of lens F = \(\frac{1}{P}\)

F = \(\frac{1}{1.5}\) = 0.667 m