Question

A person needs a lens of power -6.0dioptre for correcting his distant vision. For correcting his near vision, he needs a lens of power +2.0 dioptre. What is the focal length of the lens and its nature required for correcting (i)distant vision (ii)Near vision

Answer 1

Power =100\f (when f is in cm)
- 0.6 = 100\f
so,
f = -1.6 metre , that is , convex lens .
and in second case ,
2 = 100\f
f = 1\2 metre , that is , concave lens .