Question

A person cannot see distinctly objects kept beyond 2m. Which among these lens is useful to correct the defect 

a) – 0.2D 

b) – 0.5 D 

c) + 0.2D 

d) +0.5D?

Answer 1

The person is suffering from Myopia. The lens is concave and its focal length f = – 2m.

P = 1/5 = 1/-2 = -0.5D

So to correct the defect concave lens of 

– 0.5 D power should be used (b).