Question

A person cannot see distinctly objects kept beyond 2 m. This defect can be corrected by using a lens of power

Options

• + 0.5 D

• – 0.5 D

• + 0.2 D

• – 0.2 D

Answer 1

– 0.5 D

Explanation - 

The person is suffering from myopia. He needs a concave lens and hence power would be negative.

Object distance, u = - ∞

Image distance,  υ = -2 m

Using lens formula

`1/upsilon - 1/"u" = 1/"f"`

`1/f = 1/(-2) - 1/∞`

f = -2 m

`P = 1/f = -1/(2  "m") = -0.5  "D"`