A person can see clearly only up to a distance of `25 cm`. He wants to read a book placed at a distance of `50cm`. What kind of lens does he require for his spectacles and what must be its power ?

Options

A. Concave, `-1.0 D`
B. Convex , `+1.5D`
C. Concave, `-2.0D`
D. Convex, `+2.0 D`

Answer

C

Explanation

For correcting myopia, concave lens is used and for lens.
`u=`wants to see`=-50cm`
`v=`can see`=-25cm,`
`(1)/(f)=(1)/(v)-(1)/(u) rArr (1)/(f)=(1)/(-25)-(1)/((-50))`
`impliesf=-50cm`
So power `P=(100)/(f)=(100)/(-50)=-2D`