A person can see clearly only upto 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, `-1.0D`
B. Convex,`+1.5D`
C. Concave, `-2.0D`
D. Convex, `+2.0D`

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)=(1)/(f)=(1)/(-25)-(1)/((-50))impliesf=-50cm`
So power `P=(100)/(f)=(100)/(-50)=-2D`