A person is suffering from myopic defect. He is able to see clear objects placed at `15 cm`. What type and of what focal length of lens he should use to see clearly the object placed `60 cm` away ?

Options

A. Concave lens of `20 cm` focal length
B. Convex lens of `20 cm` focal length
C. Concave lens of `12 cm` focal length
D. Convex lens of `12 cm` focal length

Answer

A

Explanation

For viewing far objects, concave lenses are used and for concave lens
`u=` wants to see `=-60cm,v=` can see `=-15 cm`
so from `(1)/(f)=(1)/(v)-(1)/(u)impliesf=-20cm.`