A man suffering from myopia can read book placed at `10 cm` distance. For reading the book at a distance of `60 cm` with relaxed vision, focal length of the lens required will be

Options

A. `45 cm`
B. `-20 cm`
C. `-12 cm`
D. `30 cm`

Answer

C

Explanation

For lens `u=` wants to see `=-60cm`
`v=`can see `=-10cm`
`:. (1)/(f)=(1)/(v)-(1)/(u)implies(1)/(f)=(1)/(-10)-(1)/((-60))impliesf=-12cm`