A person wants a real image of his own, 3 times enlarged. Where should he stand in front of a concave mirror of radius of curvature of 30cm.

Options

A. 90 cm
B. 10 cm
C. 20 cm
D. 30 cm

Answer

C

Explanation

Given, `m=-3` and R = 30 cm
`f=-(R )/(2)=-15 cm`
We know that, `m=-(v)/(u) rArr -3 =(-v)/(u)`
`v=3 u`
Also, `(1)/(f)=(1)/(v)+(1)/(u)`
`(1)/(-15)=(1)/(3u)+(1)/(u)rArr (-1)/(15)=(1+3)/(3u)`
`-3u=4xx15`
`rArr " " u=(-4xx15)/(3)`
Initial positive of a person, `u = -20 cm`