A lens of focal length 12 cm produces a virtual image,whose linear dimensions are `1//3` that of the object.What kind of a lens is it?Dtermine the position of the object and the image.

Explanation

As the image formed by lens is virtual and smaller than size of object.
`:.` Given lens is a concave lens
`m=1/3`
`f=-12cm`
Magnification `m=v/u`
`v/u=1/3`
`v=3u`
We know `1/v-1/u=1/f`
`1/(3u)-1/u=-1/12`
`(1-3)/(3u)=-1/12`
`(-2)/(3u)=-1/12`
`u=24/3=8cm`
`impliesu=3u=3(8)=24cm`