If the focal length of the lens is 20 cm, find the distance of the image from the lens in the following figure?

Explanation

According to figure, the point on the right side on the lens of which rays converge will behave as virtual object at the lens.
`therefore u=+12 cm,f=20 cm`
By lens formula,`1/f=1/v-1/u`
`therefore 1/20=1/v-1/12`
or `1/v=1/20+1/12=(3+5)/60=8/60`
or `v=60/8`=7.5 cm
so, image will be formed on same side of the virtual object at a distance of 7.5 cm from the lens.