A convergent beam of ligh passes through a diverging lens of focal length 0.2 meters comes to focus at a distance 0.3 meters behind the lens find the position of the point at which the beam would converge in the absence of lens?

Explanation

F=-0.2m, v=0.3m
From the lens equation 1/f=1/v-1/u
1/u=1/v-1/f=1/0.3-1/-0.2=50/6
U=6/50=0.12m
In the absence of lens the beam would converge at a distance 0.12m from the present position of the lens.