A converging beam of rays in incident on a diverging lens. Having passed through the lens the rays intersect at a point `15 cm` from the lens. If the lens is removed, the point where the rays meet, move `5 cm` closer to the mounting that holds the lens. Find the focal length of the lens.

Answer

C

Explanation

Using `1/f=1/v-1/u,`
or `1/f=1/(+15)-1/(+10)`
Solving, we get `f=-30 cm`