Converging rays are incident ono a convex spherical mirror so that their extensions intersect 30cm behind the mirror on the optical axis. The reflected rays form a diverging beam so that their extensions intersect the optical axis 1.2 m from the mirror. Determine the focal length of the mirror.

Explanation

In this case: `u=+30` and `v=+120`
`:. (1)/(f)=(1)/(v)+(1)/(u)=(1)/(120)+(1)/(30)`
`rArr f=24cm`