A convex lens of focal length `20 cm` and a convex mirror of focal length `10 cm` are placed co-axially `50 cm` apart from each other. An incident beam parallel to its principal axis is incideent on the convex lens. Locate the position of final image formed due to the combination.

Explanation

The parallel beam of light falling on convex lens will form an image at focus of convex lens, i.e., at 20 cm. This image at O will act as an object for concave mirror.
Thus for concave mirror `u=-30cm`
`f=-10cm`
`(1)/(v)=(1)/(f)-(1)/(u)`
`=-(1)/(10)-((-1)/(30))`
`v=-15cm.`
The real image will be formed at a distance of 15 cm from concave mirror.