A rod of length 10 cm lies along the principal axis of a concave mirror of focal length 10 cm in such a way that its end closer to the pole is 20 cm away from the mirror. The length of the image is,

Explanation

The situation is shown in ure. The radius of curvature of the mirror is `r=2f=20cm.` Thus, the nearer end B of the rod AB is at the centre of the curvature and hence, its image will be formed at B itself.
we shall now locate the image of A.
Here u=-30 cm and f=-10 cm,. We have
`1/u+1/v=1/f`
or 1/v=1/f-1/u`
`= 1/(-10cm)-1/(-30cm)`
`=or v=-15cm`
Thus the image of A is formed at 15 cm from the pole. The length of the image is therefore 5.0 cm