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 the end closer to the pole is 20 cm away from it. Find the length of the image.

Explanation

Since point `A` is centre of curvature image of `A` is formed on A itself.
Image of B: `u=-30cm,f=-10cm,v=?`
`(1)/(v)+(1)/(u)=(1)/(f)implies(1)/(v)+(1)/(-30)=(1)/(-10)`
`(1)/(v)=-(1)/(10)+(1)/(30)=(-3+1)/(30)`
`v=-15cm`
Length of image
`A^(')B^(')=20-15=cm`