A thin rod of length `d//3` is placed along the principal axis of a concave mirror of focal length = d such that its image, which is real and elongated, just touches the rod. Find the length of the image ?

Options

A. f
B. `1/2f`
C. 2f
D. `1/4f`

Answer

B

Explanation

(b) For end A of the rod,
`u=2f-f/3=(5f)/3`

By using,`1/f=1/v+1/u rArr1/(-f)=1/v+1/(-5f//3)`
`therefore v=-5/2f`
So, thelength of image=`5/2f-2f=f/2`