For the pencil kept along the principal axis and the end of the pencil closest to pole is at 20 cm,
say, u1 = -20 cm
Flence, the other end of the stick is at distance, u2 = (u1 + 20) = -40 cm from pole of the mirror.
As R = -30 cm, F = \(\frac{R}{2}\) = -15 cm
Using mirror formula for concave mirror,
Also, for other end of the stick,
∴ v2 = -24 cm
Here, negative signs indicate that images are formed on the left of the mirror.
The length of the image formed is given by,
v = v2 – v1 = -24 – (-60) = 36 cm.