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. The length of the image is

$\text{f}=-10\text{cm}$

$\text{R}=\text{2f}=-\text{20}\text{cm}$

Length of AB = 10 cm

Distance of end A = 20 cm

Distance of end ${\text{B}}^{|}=10+20=30\text{cm}$

$\text{u}=-\text{30}\text{cm}$

$\frac{\text{1}}{\text{f}}=\frac{\text{1}}{\text{u}}+\frac{\text{1}}{\text{v}}$

$\frac{\text{1}}{\text{v}}=\frac{1}{-10}+\frac{1}{30}$

$\text{v}=-\frac{20}{300}$

$\text{v}=-\frac{1}{15}$

$\text{v}=-15\text{cm}$

Length of ${\text{A}}^{|}{\text{B}}^{|}=20-15=5\text{cm}$