A short linear object of length L lies on the axis of a spherical mirror of focal length f at a distance 'u' from the mirror. Its image has an axial length 'l' equal to

Question

$\begin{array}{1 1} L \bigg[ \large\frac{f}{u-f}\bigg]^{1/2} \\ L \bigg[ \large\frac{u+f}{f}\bigg]^{1/2} \\ L \bigg[ \large\frac{u-f}{f}\bigg]^{1/2} \\ L \bigg[ \large\frac{f}{u-f}\bigg]^{2} \end{array}$