Question

A Plane mirror is placed on the other side of a cover lens having a focal length of 12 cm. A distinct image is formed in front of the lens (towards the object) when the plane mirror is at a distance of 45 cm from the lens, Calculate the distance of image from the lens. 

Answer 1

$$\frac{1}{F}=\frac{1}{f}+\frac{1}{f_m}+\frac{1}{f}\\\frac{1}{F}=\frac{1}{15}+\frac{1}{\infty}+\frac{1}{15}\\F=7.5\ cm$$

$$\frac{1}{7.5}=\frac{1}{30}+\frac{1}{d}\\d=10\ cm$$