Question

A convex lens of focal length $15cm$ is placed on a plane mirror. An object is placed at $30cm$ from the lens. The image is

• A. real, at $30cm$ in front of the mirror
• B. real, at $30cm$ behind the mirror
• C. real, at $10cm$ in front of the mirror
• D. virtual, at $10cm$ behind the mirror

Answer 1

Answer: (C)

$\frac{1}{F}=\frac{1}{f_l}+\frac{1}{f_m}+\frac{1}{f_l}=\frac{2}{f_l}+\frac{1}{\infty }$
$\Rightarrow F=\frac{15}{2}cm$
$\frac{2}{15}=\frac{1}{30}+\frac{1}{v},v=10cm$.
$\therefore$ image is real, $10cm$ in front of mirror.