Q. A spherical mirror forms diminished virtual image of magnification 1/3. Focal length is 18 cm. The distance of the object is
A) 18 cm
B) 36 cm
C) 48 cm
D) Infinite
Explanation
(b) Clearly, the given mirror is a convex mirror
$m = \frac{f}{f - u}$
$\frac{1}{3} = \frac{18}{18 - u}$
Or $\ 3 \times 18 = 18 - u$
Or $u = - 2 \times 18\ cm\ $or$\ u = - 36\ cm$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.