Q. A man has a concave shaving mirror of focal length 0.2 m. How far should the mirror be held from his face in order to give an image of two fold magnification?
A) 0.1 m
B) 0.2 m
C) 0.3 m
D) 0.4 m
Explanation
(a) $m = \frac{f}{f - u}$
$2 = \frac{- 0.2}{- 0.2 - u}$
Or $2 = \frac{0.2}{0.2 + u}\ $or$\ \ 0.4 + 2u = 0.2$
Or $2u = 0.2 - 0.4 = - 0.2$
Or $\ u = - 0.1\ m$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.