Q. A concave mirror of focal length $15\ cm$ forms an image having twice the linear dimensions of the object. The position of the object when the image is virtual will be
A) 22.5 $cm$
B) 7.5 $cm$
C) 30 $cm$
D) 45 $cm$
Explanation
(b) $f = - 15cm,\ m = + 2$ [Positive because image is virtual]
$\because m = - \frac{v}{u} \Rightarrow v - 2u$. By using mirror formula
$\frac{1}{- 15} = \frac{1}{( - 2u)} + \frac{1}{u} \Rightarrow u = - 7.5\ cm$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.