Q. A concave lens of focal length 20 cm product an image half in size of the real object. The distance of the real object is
A) 20 cm
B) 30cm
C) 10cm
D) 60cm
Explanation
(a) $m = \frac{f}{f + u}$
$\frac{1}{2} = \frac{- 20}{- 20 + u}\ or - 20 + u = - 40$
Or $\ u = - 40 + 20\ $or$\ \ u = - 20\ cm$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.