Q. A convex lens of focal length $f\ $produces a virtual image $n$ times the size of the object. Then the distance of the object from the lens is
A) $(n - 1)f$
B) $(n + 1)f$
C) $\left( \frac{n - 1}{n} \right)f$
D) $\left( \frac{n + 1}{n} \right)f$
Explanation
(c) $n = \frac{f}{f + u}$
$f + u = \frac{f}{n}$
Or $\ u = \frac{f}{n} - f = \left( \frac{1 - n}{n} \right)f$
Or $u = - \left( \frac{n - 1}{n} \right)f,|u| = \frac{n - 1}{n}f$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.