Q 12-09-099JEE MainJEE Main 2024 (30 Jan, Shift 1)Easy
The distance between an object and its two times magnified real image as produced by a convex lens is $45\ \text{cm}$. The focal length of the lens used is ______ cm.
Numerical value type. Enter your answer.
Answer: 10
Real image, $m = -2$: $v = 2u$ (in magnitude) and $u + v = 45$, so $u = 15\ \text{cm}$, $v = 30\ \text{cm}$.
$$\frac1f = \frac1{30} + \frac1{15} = \frac3{30} \Rightarrow f = 10\ \text{cm}$$
Solution by Sreeraj P, M.Sc Physics