Q 12-09-098JEE MainJEE Main 2024 (9 Apr, Shift 2)Easy
The following figure represents two biconvex lenses $L_1$ and $L_2$ having focal lengths $10\ \text{cm}$ and $15\ \text{cm}$ respectively. The distance between $L_1$ and $L_2$ is:
Answer: (C) $25\ \text{cm}$
A ray parallel to the axis passes through the second focus of $L_1$. It emerges parallel from $L_2$, so the same point must be the first focus of $L_2$. The foci coincide:
$$d = f_1 + f_2 = 10 + 15 = 25\ \text{cm}$$
Solution by Sreeraj P, M.Sc Physics