Q 12-09-044JEE MainJEE Main 2026 (5 Apr, Shift 1)Medium
A compound microscope is designed with two symmetric biconvex lenses. The objective lens is cut vertically, creating two identical plano-convex lenses. One of them is used in place of original objective lens. To retain same magnification keeping the object distance unchanged, the tube length has to be
Answer: (A) increased two times
Concept. Cutting a symmetric biconvex lens perpendicular to its axis gives two plano-convex lenses, each of focal length $2f_o$. The objective's magnification is $m_o\approx\dfrac{L}{f_o}$.
Step 1. New objective. $f_o'=2f_o$.
Step 2. Same magnification. $\dfrac{L'}{2f_o}=\dfrac{L}{f_o}$, so $L'=2L$.
Answer. Increased two times (Option A).
Solution by Sreeraj P, M.Sc Physics
