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
Cutting a symmetric biconvex lens into two plano-convex halves leaves each half with one curved surface, so its power is halved and its focal length doubles: $f_o' = 2f_o$.
The magnification of a compound microscope is $m \approx \dfrac{L}{f_o}\cdot\dfrac{D}{f_e}$. To keep $m$ the same with $f_o$ doubled, the tube length $L$ must be doubled.
Solution by Sreeraj P, M.Sc Physics