Q 12-09-148JEE MainJEE Main 2022 (27 Jun, Shift 2)Medium
A convex lens has power $P$. It is cut into two halves along its principal axis. Further one piece (out of the two halves) is cut into two halves perpendicular to the principal axis (as shown in figures). Choose the incorrect option for the reported pieces.
Answer: (A) Power of $L_1 = \dfrac P2$
Cutting along the principal axis does not change the curvatures, so $L_1$ keeps power $P$.
Cutting perpendicular to the axis splits the half into two plano-convex pieces. By the lens maker's formula each has one curved surface instead of two, so each has power $\dfrac P2$.
So $L_2 = L_3 = \dfrac P2$ and $L_1 = P$. The incorrect option is "Power of $L_1 = \dfrac P2$".
Solution by Sreeraj P, M.Sc Physics