Q 12-09-010NEETNEET 2023Top questionEasy
Two thin lenses are of same focal lengths ($f$), but one is convex and the other one is concave. When they are placed in contact with each other, the equivalent focal length of the combination will be :
Answer: (D) Infinite
$$\frac{1}{F} = \frac{1}{f} + \frac{1}{-f} = 0 \;\Rightarrow\; F = \infty$$
The combination behaves like a plane glass plate.
Solution by Sreeraj P, M.Sc Physics