Physics Question from JEE Main 2026 · 21 January, Shift 1

A collimated beam of light of diameter $2 \, \text{mm}$ is propagating along the $x$-axis. The beam is required to be expanded into a collimated beam of diameter $14 \, \text{mm}$ using a system of two convex lenses. If the first lens has focal length $40 \, \text{mm}$, then the focal length of the second lens is _____ $\text{mm}$.