Physics - Geometrical Optics Question with Solution | TestHub

A source of light is a thin thread of length $\ell =10\mathrm{cm}$ located on the principal axis of a converging lens with focal length $\mathrm{f}=5\mathrm{cm}$ and diameter $\mathrm{D}=1\mathrm{cm}$. The near end of the thread is located a distance $\mathrm{a}=10\mathrm{cm}$ from the lens. Find the minimum size (diameter in mm) of the illuminated spot on a screen placed on the other side of the lens perpendicular to the lens principal axis.