Four lenses of focal length $\pm 15 \mathrm{~cm}$ and $\pm 150 \mathrm{~cm}$ are available for makin

Question

Four lenses of focal length $\pm 15 \mathrm{~cm}$ and $\pm 150 \mathrm{~cm}$ are available for making a telescope. To produce the largest magnification, the focal length of the eyepiece should be\

Professor PC Thomas Classes · Answer

(a) : Magnifying power of telescope,\ $M=f_{o} / f_{e}$\ To produce largest magnifications $f_{o}>f_{e}$ and $f_{o}$ and $f_{e}$ both should be positive (convex lens).\ Therefore $f_{e}=+15 \mathrm{~cm}$.