Q. A telescope has an objective lens of focal length $200\ cm$ and an eye piece with focal length $2\ cm$. If this telescope is used to see a 50 $meter$ tall building at a distance of $2\ km$, what is the height of the image of the building formed by the objective lens
A) $5\ cm$
B) $10\ cm$
C) $1\ cm$
D) $2\ cm$
Explanation
(a) Magnification of objective lens $m = \frac{I}{O} = \frac{v_{0}}{u_{0}} = \frac{f_{0}}{u_{0}}$
$\Rightarrow \frac{I}{50} = \frac{200 \times 10^{- 2}}{2 \times 10^{3}} \Rightarrow I = 5 \times 10^{- 2}m = 5\ cm$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.