Q. An opera glass (Gallilean telescope) measures $9\ cm$ from the objective to the eyepiece. The focal length of the objective is $15\ cm$. Its magnifying power is
A) $2.5$
B) $2/5$
C) $5/3$
D) $0.4$
Explanation
(a) $f_{o} - f_{e} = 9\ cm$ and $f_{e} = f_{o} - 9 = 15 - 9 = 6\ cm$
$\Rightarrow m = \frac{f_{o}}{f_{e}} = \frac{15}{6} = 2.5$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.