Q. If tube length of astronomical telescope is $105\ cm$ and magnifying power is 20 for normal setting, calculate the focal length of objective
A) $100\ cm$
B) $10\ cm$
C) $20\ cm$
D) $25\ cm$
Explanation
(a) $|m| = \frac{f_{o}}{f_{e}} = 20\ $and $L = f_{o} + f_{e} = 105 \Rightarrow f_{o} = 100\ cm$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.