Q. An astronomical telescope has objective and eye-piece lenses of powers 0.5 D and 20 D respectively. What will be its magnifying power?
A) 30
B) 10
C) 40
D) 20
Explanation
(c) Given , the power of objective lens,
$P_{0}\ = \ 0.5\ D$
The power of eye-piece lens,
$P_{e} = \ 20\ D$
The magnifying power of an astronomical telescope
$M = \frac{f_{0}}{f_{e}}$
$or\ M = \frac{P_{e}}{P_{0}}\ \ \ \ \ \ \ \ \ \ \ \ \left( \therefore P = \frac{1}{f} \right)$
$= \frac{20}{0.5} = 40$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.