Q. The focal length of the objective and eye-piece of a telescope are respectively $100\ cm$ and $2\ cm$. The moon subtends an angle of $0.5{^\circ}$ at the eye. If it is looked through the telescope, the angle subtended by the moon’s image will be
A) $100{^\circ}$
B) 50${^\circ}$
C) 25${^\circ}$
D) 10${^\circ}$
Explanation
(c) $\frac{\beta}{\alpha} = \frac{f_{o}}{f_{e}} \Rightarrow \frac{\beta}{0.5{^\circ}} = \frac{100}{2} \Rightarrow \beta = 25{^\circ}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.