Q. A telescope consists of two thin lenses of focal lengths 0.3 m and 3 cm respectively. It is focused on moon which subtends on angle of $0.5{^\circ}$ at the objective. Then, the angle subtended at the eye by the final image will be
A) $5{^\circ}$
B) $0.25{^\circ}$
C) $0.5{^\circ}$
D) $0.35{^\circ}$
Explanation
(a) For a telescope
$\frac{\beta}{\alpha} = \frac{f_{0}}{f_{e}}$
$\therefore\frac{\beta}{0.5{^\circ}} = \frac{0.3}{0.03} \Longrightarrow \beta = 5{^\circ}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.