An astronomical telescope consists of an objective of focal length 50 cm and eyepiece of focal length 2 cm is focused on the moon so that the final image is formed at the least distance of distinct vision (25 cm). Assuming angular diameter of moon as (1/2)° at the objective, the angular size of image is:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 13.5°
The angular magnification, M is,
$M=\frac{-f_o}{f_e}=\frac{-50}{2}=-25$
⇒ Angular size, $θ_i=M×θ_o$
$=-25×\frac{1}{2}=12.5°$