Optics Question 415
Question: The focal lengths of the lenses of an astronomical telescope are 50 cm and 5 cm. The length of the telescope when the image is formed at the least distance of distinct vision is
[EAMCET (Engg.) 2000]
Options:
A) $ 45cm $
B) $ 55cm $
C) $ \frac{275}{6}cm $
D) $ \frac{325}{6}cm $
Show Answer
Answer:
Correct Answer: D
Solution:
Length of the telescope when final image is formed at least distance of distinct vision is $ L=f _{o}+u _{e}=f _{o}+\frac{f _{e}D}{f _{e}+D} $
$ =50+\frac{5\times 25}{5+25}=\frac{325}{6}cm $
