Optics Question 394
Question: The magnifying power of an astronomical telescope is 8 and the distance between the two lenses is 54 cm. The focal length of eye lens and objective lens will be respectively
[MP PMT 1991; CPMT 1991; Pb. PMT 2001]
Options:
A) 6 cm and 48 cm
B) 48 cm and 6 cm
C) 8 cm and 64 cm
D) 64 cm and 8 cm
Show Answer
Answer:
Correct Answer: A
Solution:
$ f _{o}+f _{e}=54 $ and $ \frac{f _{o}}{f _{e}}=m=8\Rightarrow f _{o}=8f _{e} $
$ \Rightarrow 8f _{e}+f _{e}=54\Rightarrow f _{e}=\frac{54}{9}=6 $
$ \Rightarrow f _{o}=8f _{e}=8\times 6=48 $
