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 $



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