Optics Question 348
Question: The magnifying power of a microscope with an objective of 5 mm focal length is 400. The length of its tube is 20 cm. Then the focal length of the eye-piece is
[MP PMT 1991]
Options:
A) 200 cm
B) 160 cm
C) 2.5 cm
D) 0.1 cm
Show Answer
Answer:
Correct Answer: C
Solution:
If nothing is said then it is considered that final image is formed at infinite and $ {m _{\infty }}=\frac{({L _{\infty }}-f _{o}-f _{e})\ .D}{f _{o}f _{e}}\underline{\tilde{\ }}\frac{LD}{f _{0}f _{e}} $
$ \Rightarrow 400=\frac{20\times 25}{0.5\times f _{e}}\Rightarrow f _{e}=2.5\ cm. $
