Optics Question 381
Question: The focal length of objective and eye lens of a astronomical telescope are respectively 2 m and 5 cm. Final image is formed at (i) least distance of distinct vision (ii) infinity. The magnifying power in both cases will be
[MP PMT/PET 1988]
Options:
A) - 48,- 40
B) - 40,- 48
C) - 40, 48
D) - 48, 40
Show Answer
Answer:
Correct Answer: A
Solution:
When the final image is at the least distance of distinct vision, then $ m=-\frac{f _{o}}{f _{e}}( 1+\frac{f _{e}}{D} )=\frac{200}{5}( 1+\frac{5}{25} )=\frac{200\times 6}{5\times 5}=-\ 48 $ When the final image is at infinity, then $ m=\frac{-f _{o}}{f _{e}}=\frac{200}{5}=-\ 40 $
