Optics Question 387
Question: An astronomical telescope has an angular magnification of magnitude 5 for distant objects. The separation between the objective and the eye piece is 36 cm and the final image is formed at infinity. The focal length fo of the objective and the focal length fe of the eye piece are
[IIT 1989; MP PET 1995; JIPMER 2000]
Options:
A) fo = 45 cm and fe = - 9 cm
B) fo = 7.2 cm and fe = 5 cm
C) fo = 50 cm and fe = 10 cm
D) fo = 30 cm and fe = 6 cm
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Answer:
Correct Answer: D
Solution:
In this case $ |m|\ =\frac{f _{o}}{f _{e}}=5 $ …. (i)
and length of telescope $ =f _{o}+f _{e}=36 $ …. (ii)
Solving (i) and (ii), we get fe = 6 cm, $ f _{o}=30cm. $
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