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  4. The magnifying power of a telescope with tube length 60 cm is 5. What is the focal length of its eye piece ?

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Q. The magnifying power of a telescope with tube length 60 cm is 5. What is the focal length of its eye piece ?

JEE MainJEE Main 2020Ray Optics and Optical Instruments

Solution:

$L=f_{0}+f_{e}-60\,cm$
$M=\frac{f_{0}}{f_{e}}=5$
$\Rightarrow f_{0}=5f_{e}$
$\therefore 6f_{e}=60\,cm$
$f_{e}=10\,cm$