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CBSE Class 12 Physics 2017 Delhi Set 2 Paper

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Question : 3 of 8
Marks: +1, -0
Why should the objective of a telescope have large focal length and large aperture? Justify your answer.
Solution:  
Reasons for having large focal length and large aperture of objective of telescope and their justification.
Large focal length : to increase magnifying power
(∵m=  f0fe)\left(\because m=\;\frac{f_0}{f_e}\right)
Large aperture : to increase resolving power. 12\frac{1}{2}
(∵RP=  2a1.22λ)\left(\because RP=\;\frac{2 a}{1.22 \lambda}\right)
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