The focal lengths of the lens of an astronomical telescope are 50cm and 5cm. The length of the telescope when the image is formed at the least distance of distance vision is ( in cm )
A
2506
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B
2756
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C
3256
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D
3506
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Solution
The correct option is C3256 focal length of objective fo=50cm
focal length of eye piece fe=5cm
Length of telescope is L=f0+|ue|
for least distance of distinct vision D=|ve|=25cm
Lens formula at eye piece 1fe=1ve−1ue 15=−125−1ue 1ue=−[125+15]=−625 ue=−256cm ∴L=f0+ue=50+256=3256cm