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Question: Answered & Verified by Expert
If tube length of astronomical telescope is $105 \mathrm{~cm}$ and magnifying power is 20 for normal setting, calculate the focal length of objective
PhysicsRay OpticsJEE Main
Options:
  • A $100 \mathrm{~cm}$
  • B $10 \mathrm{~cm}$
  • C $20 \mathrm{~cm}$
  • D $25 \mathrm{~cm}$
Solution:
2869 Upvotes Verified Answer
The correct answer is: $100 \mathrm{~cm}$
$|m|=\frac{f_o}{f_e}=20$ and $L=f_o+f_e=105 \Rightarrow f_o=100 \mathrm{~cm}$

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