Question:
For an astronomical telescope of length 126 cm in normal adjustment, if the focal length of the objective is 850 % more than that of its eyepiece, then the focal length of the eyepiece is:
For an astronomical telescope of length 126 cm in normal adjustment, if the focal length of the objective is 850 % more than that of its eyepiece, then the focal length of the eyepiece is:
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Normal adjustment: $L = f_o + f_e$.
Updated On: Jun 6, 2026
- 12 cm
- 114 cm
- 18 cm
- 108 cm
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The Correct Option is A
Solution and Explanation
Step 1: Concept
Telescope length $L = f_o + f_e$.
Step 2: Meaning
$f_o$ is 850
Step 3: Analysis
$L = 9.5 f_e + f_e = 10.5 f_e$. $126 = 10.5 f_e \rightarrow f_e = 126 / 10.5 = 12$ cm.
Step 4: Conclusion
The focal length of the eyepiece is 12 cm.
Final Answer: (A)
Telescope length $L = f_o + f_e$.
Step 2: Meaning
$f_o$ is 850
Step 3: Analysis
$L = 9.5 f_e + f_e = 10.5 f_e$. $126 = 10.5 f_e \rightarrow f_e = 126 / 10.5 = 12$ cm.
Step 4: Conclusion
The focal length of the eyepiece is 12 cm.
Final Answer: (A)
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