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The focal length of objective lens of an astronomical telescope is 1 m. If magnifying power of telescope is 20, then what is length of telescope for relaxed eye?
  • a)
    85 cm
  • b)
    95 cm
  • c)
    105 cm
  • d)
    115 cm
Correct answer is option 'C'. Can you explain this answer?
Verified Answer
The focal length of objective lens of an astronomical telescope is 1 m...
For relaxed eye → m = fo/fe
or 20 = 100/fe 
or fe = 5 cm
The length of the telescope for relaxed eye is
L = fo + ue = 100 + 5 = 105 cm
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Most Upvoted Answer
The focal length of objective lens of an astronomical telescope is 1 m...
Given:
Focal length of objective lens, f = 1 m
Magnifying power of telescope, M = 20

To find: Length of telescope for relaxed eye

Formula used:
Magnifying power of telescope, M = (focal length of objective lens / focal length of eyepiece) + 1

Calculation:
Let the focal length of eyepiece be e.
Given, M = 20
f = 1 m

Using the formula,
M = (f/e) + 1

20 = (1/e) + 1

19 = 1/e

e = 1/19 m

Total length of telescope, L = f + e
L = 1 + (1/19)
L = 20/19 m

Converting to cm,
L = (20/19) × 100 cm
L = 105.26 cm ≈ 105 cm

Therefore, the length of the telescope for a relaxed eye is 105 cm, which is option (c).
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Community Answer
The focal length of objective lens of an astronomical telescope is 1 m...
105 cm
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The focal length of objective lens of an astronomical telescope is 1 m. If magnifying power of telescope is 20, then what is length of telescope for relaxed eye?a)85 cmb)95 cmc)105 cmd)115 cmCorrect answer is option 'C'. Can you explain this answer?
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