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A telescope is fitted with an objective lens of focal length 100 cm and an eyepiece of focal length 5 cm. If the final image is adjusted to form at the least distance of distinct vision, what is the telescope’s magnifying power?

1. 20
2. 24
3. 28
4. 32

Correct answer: 24

Solution

For final image at the least distance of distinct vision (D = 25 cm), M = (fo/fe)(1 + fe/D) = (100/5)(1 + 5/25) = 20 x 1.2 = 24.

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