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Two lenses of focal lengths 5 cm and 50 cm are to be used for making a telescope. Which lens will you use for the objective?

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in Physics – Class 12 by (135k points)
Two lenses of focal lengths 5 cm and 50 cm are to be used for making a telescope. Which lens will you use for the objective?

(a) Both

(b) Neither

(c) 5 cm

(d) 50 cm

The question was posed to me in final exam.

Origin of the question is Optical Instruments in section Ray Optics and Optical Instruments of Physics – Class 12

1 Answer

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Best answer
The correct choice is (d) 50 cm

Easiest explanation: In a telescope, the objective should have a large focal length than the eyepiece. So the lens of 50 cm focal length will be used as the objective. So, the smaller one of the two, i.e. the 5 cm focal length lens will be used as the eyepiece.

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