. (A) : Optical instruments are assembled using
lenses with very wide apertures
(R) : Wide aperture of lenses enables them
to collect more light and produce bright
images.

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Both 'A' and 'R' are true and 'R' is the correct explanation of 'A'.

Both 'A' and 'R' are true and 'R' is not the correct explanation of 'A

'A' is true and 'R' is false

Both 'A' and ‘R’ are false

answer is A.

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Detailed Solution

A lens of large aperture and at the same time free from lens aberrations cannot be manufactured. Therefore the lens used in the telescope cannot be of the very large aperture. Thus, light gathering power of such a telescope will be very low and hence it will not enable us to see faint stars. The spherical aberrations can be eliminated by making use of the parabolic mirror in case of a large mirror. Since mirror of large apertures can be easily designed, reflecting type telescope will have large light gathering power. Because of these reasons reflected type of telescopes are preferred.

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