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Solution


Q.

A lens of large focal length and large aperture is best suited as an objective of an astronomical telescope since           [2021]
1 a large aperture contributes to the quality and visibility of the images.  
2 a large area of the objective ensures better light gathering power.  
3 a large aperture provides a better resolution.  
4 all of the above.     

Ans.

(4)

As the focal length is large, so it enhances the magnifying power of telescope. The large aperture or diameter of lens helps in collecting large amount of light from the object so that the image formed is bright.

The resolving power of telescope is

            R.P.=D1.22λ

where, D is diameter or aperture of lens and λ is wavelength of light used.

So, all options are correct.