__Answer :__

__(i)-(b) Convex__

The lenses and must be convex. The focal length of the lens is large with a large aperture in order to accommodate maximum light rays coming from the outer-space with a minimum drop in its intensity.

The lens, , is of smaller focal length. It produces an enlarged but sharp virtual image of the distant object i.e. m (magnification is inversely correlated to the focal length; in other words, smaller the focal length, greater will be the size of the image thus obtained)

(ii)-(b) 1:4

Power of a spherical lens is given as

The power of each lens is;

and

It is given, that the ratio of the power of and is 4:1. The focal length of the lenses can be written as

Hence f_{1}/f_{2}=1/4

(iii)-(a) Ratio of the height of the image to the height of the object

The linear magnification of a spherical lens is given as

(iv)-(c) 8 cm

The lateral magnification of a spherical lens is given as

Hence, u = 8 cm

(v)-(c) Not-so-thick lenses would not make the telescope very heavy and they will also allow a considerable amount of light to pass through them.

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