(a) The reflecting telescopes are preferred over refracting type because of the following reasons:
(i) There is no chromatic aberration in case of reflecting telescopes as the objective is a mirror.
(ii) Spherical aberration is reduced in case of reflecting telescopes by using mirror objective in the form of a paraboloid.
(b) For convex mirror, focal length is always positive, f = +ve An object is placed on the left side of the mirror. So, the object distance, u = −ve or u < 0. Using the mirror formula we have, 1f=1v+1u⇒1v=1f-1u Since f > 0 and u < 0, then from the above equations, we get that 1v>0⇒v<0 Hence, a virtual image is always formed at the back side of the mirror. Therefore, the image formed by the convex mirror is always virtual in nature, independent of the location of the object.