Question
(a) Give two reasons to explain why reflecting telescopes are preferred over refracting type.
(b) Use mirror equation to show that convex mirror always produces a virtual image independent of the location of the object.Solution
a) Reflecting telescopes are preferred over refracting because of the following reasons:
i) There is no chromatic aberration as the objective is a mirror
ii) Spherical aberration is reduced in case of reflecting telescope by using mirror objective.
b) Focal length is always positive for convex mirror.
Consider an object placed on the left side of the mirror. That is u < 0.
Now, using the mirror formula,
Focal length is positive and object distance is negative.
Therefore, 
Hence, a virtual image is always formed at the back side of a mirror. That is, image formed by a convex mirror is virtual in nature.
