Question
Why do we prefer a convex mirror as a rear-view mirror in vehicles?
Solution
Convex mirrors are used as rear-view mirror in vehicles because of the following two reasons:
1. A convex mirror always forms an erect, virtual and diminished image of an object placed anywhere in front of it.
2. A convex mirror has a wider field of view than a plane mirror of the same size. Thus, convex mirrors enable the driver to view much larger traffic behind him than would be possible with a plane mirror.
The disadvantage of a convex mirror is that it does not give the correct distance and hence, the speed of the vehicle approaching from behind cannot be estimated precisely. 
The Fig. above shows the field of view of (a) a plane mirror (b) a convex mirror.
