Question

The rear –view mirror of a car is
a) plane
b) convex
c) concave
d) either convex or concave

Answer 1

Hint: The rear view mirrors in the cars should have a wider field of view i.e. the driver should be able to see more space on the road through the mirror. Secondly the image should be formed behind the mirror i.e. virtual and erect. So we can approach an answer from the given options if all these conditions are satisfied.

Complete step by step answer:
To begin with let us first see the properties of a concave mirror

If we place an object in front of a concave mirror beyond its focus then the mirror forms the real inverted and a magnified image of the object. Since it forms a magnified image the field of view gets reduced This is in contradiction to the criteria required to use a mirror as a rear view mirror. Hence concave mirrors cannot be used as a rear view mirror.
Now let us observe the above diagram of a convex mirror and a plane mirror and see whether they can be used as rear view mirrors.

Speaking about the plane mirror it forms a virtual erect and image of the same size as the object. Hence the field of view somewhat remains the same. But if we consider the convex mirror, it forms virtual, erect and the image of the object is not magnified. Hence the field of view gets increased.
 Since a convex mirror satisfies all the criteria of a rear view mirror.

So, the correct answer is “Option B”.

Note: The image in a concave mirror Is virtual and erect if the object is placed between the focus and the centre of the mirror. But a driver should be able to see even the traffic at a suitable distance at the back. In that case the focal length of the concave mirror required should have been very large which is practically not possible.