Question

A concave mirror cannot be used as a:
A. Torch reflector
B. Dentist’s mirror
C. Rearview mirror
D. Magnifying mirror

Answer 1

There are many types of the mirror according to their shapes. Some of the types are the concave, convex, plane, etc. When light rays strike at a mirror, different types of images are formed due to their shapes. The properties and the usage of the mirror change according to their type. Mirrors are used for reflecting the light rays and depending on the position of the object, an image is formed.

Complete step by step solution:
Mirrors having curved surfaces are called spherical mirrors. A spherical mirror is a segment of a big spherical surface and has circular edges. Concave and convex mirrors are two different types of spherical mirrors. When the light gets reflected from the inner curved surface of the mirror, then the mirror is called a concave mirror. Similarly, if the light gets reflected from the outer bulging part of the mirror then it is called a convex mirror.
When parallel rays of light are incident on the concave mirror, they get reflected and converge at a point. Such a point is known as the focal point or principal focus. When parallel beams of light are incident on the convex mirror, they get reflected and appear to diverge from a point behind the mirror. This point is the principal focus or focal point of the convex mirror.
Wherever the object may be, the image formed by the concave mirrors is real and inverted except when the object lies between focus and the pole. In this case, the image formed is virtual and erect and lies behind the mirror. But the size of the image depends on the position of the object. In the case of a convex mirror, the image formed is virtual, erect, and diminished and is in between focus and pole irrespective of the position of the object.
According to the question, a torch reflector uses a concave mirror as the light source is placed at the focus of the mirror and after reflection, we get parallel beams of light having high intensity and larger coverage. The dentist’s mirror and magnifying mirror also use a concave mirror as the image formed by it is enlarged therefore getting a better view.
But in the case of a rearview mirror, a concave mirror cannot be used as the object is far away. Thus the image formed by it is real, enlarged, and inverted. Thus a small mirror would not be able to cover the maximum area. As the image is inverted, the driver would not be able to get the position of the vehicle behind him. A convex mirror is used in this case.
Therefore, option (C) is the correct answer.

Note: Telescopes and microscopes use a concave mirror as it helps to concentrate a parallel beam of light coming from astronomical bodies to a point or the specimen. To eliminate the blind spots in a building, a convex mirror is used in hallways to get a wider view of the space. Plane mirrors are different from spherical mirrors. The image formed by a plane mirror is virtual and erect and of the same size as the object i.e. its magnification is unity. Also, the image is laterally inverted.