Mirrors are the basic means of viewing our own beauty. Generally mirrors refer to plane mirrors. But if the surface of a mirror is curved we call it a spherical mirror. The mirror that is coated outside and reflecting inside is the concave mirror. Whereas the mirror that is reflecting outside is the convex mirror. Even spherical mirrors follow the laws of reflection.
The geometric centre of a spherical mirror is called its pole. The centre of the hollow sphere for which the mirror is a part, is called the centre of curvature. The line joining the centre of curvature and the pole is the principal axis. A light ray incident on a spherical mirror, after reflection appears to pass through the principal focus in the case of a convex mirror and passes through the focus in the case of concave mirror. The diameter of the spherical mirror gives the measure of its aperture.
Convex mirrors diverge the light incident on it. Hence, called the diverging mirrors. Due to this they always form diminished, virtual and erect images irrespective of the position of the object in front of them. Thus, the magnification produced by these mirrors is always less than one.
Concave mirrors converge the light and hence are called the converging mirrors. You can observe yourself magnified when the mirror is placed close to your face. This is due the position of the object between the focus and the pole. As the object moves away from the mirror, the size of its image reduces along with its distance from the mirror.
The distance from the principal focus to the pole of the mirror is the focal length of the mirror and is equal to half the radius of curvature, which is the distance between the centre of curvature and the pole.
The relation between the focal length (f), object distance (u) and the image distance (v) is given by 1/f = 1/v + 1/u
All the distances are measured from the pole of the mirror. If we measure the distances in the direction of the incident light, then they are taken positive and else they are taken negative. These constitute the sign conventions.
Rear view mirrors of vehicles and the ones used in ATM centres are convex.
Mirrors used by dentists to view a magnified view of the interior parts of the mouth are concave.