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A highly polished surface which is smooth enough to reflect a good fraction of light incident on it is called a mirror. The mirror may be a highly polished metal surface or an ordinary glass plate coated with a thin silver layer.

The commonly used mirrors are of three types: plane mirror, spherical mirror or parabolic mirror, according as the reflecting surface is plane, spherical or parabolic.

 A highly polished and smooth curved surface is called a spherical mirror.When a piece of spherical glass is cut and one side is polished to make it a reflecting surface,it forms a spherical mirror.

Spherical mirrors are of two types:

When the reflection of light occurs from the hollow inner side of the curved mirror,it is called a concave mirror.

When the reflection takes place from outer bulging surface of a curved mirror,it is called convex mirror.