There are two types of curved spherical mirrors, concave and convex. These mirrors are made by depositing vaporized aluminium on a glass surface which would form a part of a sphere. Deposition on the outside of the glass makes a concave (or converging) mirror, while deposition on the inside makes a convex (or diverging) mirror. When the sun's rays fall on a concave mirror, these are reflected so as to converge to a point called the focus of mirror. Since a concave mirror can concentrate the sun's radiation falling on it at one point, it can be used as a burning glass. It is because of this property that concave mirrors are used in solar cookers. Large concave mirrors are also used in reflecting telescopes for observing and photographing distant stars and other heavenly bodies. A concave mirror forms a virtual or real image depending on the position of the object. When an object is placed close to the mirror, i.e. At a distance less than the focal length of the mirror the image formed is virtual, erect and larger than the object. A concave mirror is thus used as a shaving or make-up mirror. Small concave mirrors are used by dentists for examining teeth. A convex mirror always produces virtual images. These images are erect and smaller than the objects.
