Topics: Mirror, Glass, Light Pages: 6 (1965 words) Published: May 31, 2013
A mirror is an object that reflects light in a way that preserves much of its original quality subsequent to its contact with the mirror. Some mirrors also filter out some wavelengths, while preserving other wavelengths in the reflection. This is different from other light-reflecting objects that do not preserve much of the original wave signal other than color and diffuse reflected light. The most familiar type of mirror is the plane mirror, which has a flat surface. Curved mirrors are also used, to produce magnified or diminished images or focus light or simply distort the reflected image. Mirrors are commonly used for personal grooming or admiring oneself (in which case the archaic term looking-glass is sometimes still used), decoration, and architecture. Mirrors are also used in scientific apparatus such as telescopes and lasers, cameras, and industrial machinery. Most mirrors are designed for visible light; however, mirrors designed for other types of waves or other wavelengths ofelectromagnetic radiation are also used, especially in non-optical instruments. From Encyclopedia Britanica:

The typical mirror is a sheet of glass that is coated on its back with aluminum or silver that produces images by reflection. The mirrors used in Greco-Roman antiquity and throughout the European Middle Ages were simply slightly convex disks of metal, either bronze, tin, or silver, that reflected light off their highly polished surfaces. A method of backing a plate of flat glass with a thin sheet of reflecting metal came into widespread production in Venice during the 16th century; an amalgam of tin and mercury was the metal used. The chemical process of coating a glass surface with metallic silver was discovered by Justus von Liebig in 1835, and this advance inaugurated the modern techniques of mirror making. Present-day mirrors are made by sputtering a thin layer of molten aluminum or silver onto the back of a plate of glass in a vacuum. In mirrors used in telescopes and other optical instruments, the aluminum is evaporated onto the front surface of the glass rather than on the back, in order to eliminate faint reflections from the glass itself. When light falls on a body some of the light may be reflected, some absorbed, and some transmitted through the body. In order for a smooth surface to act as a mirror, it must reflect as much of the light as possible and must transmit and absorb as little as possible. In order to reflect light rays without scattering or diffusing them, a mirror's surface must be perfectly smooth or its irregularities must be smaller than the wavelength of the light being reflected. (The wavelengths of visible light are on the order of 5 10-5 cm.) Mirrors may have plane or curved surfaces. A curved mirror is concave or convex depending on whether the reflecting surface faces toward the centre of curvature or away from it. Curved mirrors in ordinary usage have surfaces that are spherical, cylindrical, paraboloidal, ellipsoidal, and hyperboloidal. Spherical mirrors produce images that are magnified or reduced--exemplified, respectively, by mirrors for applying facial makeup and by rearview mirrors for automobiles. Cylindrical mirrors focus a parallel beam of light to a line focus. A paraboloidal mirror may be used to focus parallel rays to a real focus, as in a telescope mirror, or to produce a parallel beam from a source at its focus, as in a searchlight. An ellipsoidal mirror will reflect light from one of its two focal points to the other, and an object situated at the focus of a hyperboloidal mirror will have a virtual image. Mirrors have a long history of use both as household objects and as objects of decoration. The earliest mirrors were hand mirrors; those large enough to reflect the whole body did not appear until the 1st century AD Types of mirror

There are many types of glass mirrors, each representing a different manufacturing process and reflection type. An aluminium glass mirror is made of...
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