mirror /mir·ror/ (mir´er) a polished surface that reflects sufficient light to yield images of objects in front of it.
mirror
dental mirror mouth m.
frontal mirror , head mirror a circular mirror strapped to the head of the examiner, used to reflect light into a cavity, especially the nose, pharynx, or larynx.
mouth mirror a small mirror attached at an angle to a handle, for use in dentistry.
Mirror
noun An archiving device written to more than one hard disk simultaneously, so that if one disk fails, the computer continues to function without loss of data
verb To maintain an exact copy of a file or database
verb To maintain an exact copy of a file or database
mirror
A surface capable of reflecting light rays and forming optical images. Such surfaces are smooth or polished, made of highly polished metal, or a thin film of metal (e.g. aluminium) on glass, quartz or plastic. Object distance l and image distance l′ relate to the focal distance f or the radius of curvature r of the mirror, as follows
2/r represents the refractive power of the mirror, in air. If the medium that contains the incident and reflected rays is n, the power becomes F = 2n/r and the focal length, f = r/2n (Fig. M12). See focal length; fundamental paraxial equation; catadioptric system.
back surface mirror A mirror which reflects from the back surface of a refracting layer, usually glass. See front surface mirror.
concave mirror A mirror with a spherical concave surface forming an erect, magnified, virtual image when the distance from the mirror is less than the focal distance and an inverted real image when the object distance is greater than the focal distance (Fig. M12).
convex mirror A mirror with a spherical convex surface forming a virtual, erect and diminished image (Fig. M12).
front surface mirror A mirror that reflects directly from its front surface. The advantages of this type are that, unlike back surface mirrors, there is no chromatic effect as the glass is not used optically, therefore ultraviolet rays can be used which would otherwise be absorbed in the glass and there is no ghost reflection from the front surface. However, these mirrors can be easily scratched and the coating may tarnish. Often a coating of silicon monoxide is evaporated on top of the surface, but this causes a loss of reflectivity. See ghost image; back surface mirror.
plane mirror A mirror whose surface is plane and forms a virtual image of the same size as the object. Object and image distances are equal.
semi-silvered mirror See beam splitter.
mirror writing Writing backward, Latin letters being written from right to left and the details of the letters reversed. The writing thus appears normal when viewed in a mirror. Syn. retrography.
back surface mirror A mirror which reflects from the back surface of a refracting layer, usually glass. See front surface mirror.
concave mirror A mirror with a spherical concave surface forming an erect, magnified, virtual image when the distance from the mirror is less than the focal distance and an inverted real image when the object distance is greater than the focal distance (Fig. M12).
convex mirror A mirror with a spherical convex surface forming a virtual, erect and diminished image (Fig. M12).
front surface mirror A mirror that reflects directly from its front surface. The advantages of this type are that, unlike back surface mirrors, there is no chromatic effect as the glass is not used optically, therefore ultraviolet rays can be used which would otherwise be absorbed in the glass and there is no ghost reflection from the front surface. However, these mirrors can be easily scratched and the coating may tarnish. Often a coating of silicon monoxide is evaporated on top of the surface, but this causes a loss of reflectivity. See ghost image; back surface mirror.
plane mirror A mirror whose surface is plane and forms a virtual image of the same size as the object. Object and image distances are equal.
semi-silvered mirror See beam splitter.
mirror writing Writing backward, Latin letters being written from right to left and the details of the letters reversed. The writing thus appears normal when viewed in a mirror. Syn. retrography.
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Fig. M12 Image of an object O formed in A, a concave mirror and B, a convex mirror. Four rays are drawn in each case for completeness, but two would suffice (C, centre of curvature; F′, focal point; f′, focal length; l and l′, object and image length; r, radius of curvature)
mirror
Informatics noun An archiving device written to more than one hard disk simultaneously, so that if one disk fails, the computer continues to function without loss of data verb To maintain an exact copy of a file or
database. See FTP, Web Paranormal See Mind mirror.
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