Plane mirror

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A plane mirror is a mirror with a planar reflective surface. For light rays striking a plane mirror, the angle of reflection equals the angle of incidence. Thus a collimated beam of light does not spread out after reflection from a plane mirror, except for diffraction effects.

[edit] Images

A plane mirror makes images of objects in front of it; these images appear to be behind the plane in which the mirror lies. A straight line drawn from part of an object to the corresponding part of its image makes a right angle with, and is bisected by, the surface of the plane mirror. The image formed by a plane mirror is always virtual (meaning that the light rays do not actually come from the image), upright, and of the same size as the object it is reflecting.

[edit] Relation to curved mirrors

Mathematically, a plane mirror can be considered to be the limit of either a concave or a convex spherical curved mirror as the radius, and thus also the focal length, of the spherical mirror become very large.