Plane mirror

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.

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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 shape and size as the object it is reflecting.

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 extremely large.

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