We see objects (with the exception of self-luminous objects) by reflected light.

If the surface of the body is irregular, the reflection will be irregular or diffuse. The reflected beam of light therefore carries information about the nature (as well as the colour) of the surface.

A highly polished, smooth surface (for example, a mirror) reflects light in a more regular way. The light reflected by a plane (flat) mirror does not contain information about the mirror itself: when you look into a mirror you see "yourself" not the mirror.

Image Formation by a Plane (Flat) Mirror

A ray diagram with rays of light obeying the law of reflection of light (as above) shows why the image formed by a plane mirror is the same perpendicular distance behind the mirror as the object is in front of the mirror.

This type of image is called a virtual image because it is formed at a place where there is no light from the object. The mirror simply makes the light appear to be coming from behind it.

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