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Reflection of Light
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.
 
If a narrow beam of light is directed towards a mirror, it can easily be verified that the angle of reflection, r is always equal to the angle of incidence, i.
This observation is often called the law of reflection of light (but can, in fact, be observed in many other waves).
Notice that, in optics, we (nearly) always measure angles from a perpendicular (or normal line) to the surface of interest.
 
Image Formation by a Plane (Flat) Mirror
In order to see where an object will appear to be when viewed in the mirror, we simply need to trace the paths of (at least) two rays of light, leaving a given point on the object (a candle flame, in this case).
We draw those rays obeying the law of reflection and find that the rays entering the person's eye are exactly as they would be if coming from a point behind the mirror.
 
Simple geometry (or a carefully drawn diagram, as here) shows that 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.
It is fair to describe the mirror as performing a simple optical illusion.
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