A ray diagram shows how light travels, including what happens when it reaches a surface. In a ray diagram, you draw each ray as:
Remember to use a ruler and a sharp pencil.
When light reaches a mirror, it reflects off the surface of the mirror:
In the ray diagram:
The law of reflection states that the angle of incidence equals the angle of reflection, i = r. It works for any angle. For example:
In the second example, if a light ray travelling along the normal hits a mirror, it is reflected straight back the way it came. The reflection of light from a flat surface such as a mirror is called specular reflection – light meeting the surface in one direction is all reflected in one direction.
If light meets a rough surface, each ray obeys the law of reflection. However, the different parts of the rough surface point in different directions, so the light is not all reflected in one direction. Instead, the light is reflected in all directions. This is called diffuse scattering. It explains why you can see a clear image of yourself in a shiny flat mirror, but not in a dull rough wall.