1. Law of Reflection and Plane Mirrors

2. The angle of reflection is equal to the angle of incidence
incident ray
normal
reflected ray
40o
40o
reflecting surface
point of incidence
The First Law of Reflection: The angle of incidence equals the angle of reflection.
Angles are measured from the normal, NOT from the reflecting surface.

3. The Law of Reflection
incident ray
normal
reflected ray i r
reflecting surface
point of incidence
The angle of reflection (r) is equal to the angle of incidence (i).
The reflected ray and the incident ray are on opposite sides of the normal.
The incident ray, reflected ray, and normal are all on the same plane.

4. Law of Reflection - Key Terms
Incident ray – the light ray travelling toward the mirror
(or reflecting surface)
Reflected ray – the light ray that has ‘bounced’ off a
reflecting surface
Normal – line perpendicular to a surface such as a mirror
Angle of incidence (i) – the angle between the incident
ray and the normal
Angle of reflection (r) – the angle between the reflected

5. Types of Reflection
When more than one incident light ray reflect off a surface, the laws of reflection still hold but the surface effects the way you see the reflected rays.
Specular reflection
reflection of light off a smooth, shiny surface.
Example: plane mirror, disco ball
Diffuse reflection
reflection of light off an irregular or dull surface.
Example: rough aluminum foil, rough lake

6. Drawing Normals
Use a protractor and ruler to draw normals to the lines at each of the points shown.

7. Same Plane

8. Disco Ball – Specular Reflection

9. Reflecting Lake – Diffuse Reflection