1. Reflection

2. Interface  Plane waves at an interface may be absorbed. Discontinuity in materials Different permittivity Scattered wavelets cancel  Materials can be opaque or translucent.

3. Backscatter  At a discontinuity some of the backwards scattered waves coincide.  This is called reflection. Present at all interfaces  Reflected waves also form rays.

4. Mirror Glass  Clear materials also reflect at an interface.  About 4% of the light energy is reflected at an air-glass interface. Significant if one side is darkerSignificant if one side is darker Photo by Michael Goltz Photo from visit-Chicago- Illinois.com

5. Specular Reflection  If a surface is smooth then the reflected rays travel in parallel.  This is called specular reflection.

6. Diffuse Reflection  If the surface is rough then reflected rays travel in different directions.  This is called diffuse reflection.

7. Measuring Reflection  Geometry describes a single ray reflected from a surface.  The normal is a line perpendicular to the surface at the point the ray strikes.  Angles are measured with respect to the normal. Incident angle  iIncident angle  i Reflected angle  rReflected angle  r

8. Laws of Reflection  The relationship of the angles are called the laws of reflection. Incident ray, reflected ray and the normal are all in the same planeIncident ray, reflected ray and the normal are all in the same plane Angle of reflection equals the angle of incidence: θ i = θ rAngle of reflection equals the angle of incidence: θ i = θ r next