Reflection

Objective: Use incident and reflected angles relative to a normal.

In a ray model of specular reflection from a smooth surface, angle of incidence equals angle of reflection when both are measured from the surface normal. A ray striking at 30° from the normal reflects at 30° on the other side of the normal. Diffuse reflection from a rough surface still follows local reflection at small facets but scatters rays in many directions. A mirror’s image is formed by the geometry of reflected rays, not by light emerging from behind the mirror. Ray diagrams are useful when wavelength is small compared with structures; wave behavior becomes important in other regimes. Distinguish angles from the normal versus from the surface.

Objective: Apply reflection to calculations, evidence, and specified situations.

For specular reflection at a smooth surface, incidence and reflection angles are equal and measured from the normal. A plane mirror forms a virtual image at the same distance behind the mirror as the object lies in front. The reflected rays do not physically pass through that apparent image location. Diffuse reflection from rough surfaces still follows local reflection geometry but spreads rays in many directions. A time graph is not a ray diagram; use actual surface geometry for angles.