6.1.2 Describing Wave Motion

Reflection and Refraction

Reflection

Reflection

Reflection occurs when a wave bounces off a material boundary. The key rule for reflection is:

$$angle of incidence=angle of reflection$$

• The angle of Incidence: The angle between the incoming wave and the normal line to the boundary.
• The angle of Reflection: The angle between the reflected wave and the normal line to the boundary.
• Normal Line: A line drawn perpendicular (at right angles) to the boundary. The diagram shows reflection on a wave diagram. Wave diagrams are used to show the path of waves. Straight lines are used to represent the path of the wave and arrows represent the direction of travel of the wave. The normal is drawn as a dotted line.

Specular and Diffuse Reflection

Reflection can be either specular or diffuse.

• Specular Reflection: Occurs when waves bounce off a smooth surface, reflecting at the same angle. This produces a clear, shiny reflection, like light reflecting off a mirror.
• Diffuse Reflection: This happens when waves hit a rough surface, causing them to reflect at different angles due to the surface's irregularities. Even though the angle of incidence still equals the angle of reflection for each wave, the roughness scatters the reflections, making the surface appear matte without a clear reflection.

Refraction

Waves are only refracted if the wave meets the boundary at an angle. The amount the wave changes direction depends on the difference in the materials it is travelling between. This is because waves travel at different speeds in different materials.

• If the wave speeds up in the new material, it bends away from the normal.
• If the wave slows down in the new material, it bends toward the normal.