Overview
This lecture explains wave reflection at boundaries, introduces ray diagrams, and compares specular and diffuse reflection.
Reflection at Boundaries
- When a wave hits a boundary, it can be absorbed, transmitted (leading to refraction), or reflected.
- Whether absorption, transmission, or reflection occurs depends on wave wavelength and material properties.
- Reflected waves do not enter the new material, instead bouncing off the surface.
Ray Diagrams and the Law of Reflection
- Ray diagrams visually represent wave reflection.
- Always start ray diagrams by drawing the boundary between two materials.
- The incoming ray should have an arrow pointing toward the boundary.
- Draw the "normal," a dashed line perpendicular (90°) to the surface, at the point of incidence.
- The angle of incidence is measured between the incoming ray and the normal.
- The Law of Reflection states: angle of incidence = angle of reflection.
- The reflected ray leaves the boundary at the same angle to the normal as the incoming ray.
Types of Reflection
- Specular reflection occurs on smooth, flat surfaces (like mirrors), where light rays reflect in one direction, creating clear images.
- Diffuse reflection occurs on rough surfaces (like paper), where normals point in different directions, scattering reflected rays.
- Both reflection types obey the law: angle of incidence equals angle of reflection.
Key Terms & Definitions
- Boundary — the surface between two materials where a wave can be absorbed, transmitted, or reflected.
- Normal — a line perpendicular (90°) to the surface at the point where the wave hits the boundary.
- Angle of Incidence — the angle between the incoming wave and the normal.
- Angle of Reflection — the angle between the reflected wave and the normal.
- Point of Incidence — the point where the incoming ray meets the boundary.
- Specular Reflection — reflection from a smooth surface with all rays reflected in the same direction.
- Diffuse Reflection — reflection from a rough surface with rays scattered in different directions.
Action Items / Next Steps
- Practice drawing ray diagrams and labeling normals, angles, and rays.
- Review the law of reflection and be able to apply it to different scenarios.
- Be prepared to measure angles of incidence and reflection using a protractor for exam questions.