Reflection
Describe light as a ray.
- A light ray is a straight line that is perpendicular to the wavefront of a light wave and points in the direction of travel of the wave.
- Light rays can be used to determine the behavior of light in geometric optics, where the wave nature of light can be neglected.
- Rays are not sufficient to understand the spreading of light. In interference and diffraction, the wave nature of the light is important.
- A laser is a common source of a single coherent, monochromatic beam of light that can be modeled as a ray. The wave nature of lasers will be considered in Unit 14.
- Ray diagrams depict the path of light before and after an interaction with matter.
Describe the reflection of light from a surface.
- Light that is incident on a surface can be reflected.
- The law of reflection states that the angle between the incident ray and the normal (the line perpendicular to the surface) is equal to the angle between the reflected ray and the normal. Relevant equation:
- Diffuse reflection is the reflection of light from a rough surface and results in light reflected in many different directions, because the line normal to the surface varies over the area over which the light is incident.
- Specular reflection is the reflection of light from a smooth surface and results in light uniformly reflected from the surface, because the line normal to the surface has an approximately constant direction over the area the light strikes.