Glossary
Angle of incidence
The angle formed between an incoming light ray and the normal (a line perpendicular to the surface) at the point where the ray strikes.
Example:
When sunlight hits a window, the angle of incidence is measured from the incoming ray to the imaginary line perpendicular to the glass.
Angle of reflection
The angle formed between the outgoing (reflected) light ray and the normal (a line perpendicular to the surface) at the point of reflection.
Example:
After light bounces off a mirror, the angle of reflection describes how far the reflected ray deviates from the normal.
Diffuse reflection
Reflection that occurs when light strikes a rough or irregular surface, causing the incident light rays to scatter in many different directions.
Example:
The reason you can see a book from any angle is due to diffuse reflection off its paper surface.
Geometric optics
A simplified model of light that treats light as rays traveling in straight lines, ignoring its wave nature to analyze phenomena like reflection and refraction.
Example:
Using a ruler and protractor to trace light paths through lenses in a lab experiment is an application of geometric optics.
Law of reflection
A fundamental principle stating that the angle of incidence is equal to the angle of reflection.
Example:
If a flashlight beam hits a mirror at a 30° angle to the normal, the law of reflection dictates it will bounce off at 30° to the normal.
Light ray
A straight-line path that light travels in a specific direction, used to represent the direction of light propagation in geometric optics.
Example:
When a laser pointer shines across a dark room, the visible beam illustrates a single light ray.
Normal
An imaginary line drawn perpendicular (at 90 degrees) to a surface at the exact point where a light ray strikes it.
Example:
When drawing a ray diagram for a mirror, the normal helps you accurately measure the angles of incidence and reflection.
Ray diagrams
Visual tools that use light rays to illustrate how light interacts with surfaces like mirrors or lenses, showing its path before and after interaction.
Example:
Students often draw ray diagrams to predict where an image will form when light reflects off a curved mirror.
Reflection
The phenomenon where light bounces off a surface and returns into the medium from which it originated.
Example:
Seeing your face in a still pond is an example of light undergoing reflection from the water's surface.
Specular reflection
Reflection that occurs when light strikes a smooth, polished surface, causing incident light rays to reflect uniformly in a single direction.
Example:
A perfectly clear image of the sky on a calm lake is a classic example of specular reflection.