What is the angle of incidence?

The angle of incidence is defined as the angle formed between the direction of an incoming wave, such as light, and a line that is perpendicular to the surface it is striking. This perpendicular line is often referred to as the normal line. When light rays hit a surface, understanding the angle at which they approach is crucial for determining how they will behave upon interaction with that surface, including reflection and refraction.

In contexts like optics or wave mechanics, this definition helps in predicting various phenomena, such as Snell's Law, which describes how light bends when it moves from one medium to another. The angle of incidence plays a key role in these interactions by influencing the behavior of light upon striking interfaces. Thus, the definition aligning with the angle between the wave direction and the perpendicular line accurately characterizes the concept of angle of incidence.