How is the angle of reflection defined?

The angle of reflection is defined as the angle between the incoming wave and the perpendicular (normal) line to the surface at the point of reflection. When a wave, such as light or sound, strikes a surface, it reflects off that surface at an angle equal to the angle at which it arrived, according to the law of reflection. This principle is crucial in understanding how waves behave upon interacting with different surfaces, whether they are mirrors, water, or other materials.

The correct definition highlights the specific relationship between the incoming wave's direction and the surface's normal, which is essential for predicting how waves will behave in various scenarios, such as in optics or acoustics. Other options do not pertain directly to the concept of reflection or involve different physical phenomena, making them less relevant to the definition of the angle of reflection.