Angle of incidence

The angle of incidence is the angle between a ray of incoming light (or any wave) and a line perpendicular to the surface it hits, called the normal. Imagine shining a flashlight at a mirror; if the light hits straight on, the angle of incidence is zero. If it hits at a slant, the angle increases. This concept helps scientists understand how light behaves when it strikes surfaces, influencing reflection, refraction, or absorption. Essentially, it's a measure of how "steep" the incoming wave is relative to the surface’s perpendicular line.