Which term describes the angle at which light hits a surface, measured with respect to the normal?

• A. Angle of Reflection
• B. Normal
• C. Angle of Incidence
• D. Angle of Refraction

Answer: (C)

The angle of incidence is the angle between the incoming light ray and the line perpendicular to the surface at the point of contact. That perpendicular line is called the normal, and it serves as the reference for measuring both the incident and reflected (and refracted) directions. This angle is central because it governs how light behaves at a boundary: the incoming ray makes a certain angle with the normal, and the law of reflection states the reflected ray makes the same angle with the normal. If light enters a different medium, the direction changes according to Snell’s law, yielding the angle of refraction, which is measured from the normal in the second medium. A zero angle of incidence occurs when the light hits straight on, perpendicular to the surface.