The angle between the normal and the incident ray
Explanation
In the study of ray optics, the reflection of light is analyzed using specific geometric parameters defined at the point where a light ray strikes a surface.
Definition of Angle of Incidence:
- The angle of incidence is defined as the angle formed between the incident ray and the normal to the reflecting surface at the point of incidence.
- The normal is an imaginary line drawn perpendicular ($90^\circ$) to the surface at the point where the light ray hits.
Analysis of Other Angles:
- The angle between the incident ray and the reflected ray: The angle between the incident ray and the reflected ray is the sum of the angle of incidence and the angle of reflection ($i + r$).
- The angle between the incident ray and the reflecting surface: The angle between the incident ray and the reflecting surface is known as the glancing angle. It is complementary to the angle of incidence ($90^\circ - i$).
- The angle between the normal and the reflected ray: The angle between the normal and the reflected ray is defined as the angle of reflection ($r$).
Key Takeaway:
In optics, angles (incidence, reflection, and refraction) are always measured relative to the normal, not the surface. According to the laws of reflection, the angle of incidence is equal to the angle of reflection ($\angle i = \angle r$).