The normal, angles of incidence, reflection & refraction

About the normal, angles of incidence, reflection & refraction

• • The angles of incidence and reflection and refraction are measured between a ray of light and an imaginary line called the normal.

If one line is normal to another, then it is at right angles to it.

In geometry, normal (a or the normal) refers to a line drawn perpendicular to a given line, plane or surface.

• • The way in which a normal appears in a geometric drawing depends on the circumstances:
    • • When light strikes a flat surface or plane, or the boundary between two surfaces, the normal is drawn perpendicular to the surface, forming a right angle (90°) with it.
      • When light hits a curved surface, the normal line is drawn straight up from the point where the light hits the surface.
      • If light travels directly through the centre of a sphere, the normal line also passes through the centre of the sphere.
      • When a normal is drawn on a ray-tracing diagram, it provides a reference perpendicular to the surface against which changes in direction of light can be measured.