- 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, so at a right angle (900) to the boundary.
- When light strikes a curved surface or plane, the normal is drawn at a tangent to the boundary.
- When light strikes a sphere in line with its centre of the sphere and passes straight through without deviation then the normal follows the same line.
- Light travels in a straight line through a vacuum or a transparent medium such as air, glass, or still water.
- When light encounters an obstacle or passes from one transparent medium to another, it can result in a variety of optical phenomena including absorption, dispersion, diffraction, polarization, reflection, refraction, scattering or transmission.
- Geometry can be used to calculate the outcome of light encountering different optical phenomena.
- When a normal is drawn on a ray-tracing diagram, it provides a reference against which changes in direction of light can be measured.