14.1.A.1 A light ray is a straight line that is perpendicular to the wave front of a light wave and points in the direction of travel of the wave.
14.1.A.1.i Light rays can be used to determine the behavior of light in geometric optics, where the wave nature of light can be neglected.
14.1.A.1.ii Rays are not sufficient to understand the spreading of light. In interference and diffraction, the wave nature of the light is important.
14.1.A.2 Ray diagrams depict the path of light before and after an interaction with matter.