1 diffuse scattering When light is reflected off a surface in all directions. 2  dispersion Spreading out of the different wavelengths of light, caused by refraction of light as it passes through a prism. 3  frequency The number of waves produced each second.4  The unit of frequency is hertz, 'Hz'.n the ray diagram: 1  the hatched vertical line on the right represents the mirror. 2  the dashed line is called the normal, drawn at 90° to the surface of the mirror. 3  the angle of incidence, i, is the angle between the normal and incident ray. 4  the angle of reflection, r, is the angle between the normal and reflected ray.