OPTICS!
 If a charge is accelerated at frequency f, it loses energy and momentum by creating photons, which carry away KE = hf, and momentum p = KE/c, where the constant h is 4.13 x 10-15 eV-sec and c is 3 x 108 m/s. Photons, like all bosons, are created from nothing, when the appropriate “coupling constant” is present. In the case of photons, the coupling constant is charge.
 Roger Bacon (1214? - 1294) continued the work of Ibn al Haytham on optics and was the first person to do demonstrations of physical processes in the classroom.

In the 18th and 19th Centuries it was established beyond doubt that light behaved like a wave. In 1905 the fact that light actually consists of particles was demonstrated. In 1920, it was realized that any particle described by quantum physics, which has a definite energy and momentum, is described as a wave of probability, with frequency f = KE/h and wavelength λ = h/p. In drawing processes involving light, it is usually far easier to draw a ray, a line perpendicular everywhere to the advancing wavefronts, rather than to try to draw the wave itself.