ABSTRACT
This chapter describes how the wave nature of electromagnetic radiation can be justified, even when the nature of the source cannot be described. A well-known wave property is that of interference. The arithmetic sum of two identical waves is zero when the peaks of one coincide with the troughs of the other. This condition is called destructive interference. The two waves travel different distances. An observer at point A will see the arithmetic sum of the two reflected waves. If the extra path length is half a wavelength, the resultant amplitude will be zero – interference is destructive – because the two waves will be completely out of phase. The bending of the light path by a lens is called refraction and is a wave property. There is a limit to the useful magnification of any optical device and it is set by several factors.
