Introduction - Wave nature of particles

A wave, in the classical sense, is described by its frequency, wavelength, wave velocity, amplitude and intensity, and it spreads out to occupy a relatively large region of space. A particle, by contrast, is described by its mass, velocity, momentum and energy, and occupies a single, definite, very small region of space at any instant. Classical physics treated these as two utterly distinct categories of physical entity -- but the quantum theory built up through sections 7.1 and 7.2 has already shown that radiation carries a dual character, behaving as a wave at some times and as a particle at others. …