18.5 Wave-Particle Duality
Interference and diffraction of light provide evidence for its wave nature, while photoelectric effect and Compton effect prove the particle nature of light. Similarly, the experiments of Davisson and Germer and G. P. Thomson reveal wave-like nature of electrons and in the experiment of J. J. Thomson to find , we had to assume particle-like nature of the electron. In the same ways we are forced to assume both wave-like and particle-like properties for all matter: electrons, protons, neutrons, molecules, etc., and also light, X-rays, -rays, etc. have to be included in this. In other words, matter and radiation have a dual 'wave-particle' nature and this new concept is known as wave-particle duality. Niels Bohr pointed out in stating his principle of complementarity that both wave and particle aspects are required for the complete description of both radiation and matter. Both aspects are always present and either may be revealed by an experiment. However, both aspects cannot be revealed simultaneously in a single experiment. The two aspects of light are different 'faces' that light shows to experimenters. A particular aspect is determined by the nature of the experiment being done. If we put a diffraction grating in the path of a light beam, we reveal it as a wave. If we allow the light beam to hit a metal surface, we need to regard the beam as a stream of particles to explain our observations. There is no simple experiment that we can carry out with the beam that will require us to interpret it as a wave and as a particle at the same time. Light behaves as a stream of photons when it interacts with matter and behaves as a wave in traveling from a source to the place where it is detected. Thus, the duality of light had to be accepted as a fact of life. In effect, all micro-particles (electrons, protons, photons, atoms, etc.) propagate as if they were waves and exchange energies as if they were particles - that is referred to as the wave-particle duality.
Do you know?
lightbulb(a) If electrons behaved as discrete particles with no wave properties, they would pass through one or the other of the two slits and strike the screen causing it to glow and produce exact images of the slits. (b) In reality, the screen reveals a pattern of bright and dark fringes similar to light is used and interference occurs between the light waves coming from each slit.