Wave - Particle Duality

Dual Nature of Light

Some of the properties of light like diffraction and interference can be explained on the basis of its wave nature. On the other hand, some other properties like photoelectric effect and scattering of light can be explained only on the basis of particle nature of light. Thus, light has a dual nature possessing the properties of both a wave and a particle. Light could under some conditions behave like a particle and other conditions behave as a wave.

de-Broglie Wavelength

In 1923, Louis de Broglie argued that if light can show wave as well as particle nature, why should particles of matter (electrons) not possess wave like characteristics. He proposed that matter particles should indeed have a wave nature and said that a particle of mass m moving with a velocity v has an associated wavelength, λ (de Broglie wavelength).

λ = h/mv or λ = h/p

The de Broglie wavelength of a body is inversely proportional to its momentum. Since the magnitude of h is very small, the wavelength of the objects of everyday world would be too small to be observed.

Electron Diffraction

If the electrons show wave nature, then a beam of these electrons is expected to show diffraction which is a property of waves. In 1927, G.P. Thomson and C.J. Davisson demonstrated the diffraction of electron waves by the crystal lattice of nickel.

Thus, electrons also show a dual nature. That is, sometimes these show particle nature while at some other times they show wave nature.