De Broglie in 1923 suggested that wave particle duality must be universal, that is all material particles should also display a dual wave particle behavior. To put it in other words all material particles, just like photons can have wave like aspects. Let is consider a photon of frequency . Then its energy is given by where m is the mass of the photon particle. This photon travels with the velocity of ling c and its momentum is given by
Putting this value in above equation we get
De Broglie assumed that equation (1) is valid for material particles like electrons. We can generalize each material particle with momentum behaves like a group of matter waves whose wavelength and wave vector k such that
Equation (1) and (2) are known as de Broglie relation which connects momentum of particle with the wavelength and wave vector of the wave corresponding to the particle.