Bohr in his theory has assumed that an electron is a material particle revolving around the nucleus in circular orbits. But De Broglie in 1924 pointed out that the electron-like light exhibits wave as well as particle nature, i.e, an electron has a dual character. This concept of the dual character of matter gave birth to the wave mechanical theory of matter according to which the electrons, protons, and even atoms when in motion possess all wave properties.
De Broglie derived a relationship for the calculation of wavelength (λ) of the wave associated with a particle of mass m moving with velocity v as given below:
λ = h/mv
or λ = h/p [ ∴ p = mv = momentum of the particle ]
h = Plank’s constant
m = mass of the particle
v = velocity of the particle
Although the De Broglie equation is true for all particles in motion, i.e, whether small or large, the concept of wave-particle duality is of real importance in the case of very small particles like electrons, and it is insignificant for the large particles because in such case the De Broglie wavelength is too small to measure.