(a) De-Broglie suggested that non-radiation of energy by the electrons circling in a Bohr’s orbit can be explained on the basis on the basis of the formation of stationary waves by the electrons in circular motion in Bohr’s orbits.
(b) Comparing this to the vibrations of a wire loop such stationary waves would be formed if each wave joins smoothly with the next.
(c) In other words the number of wavelengths must be an integer.
