Introduction to using massive particles (electrons, neutrons) for diffraction. The de Broglie relation relates the momentum of a particle to its wavelength. Time 3:46.
Abstract In 1925, de Broglie hypothesized that any material particle has an associated wave with /h p . Electron diffraction seems to support that Hypothesis. But then, the electron at rest will have infinite wavelength, and infinite wave phase velocity. This says that for a material particle, the de Broglie relation does not hold. Failed attempts to save the postulate, kept the flawed relation, and modified the waves into train waves, pilot waves, probability waves, … to name a few. We keep the de Broglie waves unchanged, and modify the relation. First, we observe that the Planck energy E h used by de Broglie defines virtual electromagnetic waves. Consequently, for any particle, the virtual electromagnetic wavelength is / /c h mc , and / /h m c . Refinement of de Broglie argument, indicates that /h mmay be x , Heisenberg’s uncertainty in the particle location. de Broglie’s later analysis supports this interpretation, and we offer an explanation to particle diffraction as a consequence of Heisenberg’s uncertainty. We apply / /h m c to obtain the dispersion relations for the de Broglie virtual waves.
This chapter describes the dual nature of electron/de Broglie waves. de Broglie suggested that like light, an electron also behaves as both a particle and a wave. Based on this hypothesis, a relationship between wavelength of electrons (a particle) and momentum was developed. It opines that ‘wavelength of the particle is inversely proportional to momentum’. This is called the de Broglie relation. On the basis of the above facts, we have developed a relationship between wavelength and voltage applied and this relation may be stated as ‘the wavelength of a particle is inversely proportional to the square root of the voltage applied to the system’. This chapter also uses the Davisson and Germer experiment to show the wave nature of the particle, i.e., diffraction of electrons by crystal lattice. The experimental results were the same as found in the case of the diffraction of X-ray by crystals. This chapter also provides an idea on quantisation of angular momentum. It also discusses Heisenberg’s uncertainty principle, phase velocity, group velocity, and uncertainty relation between energy and time. The chapter comprises the experimental evidence of Heisenberg’s uncertainty principle, such as by diffraction of electrons through a slit and gamma ray microscope thought experiment, which is shows the physical significance of the uncertainty principle. Sufficient references, solved problems, and questions on concepts have been provided at the end of chapter.
The de Broglie relation serves as a foundational pillar connecting classical linear momentum with quantum mechanical wave properties. For massive particles moving at relativistic speeds, momentum is routinely expressed using the Lorentz factor, yielding a direct identity with the quantum wave parameters. However, when applied to massless particles such as photons traveling at the speed of light, this product encounters an indeterminate mathematical form. This paper demonstrates how the general relativistic energy momentum dispersion relation resolves this breakdown. Through two detailed numerical case studies involving a relativistic electron moving at sixty percent of light speed and a green photon, it shows that while the algebraic expression relying on rest mass fails for massless entities, the underlying physical equivalence between momentum and wavelength remains globally valid across all particle regimes.
In the previous chapter we have seen that electrons and other subatomic particles sometimes exhibit properties similar to those commonly associated with waves: for example, electrons of the appropriate energy are diffracted by crystals in a manner similar to that originally observed in the case of x-rays. We have also seen that the energy and momentum of a free particle can be expressed in terms of the angular frequency and wave vector of the associated plane wave by the de Broglie relations (4.8).