This chapter discusses some of the experiments that provided evidence that light, which we have recognized as a wave phenomenon, has properties that we normally associate with particles. It explains these phenomena and to understand the physical processes involved, some kind of a corpuscular theory of light is required. The chapter discusses briefly how the idea of the existence of discrete structures has been innovated in physics. The first idea of the existence of discrete structures referred to physics of materials and their electric properties. In a different area of physics, radiation spectroscopy experiments show that light emitted by hot solid or liquid exhibits a continuous spectrum. The chapter focuses on that the results of the experiments on photoelectric effect are in contradiction to classical wave theory. The wave theory of light leads one to anticipate that a long-wavelength light incident on a surface could cause enough energy to be absorbed for an electron to be released.
This chapter discusses some of the experiments that provided evidence that light, which we have recognized as a wave phenomenon, has properties that we normally associate with particles. It explains these phenomena and to understand the physical processes involved, some kind of a corpuscular theory of light is required. The chapter discusses briefly how the idea of the existence of discrete structures has been innovated in physics. The first idea of the existence of discrete structures referred to physics of materials and their electric properties. In a different area of physics, radiation spectroscopy experiments show that light emitted by hot solid or liquid exhibits a continuous spectrum. The chapter focuses on that the results of the experiments on photoelectric effect are in contradiction to classical wave theory. The wave theory of light leads one to anticipate that a long-wavelength light incident on a surface could cause enough energy to be absorbed for an electron to be released.
This chapter provides a basis for an insight into the nature of quantum effects. The Newtonian approach cannot explain diffraction phenomena. The wave theory of the nature of light proposed by Huygens was able to account for these phenomena as well as for geometric optics. Planck was not only able to overcome the difficulties encountered by his predecessors, but included their findings as special cases of his analysis. Planck considered that the radiating surface was composed of electric dipole oscillators, and that a relationship should exist between the energy of the radiation and the frequency of the oscillators. According to classical theory a continuous spectrum is expected when matter is excited by an arc, or spark, as in spectroscopy. It is found experimentally that only “lines”, or discrete radiations, occur when the light is diffracted. Bohr’s revolutinary ideas provided a significant portion of the bases for the modern understanding of spectra and, consequently, of atomic structure.
Light occupies a special position in our attempts to understand nature both classically and quantum mechanically. We recall that Newton, who made so many fundamental contributions to optics, championed a particle description of light and was not favorably disposed to the wave picture of light. However, the beautiful unification of electricity and magnetism achieved by Maxwell clearly showed that light was properly understood as the wave-like undulations of electric and magnetic fields propagating through space. The central role of light in marking the frontiers of physics continues on into the twentieth century with the ultraviolet catastrophe associated with black-body radiation on the one hand and the photoelectric effect on the other. Indeed, it was here that the era of quantum mechanics was initiated with Planck's introduction of the quantum of action that was necessary to explain the black-body radiation spectrum. The extension of these ideas led Einstein to explain the photoelectric effect, and to introduce the photon concept. It was, however, left to Dirac to combine the wave-and particlelike aspects of light so that the radiation field is capable of explaining all interference phenomena and yet shows the excitation of a specific atom located along a wave front absorbing one photon of energy. In this chapter, following Dirac, we associate each mode of the radiation field with a quantized simple harmonic oscillator, this is the essence of the quantum theory of radiation.
Quantum field theory describes the particle nature of electromagnetic radiation using the "photon," but has never explained why a fundamental particle exhibits such perfect wave behavior. This paper provides a complete alternative explanation: the photoelectric effect, Compton scattering, and antibunching experiments — landmark experiments considered proof of photon particle nature — require no photon concept. Quantization is not a property of light itself, but of the discrete energy level structure governing how bound electrons emit and absorb energy. Light remains a continuous transverse wave; discreteness results from electrons as "prisoners" in atomic "cages" that can only transition between specific energy steps. Waves propagate continuously and are emitted and absorbed in quantized form — the photon is not a particle, but the name of an energy-exchange event.
The photoelectric effect, the Compton effects, and now anticorrelation experiments have been claimed to prove that light consists of particles flying through a void. However the particle model is decisively falsified by the known wave qualities of electromagnetic radiation. Quantum Electrodynamics also uses spreading wave amplitudes; not flying particles. The evidence indicates that light is a wave and electrons are electromagnetic wave-structures that absorb and emit light in discrete wave-packets. These wave-quanta are emitted directionally and then spread in space in proportion to their wavelength. Their waves superposition with all other waves in space. In low intensity experiments, the waves that an electron in a photodetector absorbs come from the superpositioning of the source wave-quanta and background radiation. The importance of background radiation is evidenced by "dark counts". Treating electrons and the quanta they absorb and emit as particles when they are composed of waves is the source of all the paradoxes, unreality and confusion in Quantum Mechanics. The word "photon" should be replaced by "quantum" in the description of this particular electronic process. The conceptual model presented here explains the known phenomena without producing paradoxes and unifies quantum and classical electromagnetics.
This chapter discusses electromagnetic waves and photons. It begins by reviewing some basic ideas on the properties of waves, introducing the wave properties of radiation. There are several reasons for starting with a discussion of electromagnetic radiation. Historically, it was in this area that the quantum theory first developed. The applications of the light-quantum hypothesis, as it was first called, also provide key pieces of evidence for the quantization of energy in atoms and molecules. The chapter then looks at the evidence for the wave nature of light and of X-rays, before putting these two forms of radiation into the context of electromagnetic radiation in general. It also considers Albert Einstein's analysis of the photoelectric effect. Finally, the chapter assesses the statistical nature of photons.
This chapter introduces fundamental concepts of modern physics that emerged from groundbreaking experiments and theories in the early 20th century. It begins by exploring the photoelectric effect, which demonstrates the particle nature of light (photons) and provides a basis for mathematical analysis of this phenomenon. The chapter then discusses Bragg diffraction and the concept of the wave function, illustrating the wave nature of particles such as electrons, protons, and neutrons, and introducing the idea of wave-particle duality. The probability distribution for an electron, whether trapped in a well or traveling freely, is also examined. Rutherford scattering is presented as a pivotal experiment that revealed the existence of the positively charged atomic nucleus. The chapter further explores atomic spectra, explaining how the discrete wavelengths of emitted light indicate that atomic electrons have restricted, quantized energy levels. The Bohr model of the atom is described and mathematically analyzed to predict the spectrum of hydrogen. Finally, the chapter covers the Balmer-Rydberg formula for mathematically analyzing the spectrum of hydrogen. The content is organized into sections covering the photoelectric effect, Bragg diffraction and the wave function, Rutherford scattering, atomic spectra, and a summary of the key concepts. This chapter provides an introduction to the revolutionary ideas of modern physics, including the dual nature of light and matter and the quantized nature of the atom. The chapter includes numerous worked examples and concludes with problems for the student to apply their knowledge.