Physics
Energy of a Photon
The energy of a photon refers to the amount of energy carried by a single photon, which is a quantum of electromagnetic radiation. It is directly proportional to the frequency of the photon, as described by the equation E=hf, where E is the energy, h is Planck's constant, and f is the frequency. This concept is fundamental in understanding the behavior of light and other forms of electromagnetic radiation.
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9 Key excerpts on "Energy of a Photon"
eBook - ePubFrom Atoms to Higgs Bosons
Voyages in Quasi-Spacetime
- Chary Rangacharyulu, Christopher J. A. Polachic, Chary Rangacharyulu, Christopher J. A. Polachic(Authors)
- 2019(Publication Date)
- Jenny Stanford Publishing(Publisher)
9 but in which no explanation is forthcoming for its emission and absorption in matter.The concept of the photon, as a discrete energy entity or packet of light, is not very different from that of Isaac Newton, who imagined light to be made up of corpuscular bullets. But in classical Newtonian thinking, there was no association between the frequency of light and its energy. In the quantum concept, this is a chief characteristic of light: the Energy of a Photon isE = h v (9.2)as originally given by Planck, where h is a constant of Nature. The frequency parameter for light (v ) is a continuous variable, and so is the energy that a photon may have.9.3 Waves and Particles, Real and Virtual
Until very recently, photons occupied a unique status in particle physics. A “free” photon has zero mass, which makes the energy and momentum numerically the same value. We would recognize this as a kinetic momentum . Another kind of momentum, the canonical momentum , is defined for a photon that is not free, but present within a material medium. As photons propagate in media, they may exert a push or pull on the material, which can be modeled as an effective mass for the photon. In this context, the canonical momentum is sensitive to the electromagnetic properties of the medium in which the photon is moving.Maxwell’s theory of electromagnetism, combined with the spacetime concepts of Einstein’s relativity as a basic premise, yields a body of theory called electrodynamics . Early developments in quantum theory incorporated photons as waves, with quantum mechanical representations for the material bodies with which photons might interact. Photon-matter scattering was described very well by the Klein–Nishina formula , which treats photons as monochromatic waves of well-defined energy. Following the development of quantum electrodynamics (QED), theorists checked that new theory to see if it agreed with the successful Klein–Nishina formula, although the concept of radiation is ontologically very different in the two frameworks. In QED, matter particles and photons do not move in space. Rather, when a photon’s position changes from point A to point B, we mathematically destroy one photon at point A and create another at point B.10 This QED process does not obey the principle of causality and leaves the physical system in an energetically unphysical state for a short time interval—an acceptable situation if we invoke Heisenberg’s uncertainty relations. An example of this kind of scenario is the well-known Compton scattering
- David Halliday, Jearl Walker, Patrick Keleher, Paul Lasky, John Long, Judith Dawes, Julius Orwa, Ajay Mahato, Peter Huf, Warren Stannard, Amanda Edgar, Liam Lyons, Dipesh Bhattarai(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
CHAPTER 38 Photons and matter waves 38.1 The photon, the quantum of light LEARNING OBJECTIVES After reading this module, you should be able to: 38.1.1 explain the absorption and emission of light in terms of quantised energy and photons 38.1.2 for photon absorption and emission, apply the relationships between energy, power, intensity, rate of photons, the Planck constant, the associated frequency, and the associated wavelength. KEY IDEAS • An electromagnetic wave (light) is quantised (allowed only in certain quantities), and the quanta are called photons. • For light of frequency f and wavelength , the photon energy is E = hf, where h is the Planck constant. Why study physics? Understanding radiation and how it interacts with matter helps us to understand more than just how the world works. We can explain why we feel heat from a flame, and we can capture images of bones using x-rays to identify diseases. By exploring how radiation interacts with matter, scientist have been able to develop new ways of treating diseases and have made advancements in modern medicine, such as developing new techniques to cure cancer. The photon, the quantum of light Quantum physics (which is also known as quantum mechanics and quantum theory) is largely the study of the microscopic world. In that world, many quantities are found only in certain minimum (elementary) amounts, or integer multiples of those elementary amounts; these quantities are then said to be quantised. The elementary amount that is associated with such a quantity is called the quantum of that quantity (quanta is the plural). In a loose sense, US currency is quantised because the coin of least value is the penny, or $0.01 coin, and the values of all other coins and bills are restricted to integer multiples of that least amount. In other words, the currency quantum is $0.01, and all greater amounts of currency are of the form n($0.01), where n is always a positive integer.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Library Press(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter- 1 Photon Photon Photons emitted in a coherent beam from a laser Composition: Elementary particle Particle statistics: Bosonic Group: Gauge boson Interaction: Electromagnetic Symbol(s): γ, hν, or ħω Theorized: Albert Einstein Mass: 0 <1×10 −18 eV Mean lifetime: Stable Electric charge: 0 <1×10 −35 e Spin: 1 Parity: -1 C parity: -1 Condensed: I ( J PC ) = 0,1(1 --) ________________________ WORLD TECHNOLOGIES ________________________ In physics , a photon is an elementary particle , the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force. The effects of this force are easily observable at both the microscopic and macroscopic level, be cause the photon has no rest mass; this allows for interactions at long distances. Like all elementary particles, photons are currently best explained by quantum mechanics and will exhibit wave–particle duality — they exhibit properties of both waves and particles . For example, a single photon may be refracted by a lens or exhibit wave interference with itself, but also act as a particle giving a definite result when quantitative momentum is measured. The modern concept of the photon was developed gradually by Albert Einstein to explain experimental observations that did not fit the classical wave model of light. In particular, the photon model accounted for the frequency dependence of light's energy, and explained the ability of matter and radiation to be in thermal equilibrium. It also accounted for anomalous observations, including the properties of black body radiation , that other physicists, most notably Max Planck , had sought to explain using semiclassical models , in which light is still described by Maxwell's equations , but the material objects that emit and absorb light are quantized.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Orange Apple(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter- 9 Photon Photon Photons emitted in a coherent beam from a laser Composition: Elementary particle Particle statistics: Bosonic Group: Gauge boson Interaction: Electromagnetic Symbol(s): γ, hν, or ħω Theorized: Albert Einstein Mass: 0<1×10 −18 eV Mean lifetime: Stable Electric charge: 0<1×10 −35 e Spin: 1 Parity: -1 C parity: -1 Condensed: I ( J PC ) = 0,1(1 --) In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. In other words a photon is a little packet of energy which can carry electromagnetic radiation. It is also the force carrier for the electromagnetic force. The effects of this force are easily observable at both the microscopic and macroscopic level, because the photon ________________________ WORLD TECHNOLOGIES ________________________ has no rest mass; this allows for interactions at long distances. Like all elementary particles, photons are currently best explained by quantum mechanics and will exhibit wave–particle duality, exhibiting properties of both waves and particles. For example, a single photon may be refracted by a lens or exhibit wave interference with itself, but also act as a particle giving a definite result when quantitative momentum is measured. The modern concept of the photon was developed gradually by Albert Einstein to explain experimental observations that did not fit the classical wave model of light. In particular, the photon model accounted for the frequency dependence of light's energy, and explained the ability of matter and radiation to be in thermal equilibrium.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- College Publishing House(Publisher)
____________________ WORLD TECHNOLOGIES ____________________ Chapter 5 Photon Photon Photons emitted in a coherent beam from a laser Composition: Elementary particle Particle statistics: Bosonic Group: Gauge boson Interaction: Electromagnetic Symbol(s): γ, hν, or ħω Theorized: Albert Einstein Mass: 0 <1×10 −18 eV Mean lifetime: Stable Electric charge: 0 <1×10 −35 e Spin: 1 Parity: -1 C parity: -1 Condensed: I ( J PC ) = 0,1(1 --) In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force. The effects of this force are easily observable at both the microscopic and macroscopic level, because the photon has no rest mass; this allows for interactions at long distances. Like all elementary particles, photons ____________________ WORLD TECHNOLOGIES ____________________ are currently best explained by quantum mechanics and will exhibit wave–particle duality — they exhibit properties of both waves and particles. For example, a single photon may be refracted by a lens or exhibit wave interference with itself, but also act as a particle giving a definite result when quantitative momentum is measured. The modern concept of the photon was developed gradually by Albert Einstein to explain experimental observations that did not fit the classical wave model of light. In particular, the photon model accounted for the frequency dependence of light's energy, and explained the ability of matter and radiation to be in thermal equilibrium. It also accounted for anomalous observations, including the properties of black body radiation, that other physicists, most notably Max Planck, had sought to explain using semiclassical models , in which light is still described by Maxwell's equations, but the material objects that emit and absorb light are quantized.
eBook - PDF- David Halliday, Robert Resnick, Jearl Walker(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
1225 C H A P T E R 3 8 Photons and Matter Waves 38.1 THE PHOTON, THE QUANTUM OF LIGHT Learning Objectives After reading this module, you should be able to . . . 38.1.1 Explain the absorption and emission of light in terms of quantized energy and photons. 38.1.2 For photon absorption and emission, apply the relationships between energy, power, intensity, rate of photons, the Planck constant, the associated frequency, and the associated wavelength. Key Ideas ● An electromagnetic wave (light) is quantized (allowed only in certain quantities), and the quanta are called photons. ● For light of frequency f and wavelength λ, the photon energy is E = hf, where h is the Planck constant. What Is Physics? One primary focus of physics is Einstein’s theory of relativity, which took us into a world far beyond that of ordinary experience—the world of objects moving at speeds close to the speed of light. Among other surprises, Einstein’s theory predicts that the rate at which a clock runs depends on how fast the clock is moving relative to the observer: the faster the motion, the slower the clock rate. This and other predictions of the theory have passed every experimental test devised thus far, and relativity the- ory has led us to a deeper and more satisfying view of the nature of space and time. Now you are about to explore a second world that is outside ordinary experience—the subatomic world. You will encounter a new set of surprises that, though they may sometimes seem bizarre, have led physicists step by step to a deeper view of reality.
- David Halliday, Robert Resnick, Jearl Walker(Authors)
- 2023(Publication Date)
- Wiley(Publisher)
Indeed, it is still very poorly understood. In this book, we shall discuss only some of the basic aspects of the photon concept, somewhat along the lines of Einstein’s proposal. According to that proposal, the quantum of a light wave of frequency f has the energy E = hf (photon energy). (38.1.2) Here h is the Planck constant, the constant we first met in Eq. 32.5.2, and which has the value h = 6.63 × 10 −34 J · s = 4.14 × 10 −15 eV ⋅ s. (38.1.3) The smallest amount of energy a light wave of frequency f can have is hf , the energy of a single photon. If the wave has more energy, its total energy must be an integer multiple of hf. The light cannot have an energy of, say, 0.6hf or 75.5hf. Einstein further proposed that when light is absorbed or emitted by an object (matter), the absorption or emission event occurs in the atoms of the object. When light of frequency f is absorbed by an atom, the energy hf of one photon is trans- ferred from the light to the atom. In this absorption event, the photon vanishes and the atom is said to absorb it. When light of frequency f is emitted by an atom, an amount of energy hf is transferred from the atom to the light. In this emission event, a photon suddenly appears and the atom is said to emit it. Thus, we can have photon absorption and photon emission by atoms in an object. For an object consisting of many atoms, there can be many photon absorp- tions (such as with sunglasses) or photon emissions (such as with lamps). How- ever, each absorption or emission event still involves the transfer of an amount of energy equal to that of a single photon of the light. When we discussed the absorption or emission of light in previous chapters, our examples involved so much light that we had no need of quantum physics, and we got by with classical physics. However, in the late 20th century, tech- nology became advanced enough that single-photon experiments could be con- ducted and put to practical use.
eBook - PDF- Peter Hedvig(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
The most general view is to regard the radiation field as quantized and consider the interaction of two quantized fields: the field of electron bound in the atom or molecule and that of the electromagnetic radiation. Fortunately the basic phenomena interesting in chemistry can be fairly well interpreted by the semiclassical approach. Only recently has been dis-covered such a field where the more complex quantum field theory is ab-solutely necessary to understand the experimental facts; this is the inter-action of high intensity laser light with matter [2.19]. When photons interact with atoms or molecules changes in the properties of photons and in those of the atoms or molecules are observed. The main changes suffered by the photons are the following. 1. Absorption not accompanied by re-emission of radiation. The photon energy in these cases is transformed into the kinetical energy of particles (photoelectric effect, Compton effect) or into heat. 2. Rayleigh scattering, when the energy of the scattered photons, is the same as the incident one. The consequences of Rayleigh scattering are: reflection, refraction, diffraction, rotation of the plane of polarization and depolarization. 3. Phosphorescence and fluorescence: re-emission of photons after absorp-tion in a long (10 -4 sec) and a short (10~ 8 sec) time interval, respectively. The energy of the re-emitted photons is usually smaller (the wavelength longer) than that of the incident ones. 4. Raman scattering, when the energy of the scattered photons is slightly different from the incident one (cf. Chapter 6). 5. Compton effect, when the energy of the scattered photons is much smal-ler (the wavelength longer) than the incident one; a part of the photon energy is transferred to the particle (electron) by elastic collision (cf. Chapter 1). INTERACTION OF RADIATION 71 6. Electron-positron pair formation. In this process the high energy gamma photons form electron-positron pairs near heavy nuclei.
eBook - PDFMolecular Photonics
Fundamentals and Practical Aspects
- Kazuyuki Horie, Hideharu Ushiki, Françoise M. Winnik, Kazuyuki Horie, Hideharu Ushiki, Françoise M. Winnik(Authors)
- 2008(Publication Date)
- Wiley-VCH(Publisher)
Hence the maximum energy to eject an electron is EMAX = hv - W = h(v - vo). The remarkable contribution to science by Einstein’s explanation of the photoelectric effect can be focused on the following facts. ( I ) The concept of quantized energy applies to phenomena related to the emission of light as well as to the absorption of light. In this, it will serve in the interpretation of the hydrogen emission spectrum, leading Bohr to formulate his description of the hydrogen atom, the third phase in the formation of quantum theory. (2) The concept of quantized energy can be pursued further to describe the motion of energy in free space as a localized wave packet. Therefore it is at the origin of quantum electrodynamics. The wave theory of light reached its climax with Hertz’s contributions around 1888. Physics was now in a state of turmoil, torn apart by the wave-particle duality caused by the quantum theory. As a result, research in photo- and opto-related areas was divided into two streams: quantum electrodynamics and molecular spectroscopy. There is no question that the three reports, “the photoelectric effect,” “the special relativity” and “the Brownian motion” published by Einstein in 1905 changed the traditional consciousness of researchers in the 20th century. The report on the “photoelectric effect” clarified an old problem in the wave theory of light by linking discussions on the nature of light and the quantum hypothesis originating in Planck’s study of specific heat. The report on “special relativity” refuted the ether theory and created an entirely new field. The report on “Brownian motion,” aimed at the very existence of atoms and molecules, created the theory 1.2 The Moleculdr Field Theory 25 of the stochastic process as a new field of study. These three reports cannot be separated. In the formative period of quantum mechanics, the concepts of existence, understandability, and causality had become key issues for physicists.
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