What are photons | Photon Definitions
The term photon is derived from Greek and was first introduced by Gilbert Lewis in 1926. The photon is denoted by the Greek letter and is associated with any electromagnetic radiation. Despite being a wave phenomenon, electromagnetic radiation also has a quantitative nature that allows it to be described as a flow of photons.
A photon is a particle that has infinite life: it can be created and destroyed by interacting with other particles, but it cannot decay spontaneously. Although it has no mass, it is affected by gravity and has energy; In vacuum it travels at the speed of light (c = 300000 km/s approx), whereas in matter it behaves differently and can go below c. Indeed, when it interacts with other particles it gains mass and does not move at the speed of light. Bohr hypothesized that an atom can emit an electromagnetic wave (or radiation) only when an electron moves from an orbit of higher energy (Ei) to an orbit of lower energy (Ef).
The electromagnetic wave energy emitted is: E = Ei-Ef. Since both Ei and Ef can only assume well-defined values, the energy of electromagnetic radiation emitted by an atom can have no value, but only a discrete quantity, called a quanta of energy. Is: Photon. So matter is capable of emitting or absorbing radiation energy only in the form of energy packets. Einstein calculated the energy associated with each photon and observed that it was proportional to the frequency of the electromagnetic wave.
Wave or particle? dual nature of photon
Before the discoveries of the first half of the 20th century, waves and particles seemed to be opposite concepts: a wave filled a region of space, whereas an electron or ion had a well-defined space. At the atomic scale, in fact, the distinction becomes confusing: waves have some properties of particles and vice versa.
Indeed, the photon shows a dual nature, both a particle and a wave: depending on the instrument used to detect it, it behaves like a particle, or it behaves like a wave. The photoelectric effect experiment (a phenomenon in which electrons are emitted by a body affected by electromagnetic waves) suggests a particle nature of light, while diffraction and interference phenomena suggest a wave nature.
To evaluate how light passes through a telescope, its speed is calculated as if the light were a wave. However, when the same wave gives its energy to the atom, it turns out that it behaves like a particle. Whether a beam of light is bright or light, its energy is transmitted in quantities the size of an atom (photon), the energy of which depends only on its wavelength. Observations showed that this wave-particle “duality” also exists in the opposite direction.
An electron must, at all times, have well-defined position and velocity; But quantum physics tells us that precision cannot be achieved in such observations, and suggests that motion can be described as a wave. Wave–particle dualism was considered a paradox until the full introduction of quantum mechanics, in which the two aspects were described in a unified way. Radiation behaves like a wave when it propagates in space, whereas it behaves like a particle when it interacts with matter.
So new quantities and notations are introduced: an electromagnetic wave of wavelength c travels a distance of meters per second. Its frequency, that is, the number of up and down oscillations per second, can be obtained by dividing c by the wavelength: = c/. A fundamental law of quantum physics states that a photon of frequency E has energy E: E = Hν, where H = 6.624 is the 10-34 Joule-second “Planck constant”.
Solid Light and Quantum Computers
Much is known today: Researchers at Princeton University have managed to slow down photons and create a very strange and new form of light: solid light! That is, they made crystals of photons, not atoms, that is, the particles that make up light (frozen photons).
They obtained a cluster of 100 billion atoms of superconducting material as if it were an artificial atom; In its vicinity he passed a superconducting wire containing photons. Light was thus able to “solidify”, changing its nature with a process that has been compared to a phase transition, that is, when a gas is equated to become a liquid or a solid.
The researchers’ ultimate aim is the realization of a quantum computer capable of performing more complex calculations than conventional computers. Who knows, maybe in a few years another young Dreamer Fr.
Will actually ride a solid crystal of light and make the little “big” Einstein’s dream come true!
Second example
The photon is a fundamental particle, which is a quantum of the electromagnetic field. Electromagnetic radiation is emitted and absorbed in the form of photons. Photons have the properties of both a particle and a wave. It has no electric charge or mass. A photon has a fixed energy E = hν (h is the Planck constant, equal to 4.14 10-15 eV in zero).
Along with real photons, there are also so-called virtual photons. The actual photons described above carry the energy of electromagnetic radiation and, depending on this energy, appear in the form of radio waves, ordinary light, X-rays and gamma quanta. Virtual photons are carriers of electromagnetic interaction. For virtual photons the relation between energy and momentum p = E/c is not satisfied. So the virtual photon can have mass and even be at rest. The uncertainty relations of quantum mechanics allow the short-lived appearance of virtual particles.
The electromagnetic interaction between two charged particles is carried out by the exchange of one or more virtual photons. In the role of a carrier of electromagnetic interaction, a photon belongs to the class of so-called gauge bosons – carriers of the fundamental forces of nature.
The photon is a fundamental
A photon is one of the elementary particles, and is the name given when light (electromagnetic wave) is treated as a particle in quantum field theory.
Photons belong to the Bose particles among the elementary particles classified into fermions and Bose particles, and are also one of the 17 elementary particles included in the Standard Model.
As the wavelength of light decreases, the particle nature of light becomes stronger. For example, the Compton effect (also known as Compton scattering) which explains the particle nature of light was performed by X-rays.
Quantum mechanics shows that “light is a particle and a wave”, and that light with a frequency of behaves as a discrete quantum with an energy of the product (Hν) of Planck’s constant h and . The quantum was named a photon. The charge and mass of the photon are both 0, the momentum hν/c (c is the light velocity) in the photon propagation direction, the spin is 1, and the symbol can be represented by the gamma ray followed by .
- Since ancient times, there has been a wave theory in which the matter of light is a “wave” and a particle theory in which the matter of light is a “grain”, and interference experiments have often explained the wave theory. However, in 1900, Planck proposed that light had both “wave” and “particle” properties at the same time, and in 1905, Einstein introduced the concept of a photon (photon) to absorb light. The phenomenon of emission of electrons (photoelectric effect) was explained. Einstein was awarded the Nobel Prize in Physics in 1921 for this theory of the photoelectric effect.
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