It consists of two parts: macroscopic electron theory, based on Maxwell’s equations, and classical electron theory.
The basic equations of classical electrodynamics are Maxwell's equations, which establish a connection between the quantities characterizing electric and magnetic fields with the distribution of charges and currents in space. The essence of Maxwell's four equations for the electromagnetic field is qualitatively reduced to the following:
1. The magnetic field is generated by moving charges and an alternating electric field;
2. An electric field with closed lines of force (vortex field) is generated by an alternating magnetic field;
3. The magnetic field lines are always closed (this means that it has no sources - magnetic charges similar to electric ones);
4. An electric field with unlocked lines of force (potential field) is generated by electric charges - the sources of this field. Maxwell's theory implies the finiteness of the speed of propagation of electromagnetic interactions and the existence of electromagnetic waves.
Classical electrodynamics also considers electromagnetic waves, their radiation and propagation in space.
A separate section of classical electrodynamics is the electrodynamics of continuous media, which considers the response of physical media to disturbances by external electric and magnetic fields.
§ 1. Coulomb's law
§ 2. Tension electric field
§ 3. Gauss's theorem
§ 4. Differential form of Gauss's theorem
§ 5. The second equation of electrostatics and scalar potential
§ 6. Surface distributions of charges and dipoles. Electric field and potential jumps
§ 7. Laplace and Poisson equations
§ 8. Green's theorem
§ 9. Uniqueness of the solution under Dirichlet or Neumann boundary conditions
§ 10. Formal solution of boundary value problems of electrostatics using the Green's function
§ 11. Potential energy and energy density of the electrostatic field
Recommended reading
Tasks
§ 1. Method of images
§ 2. Point charge near a grounded spherical conductor
§ 3. Point charge near a charged insulated spherical conductor
§ 4. Point charge near a spherical conductor with a given potential
§ 5. Spherical conductor in a homogeneous electric field
§ 6. Inversion method
§ 7. Green's function for a sphere. General expression for potential
§ 8. Two adjacent conducting hemispheres having different potentials
§ 9. Expansion in orthogonal functions
§ 10. Separation of variables. Laplace's equation in Cartesian coordinates
Recommended reading
Tasks
§ 1. Laplace's equation in spherical coordinates
§ 2. Legendre's equation and Legendre's polynomials
§ 3. Boundary value problems with azimuthal symmetry
§ 4. Associated Legendre functions and spherical harmonics
§ 5. Addition theorem for spherical harmonics
§ 6. Laplace's equation in cylindrical coordinates. Bessel functions
§ 7. Boundary value problems in cylindrical coordinates
§ 8. Expansion of Green's functions in spherical coordinates
§ 9. Finding the potential using expansions for spherical Green's functions
§ 10. Expansion of Green's functions in cylindrical coordinates
§ 11. Expansion of Green's functions in terms of eigenfunctions
§ 12. Mixed boundary conditions. Charged conductive disk
Recommended reading
Tasks
§ 1. Multipole expansion
§ 2. Expansion into multipoles of the energy distribution of charges in external field
§ 3. Macroscopic electrostatics. Effects of the combined action of atoms
§ 4. Isotropic dielectrics and boundary conditions
§ 5. Boundary value problems in the presence of dielectrics
§ 6. Polarizability of molecules and dielectric susceptibility
§ 7. Models of molecular polarizability
§ 8. Electric field energy in a dielectric
Recommended reading
Tasks
§ 1. Introduction and basic definitions
§ 2. Law of Biot and Savart
§ 3. Differential equations magnetostatics and Ampere's law
§ 4. Vector potential
§ 5. Vector potential and magnetic induction of a circular current loop
§ 6. Magnetic field of limited current distribution. Magnetic moment
§ 7. Force and torque acting on a limited current distribution in an external magnetic field
§ 8. Macroscopic equations
§ 9. Boundary conditions for magnetic induction and field
§ 10. Uniformly magnetized ball
§ 11. Magnetized ball in an external field. Permanent magnets
§ 12. Magnetic shielding. Spherical shell of magnetic material in a uniform field
Recommended reading
Tasks
§ 1. Faraday's law of induction
§ 2. Magnetic field energy
§ 3. Maxwellian displacement current. Maxwell's equations
§ 4. Vector and scalar potentials
§ 5. Gauge transformations. Lorentz gauge. Coulomb gauge
§ 6. Green's function for the wave equation
§ 7. Problem with initial conditions. Kirchhoff integral representation
§ 8. Poynting's theorem
§ 9. Conservation laws for a system of charged particles and electromagnetic fields
§ 10. Macroscopic equations
Recommended reading
Tasks
§ 1. Plane waves in a non-conducting medium
§ 2. Linear and circular polarization
§ 3. Superposition of waves in one dimension. Group speed
§ 4. Examples of pulse propagation in a dispersive medium
§ 5. Reflection and refraction of electromagnetic waves at a flat interface between dielectrics
§ 6. Polarization during reflection and total internal reflection
§ 7. Waves in a conducting medium
§ 8. Simple model conductivity
§ 9. Transverse waves in rarefied plasma
Recommended reading
Tasks
§ 1. Fields on the surface and inside a conductor
§ 2. Cylindrical resonators and waveguides
§ 3. Waveguides
§ 4. Waves in a rectangular waveguide
§ 5. Energy flow and attenuation in waveguides
§ 6. Resonators
§ 7. Power losses in the resonator. Resonator quality factor
§ 8. Dielectric waveguides
Recommended reading
Tasks
§ 1. Fields created by limited oscillating sources
§ 2. Electric dipole field and radiation
§ 3. Magnetic dipole and electric quadrupole fields
§ 4. Linear antenna with central excitation
§ 5. Kirchhoff integral
§ 6. Vector equivalents of the Kirchhoff integral
§ 7. Babinet's principle for additional screens
§ 8. Diffraction by round hole
§ 9. Diffraction by small holes
§ 10. Scattering of short waves by a conducting sphere
Recommended reading
Tasks
§ 1. Introduction and basic concepts
§ 2. Equations of magnetohydrodynamics
§ 3. Magnetic diffusion, viscosity and pressure
§ 4. Magnetohydrodynamic flow between boundaries in crossed electric and magnetic fields
§ 5. Pinch effect
§ 6. Dynamic model of the pinch effect
§ 7. Instabilities of a compressed plasma column
§ 8. Magnetohydrodynamic waves
§ 9. High-frequency plasma oscillations
§ 10. Short-wave plasma oscillations. Debye screening radius
Recommended reading
Tasks
§ 1. Historical background and main experiments
§ 2. Postulates special theory relativity and Lorentz transformation
§ 3. Fitzgerald-Lorentz contraction and time dilation
§ 4. Addition of velocities. Aberration and Fizeau's experience. Doppler shift
§ 5. Thomas Precession
§ 6. Own time and light cone
§ 7. Lorentz transformations as orthogonal transformations in four-dimensional space
§ 8. Four vectors and four tensors. Covariance of physics equations
§ 9. Covariance of electrodynamic equations
§ 10. Transformation of the electromagnetic field
§ 11. Covariance of the expression for the Lorentz force and conservation laws
Recommended reading
Tasks
§ 1. Momentum and energy of a particle
§ 2. Kinematics of fragments during the decay of an unstable particle
§ 3. Conversion to the center of mass system and reaction thresholds
§ 4. Conversion of momentum and energy from the center of mass system to the laboratory system
§ 5. Covariant equations of motion. Lagrangian and Hamiltonian for a relativistic charged particle
§ 6. First-order relativistic corrections for the Lagrangians of interacting charged particles
§ 7. Motion in a uniform static magnetic field
§ 8. Motion in uniform static electric and magnetic fields
§ 9. Particle drift in a non-uniform static magnetic field
§ 10. Adiabatic invariance of magnetic flux through the orbit of a particle
Recommended reading
Tasks
§ 1. Energy transfer during Coulomb collisions
§ 2. Transfer of energy to a harmonic oscillator
§ 3. Classical and quantum mechanical expression for energy losses
§ 4. Influence of density on energy loss during collision
§ 5. Energy losses in electron plasma
§ 6. Elastic scattering of fast particles by atoms
§ 7. Root mean square value of the scattering angle and angular distribution for multiple scattering
§ 8. Electrical conductivity of plasma
Recommended reading
Tasks
§ 1. Lienard-Wiechert potentials and the field of a point charge
§ 2. Total power emitted by an accelerated moving charge. Larmore's formula and its relativistic generalization
§ 3. Angular distribution of radiation from an accelerated charge
§ 4. Charge emission during arbitrary ultrarelativistic motion
§ 5. Spectral and angular distributions of energy emitted by accelerated charges
§ 6. Radiation spectrum of a relativistic charged particle during instantaneous motion in a circle
§ 7. Scattering by free charges. Thomson's formula
§ 8. Coherent and incoherent scattering
§ 9. Vavilov-Cherenkov radiation
Recommended reading
Tasks
§ 1. Radiation during collisions
§ 2. Bremsstrahlung during nonrelativistic Coulomb collisions
§ 3. Bremsstrahlung during relativistic motion
§ 4. Effect of shielding. Radiation losses in the relativistic case
§ 5. Weizsäcker-Williams virtual photon method
§ 6. Bremsstrahlung as scattering of virtual photons
§ 7. Radiation from beta decay
§ 8. Radiation during the capture of orbital electrons. Disappearance of charge and magnetic moment
Recommended reading
Tasks
§ 1. Eigenfunctions of the scalar wave equation
§ 2. Expansion of electromagnetic fields into multipoles
§ 3. Properties of multipole fields. Energy and angular momentum of multipole radiation
§ 4. Angular distribution of multipole radiation
§ 5. Sources of multipole radiation. Multipole moments
§ 6. Multipole radiation of atomic and nuclear systems
§ 7. Radiation of a linear antenna with central excitation
§ 8. Expansion of a vector plane wave in spherical waves
§ 9. Scattering of electromagnetic waves on a conducting sphere
§ 10. Solving boundary value problems using multipole expansions
Recommended reading
Tasks
§ 1. Introductory remarks
§ 2. Determination of the radiation reaction force from the law of conservation of energy
§ 3. Calculation of the radiation reaction force according to Abraham and Lorentz
§ 4. Difficulties of the Abraham-Lorentz model
§ 5. Transformation properties of the Abraham-Lorentz model. Poincaré tensions
§ 6. Covariant determination of the intrinsic electromagnetic energy and momentum of a charged particle
§ 7. Integro-differential equation of motion taking into account radiative attenuation
§ 8. Line width and level shift for the oscillator
§ 9. Scattering and absorption of radiation by an oscillator
Recommended reading
Tasks
§ 1. Units of measurement and dimensions. Basic and derived units
§ 2. Units of measurement and equations of electrodynamics
§ 3. Various systems electromagnetic units
§ 4. Translation of formulas and numerical values quantities from the Gaussian system of units to the ISS system
Definition 1
Electrodynamics is a theory that examines electromagnetic processes in a vacuum and various media.
Electrodynamics covers a set of processes and phenomena in which the key role is played by the actions between charged particles, which are carried out through an electromagnetic field.
History of the development of electrodynamics
The history of the development of electrodynamics is the history of the evolution of traditional physical concepts. Even before the mid-18th century, important experimental results were established that were due to electricity:
- repulsion and attraction;
- dividing matter into insulators and conductors;
- existence of two types of electricity.
Considerable results have also been achieved in the study of magnetism. The use of electricity began in the second half of the 18th century. The emergence of the hypothesis about electricity as a special material substance is associated with the name of Franklin (1706-1790). And in 1785, Coulomb established the law of interaction of point charges.
Volt (1745-1827) invented many electrical measuring instruments. In 1820, a law was established that determined mechanical force, with which the magnetic field acts on the element electric current. This phenomenon became known as Ampere's law. Ampere also established the law of the force action of several currents. In 1820, Oersted discovered the magnetic effect of electric current. Ohm's law was established in 1826.
In physics, the hypothesis of molecular currents, which was proposed by Ampere back in 1820, is of particular importance. Faraday discovered the law of electromagnetic induction in 1831. James Clerk Maxwell (1831-1879) in 1873 set out the equations that later became the theoretical basis of electrodynamics. A consequence of Maxwell's equations is the prediction of the electromagnetic nature of light. He also predicted the possibility of the existence of electromagnetic waves.
Over time, physical science developed the idea of the electromagnetic field as an independent material entity, which is a kind of carrier of electromagnetic interactions in space. Various magnetic and electrical phenomena have always aroused people's interest.
Often the term “electrodynamics” refers to traditional electrodynamics, which describes only the continuous properties of the electromagnetic field.
The electromagnetic field is the main subject of study of electrodynamics, as well as special kind matter, which manifests itself when interacting with charged particles.
Popov A.S. In 1895 he invented radio. It was this that had a key impact on the further development of technology and science. Maxwell's equations can be used to describe all electromagnetic phenomena. The equations establish the relationship between quantities that characterize magnetic and electric fields, distributing currents and charges in space.
Figure 1. Development of the doctrine of electricity. Author24 - online exchange of student works
Formation and development of traditional electrodynamics
The key and most significant step in the development of electrodynamics was the discovery of Faraday - the phenomenon of electromagnetic induction (excitation of electromotive force in conductors using an alternating electromagnetic field). This is what became the basis of electrical engineering.
Michael Faraday is an English physicist who was born into the family of a blacksmith in London. He graduated primary school and from the age of 12 he worked as a newspaper delivery boy. In 1804, he became a student of the French emigrant Ribot, who encouraged Faraday's desire for self-education. At lectures, he sought to expand his knowledge of the natural sciences of chemistry and physics. In 1813 he was given a ticket to Humphry Davy's lectures, which played decisive role in his destiny. With his help, Faraday received a position as an assistant at the Royal Institution.
Faraday's scientific work took place at the Royal Institution, where he first helped Davy in his chemical experiments, after which he began to carry them out on his own. Faraday obtained benzene by reducing chlorine and other gases. In 1821, he discovered how a magnet rotates around a current-carrying conductor, creating the first model of an electric motor.
Over the next 10 years, Faraday studied the connections between magnetic and electrical phenomena. All his research was crowned with the discovery of the phenomenon of electromagnetic induction, which happened in 1831. He studied this phenomenon in detail, and also formed its basic law, during which he revealed the dependence of the induction current. Faraday also investigated the phenomena of closure, opening and self-induction.
The discovery of electromagnetic induction produced scientific significance. This phenomenon underlies all alternating and direct current. Since Faraday constantly sought to identify the nature of electric current, this led him to conduct experiments on the passage of current through solutions of salts, acids and alkalis. As a result of these studies, the law of electrolysis appeared, which was discovered in 1833. This year he opens a voltmeter. In 1845, Faraday discovered the phenomenon of polarization of light in a magnetic field. This year he also discovered diamagnetism, and in 1847 paramagnetism.
Note 1
Faraday's ideas about magnetic and electric fields had a key influence on the development of all physics. In 1832, he proposed that the propagation of electromagnetic phenomena is a wave process that occurs at a finite speed. In 1845, Faraday first used the term “electromagnetic field.”
Faraday's discoveries gained wide popularity throughout the scientific world. In his honor, the British Chemical Society established the Faraday Medal, which became an honorary scientific award.
Explaining the phenomena of electromagnetic induction and encountering difficulties, Faraday suggested the implementation of electromagnetic interactions using an electric and magnetic field. This all laid the foundation for the creation of the concept of the electromagnetic field, which was formalized by James Maxwell.
Maxwell's contribution to the development of electrodynamics
James Clerk Maxwell is an English physicist who was born in Edinburgh. It was under his leadership that the Cavendish Laboratory in Cambridge was created, which he headed throughout his life.
Maxwell's works are devoted to electrodynamics, general statistics, molecular physics, mechanics, optics, and the theory of elasticity. He made his most significant contributions to electrodynamics and molecular physics. One of the founders of the kinetic theory of gases is Maxwell. He established the velocity distribution functions of molecules, which are based on the consideration of reverse and direct collisions. Maxwell developed the theory of transfer in a general form and applied it to the processes of diffusion, internal friction, thermal conductivity, and also introduced the concept of relaxation.
In 1867, he first showed the statistical nature of thermodynamics, and in 1878 he introduced the concept of “statistical mechanics”. The most significant scientific achievement Maxwell is the theory of the electromagnetic field he created. In his theory, he uses a new concept “displacement current” and gives a definition of the electromagnetic field.
Note 2
Maxwell predicts an important new effect: the existence electromagnetic radiation and electromagnetic waves in free space, as well as their propagation at the speed of light. He also formulated a theorem in the theory of elasticity, establishing the relationship between key thermophysical parameters. Maxwell develops the theory of color vision and studies the stability of Saturn's rings. It shows that the rings are not liquid or solid, but are a swarm of meteorites.
Maxwell was a famous popularizer physical knowledge. The contents of his four electromagnetic field equations are as follows:
- A magnetic field is generated with the help of moving charges and an alternating electric field.
- An electric field with closed lines of force is generated with the help of an alternating magnetic field.
- Magnetic field lines are always closed. This field does not have magnetic charges, which are similar to electric ones.
- An electric field, which has open lines of force, is generated by electric charges, which are the sources of this field.
The book is a course of lectures on classical electrodynamics, which the author read for many years as an undergraduate Faculty of Physics St. Petersburg (Leningrad) state university. The course is based on fundamental principles such as Maxwell's equations and the principle of relativity, combined in the relativistic covariant form of the electrodynamics equations. On their basis, the basic ideas and methods of electrostatics, radiation theory, electrodynamics of continuous media and the theory of waveguides are consistently presented. The material is presented with a high degree of mathematical rigor, which is seamlessly combined with a clear presentation of the physical content. The book can be useful to anyone who, having basic knowledge in the field of electrical phenomena and mathematical analysis, would like to get a clear and mathematically rigorous understanding of how theoretical foundations, and about methods for solving the most complex tasks electrodynamics.
Fragment from the book.
Summary: when considering radio engineering problems of the type “how does this antenna radiate,” we are, of course, only interested in the field created by it itself, and to exclude external free fields, it is natural to impose the necessary asymptotic conditions at infinity on the potentials. With this formulation, the above gauge conditions fix the potentials uniquely. But if we are interested in the free fields themselves (which is natural when formulating problems, for example, in quantum field theory), then we cannot impose conditions that exclude these very fields.
Preface
1 General introduction
1.1 Maxwell's equations.
1.2 Mathematical digression: notation conventions, reference formulas.
1.3 Integral form of Maxwell's equations.
1.4 The relationship between the differential and integral forms of Maxwell's equations in the presence of discontinuity surfaces. Boundary conditions (matching conditions).
1.5 Continuity equation, charge conservation law.
1.6 Transition from tensions to potentials. Maxwell's equations for potentials.
1.7 Calibration transformations and calibration conditions.
2 Relativistic-covariant formulation of electrodynamics
2.1 Designations.
2.2 Tensors on the SO3 rotation group and on the 03 group.
2.3 Tensor fields.
2.4 Electrodynamics and the principle of relativity.
2.5 Lorentz transformations, general properties.
2.6 Lorentz eigentransformations. Explicit form of transformations of the transition to a moving reference frame..
2.7 Relativistic law of addition of velocities. Reducing scale and stretching time.
2.8 Tensors and tensor fields on the Lorentz group.
2.9 Tensor nature of potentials and tensions.
2.10 Covariant formulation of Maxwell's equations for potentials.
2.11 Transversality K, continuity equation, gauge invariance of Maxwell’s equations, gauge conditions.
2.12 General considerations on the form of Maxwell’s equations for potentials.
2.13 Covariant recording of Maxwell's equations for tensions.
2.14 Transformations of potentials and tensions during the transition to a moving reference frame.
2.15 Electrodynamics from the perspective theoretical mechanics. Action functional for electromagnetic field.
2.16 Energy-momentum tensor. Laws of conservation of energy and momentum.
2.17 Elements of relativistic dynamics of a point particle. Lorentz force.
3 Statics
3.1 Basic relationships.
3.2 Solution of Poisson's equation.
3.3 Multipole expansion of the scalar potential
in electrostatics. Multipole moments and their properties.
3.4 Multifield expansion of the vector potential A in magnetostatics. Magnetic moment of an arbitrary current system.
3.5 Forces and moments of forces. acting on distributed sources.
3.6 Potential energy of a system of charges or currents
in a given external field.
3.7 Own potential energy of a system of charges or currents (energy in its own field).
3.8 Dielectrics and magnets (statics).
3.9 Fundamentals of thermodynamics of dielectrics and magnets. Volume forces in dielectrics and magnets.
3.10 Boundary value problems of electrostatics and methods for their solution....
4 Dynamics
4.1 Statement of the problem, general form solutions.
4.2 Retarded Green's function of the wave operator....
4.3 Delayed potentials.
4.4 Field of an arbitrarily moving point charge. Liénard-Wiechert potentials. Radiation power and radiation pattern.
4.5 Radiation from localized sources, multipole decomposition.
4.6 Linear antenna with central excitation.
4.7 Maxwell's dynamic equations in a medium.
4.8 Waveguides.
Literature Subject index
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Subject of classical electrodynamics
Classical electrodynamics is a theory that explains the behavior of the electromagnetic field that carries out the electromagnetic interaction between electric charges.
The laws of classical macroscopic electrodynamics are formulated in Maxwell’s equations, which make it possible to determine the values of the characteristics of the electromagnetic field: electric field strength E and magnetic induction IN in vacuum and in macroscopic bodies, depending on the distribution of electric charges and currents in space.
The interaction of stationary electric charges is described by the equations of electrostatics, which can be obtained as a consequence of Maxwell's equations.
The microscopic electromagnetic field created by individual charged particles is determined in classical electrodynamics by the Lorentz-Maxwell equations, which underlie the classical statistical theory of electromagnetic processes in macroscopic bodies. Averaging these equations leads to Maxwell's equations.
Among all known species interactions, electromagnetic interaction ranks first in terms of breadth and variety of manifestations. This is due to the fact that all bodies are built from electrically charged (positive and negative) particles, the electromagnetic interaction between which, on the one hand, is many orders of magnitude more intense than gravitational and weak interaction, and on the other hand, is long-range, in contrast to the strong interaction.
Electromagnetic interaction determines the structure of atomic shells, the cohesion of atoms into molecules (forces chemical bond) and the formation of condensed matter (interatomic interaction, intermolecular interaction).
The laws of classical electrodynamics are not applicable at high frequencies and, accordingly, short lengths of electromagnetic waves, i.e. for processes occurring over small space-time intervals. In this case, the laws of quantum electrodynamics are valid.
1.2. Electric charge and its discreteness.
Short-range theory
The development of physics has shown that physical and Chemical properties substances are largely determined by interaction forces caused by the presence and interaction of electrical charges of molecules and atoms of various substances.
It is known that in nature there are two types of electrical charges: positive and negative. They can exist in the form elementary particles: electrons, protons, positrons, positive and negative ions, etc., as well as “free electricity,” but only in the form of electrons. Therefore, a positively charged body is a collection of electric charges with a lack of electrons, and a negatively charged body is an excess of them. Charges of different signs compensate each other, therefore, in uncharged bodies there are always charges of both signs in such quantities that their total effect is compensated.
Redistribution process positive and negative charges of uncharged bodies, or among separate parts of the same body, under the influence various factors called electrification.
Since free electrons are redistributed during electrification, then, for example, both interacting bodies are electrified, one of them being positive and the other negative. The number of charges (positive and negative) remains unchanged.
From here it follows that charges are neither created nor destroyed, but are only redistributed between interacting bodies and parts of the same body, remaining quantitatively unchanged.
This is the meaning of the law of conservation of electric charges, which can be written mathematically as follows:
those. in an isolated system, the algebraic sum of electric charges remains a constant value.
An isolated system is understood as a system through the boundaries of which no other substance penetrates, with the exception of photons of light and neutrons, since they do not carry a charge.
It must be borne in mind that the total electric charge of an isolated system is relativistically invariant, because observers located in any given inertial coordinate system, measuring the charge, obtain the same value.
A number of experiments, in particular the laws of electrolysis, Millikan's experiment with a drop of oil, showed that in nature electric charges are discrete to the charge of an electron. Any charge is an integer multiple of the electron's charge.
During the electrification process, the charge changes discretely (quantized) by the amount of the electron charge. Charge quantization is a universal law of nature.
In electrostatics, the properties and interactions of charges that are stationary in the frame of reference in which they are located are studied.
The presence of an electric charge in bodies causes them to interact with other charged bodies. In this case, similarly charged bodies repel, and oppositely charged bodies attract.
The theory of short-range interaction is one of the theories of interaction in physics. In physics, interaction is understood as any influence of bodies or particles on each other, leading to a change in the state of their motion.
In Newtonian mechanics, the mutual action of bodies on each other is quantitatively characterized by force. More general characteristic interaction is potential energy.
Initially, physics established the idea that interaction between bodies can be carried out directly through empty space, which does not take part in the transmission of interaction. The transfer of interaction occurs instantly. Thus, it was believed that the movement of the Earth should immediately lead to a change in the gravitational force acting on the Moon. This was the meaning of the so-called theory of interaction, called the theory of long-range action. However, these ideas were abandoned as untrue after the discovery and study of the electromagnetic field.
It was proven that the interaction of electrically charged bodies is not instantaneous and the movement of one charged particle leads to a change in the forces acting on other particles, not at the same moment, but only after a finite time.
Each electrically charged particle creates an electromagnetic field that acts on other particles, i.e. interaction is transmitted through an “intermediary” – an electromagnetic field. The speed of propagation of the electromagnetic field is equal to the speed of propagation of light in a vacuum. Arose new theory interaction theory of short-range interaction.
According to this theory, interaction between bodies is carried out through certain fields (for example, gravity through a gravitational field) continuously distributed in space.
After the advent of quantum field theory, the idea of interactions changed significantly.
According to quantum theory, any field is not continuous, but has a discrete structure.
Due to wave-particle duality, each field corresponds to certain particles. Charged particles continuously emit and absorb photons, which form the electromagnetic field surrounding them. Electromagnetic interaction in quantum field theory is the result of the exchange of particles by photons (quanta) of the electromagnetic field, i.e. photons are carriers of such interaction. Similarly, other types of interactions arise as a result of the exchange of particles by quanta of the corresponding fields.
Despite the variety of influences of bodies on each other (depending on the interaction of the elementary particles that compose them), in nature, according to modern data, there are only four types of fundamental interactions: gravitational, weak, electromagnetic and strong (in order of increasing intensity of interaction). The intensities of interactions are determined by coupling constants (in particular, the electric charge for electromagnetic interaction is a coupling constant).
The modern quantum theory of electromagnetic interaction perfectly describes all known electromagnetic phenomena.
In the 60s and 70s of the century, a unified theory of weak and electromagnetic interactions (the so-called electroweak interaction) of leptons and quarks was basically constructed.
Modern theory strong interaction is quantum chromodynamics.
Attempts are being made to combine the electroweak and strong interactions into the so-called “Grand Unification”, as well as to include them in a single scheme of gravitational interaction.
