For which state does electrodynamics play an important role? Electrodynamics, formulas

DEFINITION

Electromagnetic fields and electromagnetic interactions are studied by a branch of physics called electrodynamics.

Classical electrodynamics studies and describes the properties of electromagnetic fields. Examines the laws by which electromagnetic fields interact with bodies with an electric charge.

Basic concepts of electrodynamics

The basis of the electrodynamics of a stationary medium is Maxwell's equations. Electrodynamics operates with such basic concepts as electromagnetic field, electric charge, electromagnetic potential, Poynting vector.

An electromagnetic field is a special type of matter that manifests itself when one charged body interacts with another. Often, when considering an electromagnetic field, its components are distinguished: electric field and magnetic field. An electric field creates an electric charge or an alternating magnetic field. A magnetic field arises when a charge (charged body) moves and in the presence of a time-varying electric field.

Electromagnetic potential is a physical quantity that determines the distribution of the electromagnetic field in space.

Electrodynamics is divided into: electrostatics; magnetostatics; electrodynamics of continuum; relativistic electrodynamics.

The Poynting vector (Umov-Poynting vector) is a physical quantity that is the vector of the energy flux density of the electromagnetic field. The magnitude of this vector is equal to the energy that is transferred per unit time through a unit surface area that is perpendicular to the direction of propagation of electromagnetic energy.

Electrodynamics forms the basis for the study and development of optics (as a branch of science) and the physics of radio waves. This branch of science is the foundation for radio engineering and electrical engineering.

Classical electrodynamics, when describing the properties of electromagnetic fields and the principles of their interaction, uses Maxwell’s system of equations (in integral or differential forms), supplementing it with a system of material equations, boundary and initial conditions.

Maxwell's structural equations

Maxwell's system of equations has the same meaning in electrodynamics as Newton's laws in classical mechanics. Maxwell's equations were obtained as a result of generalization of numerous experimental data. Maxwell's structural equations are distinguished, writing them in integral or differential form, and material equations that connect vectors with parameters characterizing the electrical and magnetic properties of matter.

Maxwell's structural equations in integral form (in the SI system):

where is the magnetic field strength vector; is the electric current density vector; - electric displacement vector. Equation (1) reflects the law of creation of magnetic fields. A magnetic field occurs when a charge moves (electric current) or when an electric field changes. This equation is a generalization of the Biot-Savart-Laplace law. Equation (1) is called the magnetic field circulation theorem.

where is the magnetic field induction vector; - electric field strength vector; L is a closed loop through which the electric field strength vector circulates. Another name for equation (2) is the law of electromagnetic induction. Expression (2) means that the vortex electric field is generated due to an alternating magnetic field.

where is the electric charge; - charge density. Equation (3) is called the Ostrogradsky-Gauss theorem. Electric charges are sources of electric field; there are free electric charges.

Equation (4) indicates that the magnetic field is vortex. Magnetic charges do not exist in nature.

Maxwell's structural equations in differential form (SI system):

where is the electric field strength vector; - vector of magnetic induction.

where is the magnetic field strength vector; - dielectric displacement vector; - current density vector.

where is the electric charge distribution density.

Maxwell's structural equations in differential form determine the electromagnetic field at any point in space. If charges and currents are distributed continuously in space, then the integral and differential forms of Maxwell's equations are equivalent. However, if there are discontinuity surfaces, then the integral form of writing Maxwell's equations is more general.

To achieve mathematical equivalence of the integral and differential forms of Maxwell's equations, the differential notation is supplemented with boundary conditions.

From Maxwell's equations it follows that an alternating magnetic field generates an alternating electric field and vice versa, that is, these fields are inseparable and form a single electromagnetic field. The sources of the electric field can be either electric charges or a time-varying magnetic field. Magnetic fields are excited by moving electric charges (currents) or alternating electric fields. Maxwell's equations are not symmetric with respect to electric and magnetic fields. This happens because electric charges exist, but magnetic charges do not.

Material equations

Maxwell's system of structural equations is supplemented with material equations that reflect the relationship of vectors with parameters characterizing the electrical and magnetic properties of matter.

where is the relative dielectric constant, is the relative magnetic permeability, is the specific electrical conductivity, is the electrical constant, is the magnetic constant. The medium in this case is considered isotropic, non-ferromagnetic, non-ferroelectric.

Examples of problem solving

EXAMPLE 1

Exercise Derive the differential form of the continuity equation from Maxwell's system of equations.
Solution As a basis for solving the problem, we use the equation:

where is the area of ​​an arbitrary surface on which the closed contour L rests. From (1.1) we have:

Consider an infinitesimal contour, then

Since the surface is closed, expression (1.2) can be rewritten as:

Let's write another Maxwell equation:

Let us differentiate equation (1.5) with respect to time, we have:

Taking into account expression (1.4), equation (1.5) can be presented as:

We have obtained continuity equation (1.5) in integral form. In order to move to the differential form of the continuity equation, let's go to the limit:

We have obtained the continuity equation in differential form:

FUNDAMENTALS OF ELECTRODYNAMICS. ELECTROSTATICS


FUNDAMENTALS OF ELECTRODYNAMICS

Electrodynamics- the science of the properties of the electromagnetic field.

Electromagnetic field- determined by the movement and interaction of charged particles.

Manifestation of electric/magnetic field- this is the action of electric/magnetic forces:
1) frictional forces and elastic forces in the macrocosm;
2) the action of electric/magnetic forces in the microcosm (atomic structure, coupling of atoms into molecules,
transformation of elementary particles)

Discovery of the electric/magnetic field- J. Maxwell.


ELECTROSTATICS

The branch of electrodynamics studies electrically charged bodies at rest.

Elementary particles may have email charge, then they are called charged;
- interact with each other with forces that depend on the distance between particles,
but exceed many times the forces of mutual gravity (this interaction is called
electromagnetic).

Email charge- physical value determines the intensity of electric/magnetic interactions.
There are 2 signs of electric charges: positive and negative.
Particles with like charges repel, and particles with unlike charges attract.
A proton has a positive charge, an electron has a negative charge, and a neutron is electrically neutral.

Elementary charge- a minimum charge that cannot be divided.
How can we explain the presence of electromagnetic forces in nature?
- All bodies contain charged particles.
In the normal state of the body, el. neutral (since the atom is neutral), and electric/magnetic. powers are not manifested.

Body is charged, if it has an excess of charges of any sign:
negatively charged - if there is an excess of electrons;
positively charged - if there is a lack of electrons.

Electrification of bodies- this is one of the ways to obtain charged bodies, for example, by contact).
In this case, both bodies are charged, and the charges are opposite in sign, but equal in magnitude.


Law of conservation of electric charge.

In a closed system, the algebraic sum of the charges of all particles remains unchanged.
(... but not the number of charged particles, since there are transformations of elementary particles).

Closed system

A system of particles into which charged particles do not enter from the outside and do not exit.

Coulomb's law

Basic law of electrostatics.

The force of interaction between two point stationary charged bodies in a vacuum is directly proportional
the product of the charge modules and is inversely proportional to the square of the distance between them.

When bodies are considered point bodies? - if the distance between them is many times greater than the size of the bodies.
If two bodies have electric charges, then they interact according to Coulomb's law.



Unit of electric charge
1 C is a charge passing through the cross-section of a conductor in 1 second at a current of 1 A.
1 C is a very large charge.
Elemental charge:

ELECTRIC FIELD

There is an electrical charge around, materially.
The main property of the electric field: the action with force on the electric charge introduced into it.

Electrostatic field- the field of a stationary electric charge does not change with time.

Electric field strength.- quantitative characteristics of el. fields.
is the ratio of the force with which the field acts on the introduced point charge to the magnitude of this charge.
- does not depend on the magnitude of the introduced charge, but characterizes the electric field!

Tension vector direction
coincides with the direction of the force vector acting on a positive charge, and opposite to the direction of the force acting on a negative charge.

Point charge field strength:


where q0 is the charge creating the electric field.
At any point in the field, the intensity is always directed along the straight line connecting this point and q0.

ELECTRIC CAPACITY

Characterizes the ability of two conductors to accumulate electrical charge.
- does not depend on q and U.
- depends on the geometric dimensions of the conductors, their shape, relative position, electrical properties of the medium between the conductors.

SI units: (F - farad)

CAPACITORS

Electrical device that stores charge
(two conductors separated by a dielectric layer).

Where d is much smaller than the dimensions of the conductor.

Designation on electrical diagrams:


The entire electric field is concentrated inside the capacitor.
The charge of a capacitor is the absolute value of the charge on one of the capacitor plates.

Types of capacitors:
1. by type of dielectric: air, mica, ceramic, electrolytic
2. according to the shape of the plates: flat, spherical.
3. by capacity: constant, variable (adjustable).



Electrical capacitance of a flat capacitor

where S is the area of ​​the plate (plating) of the capacitor
d - distance between plates
eo - electrical constant
e - dielectric constant of the dielectric

Including capacitors in an electrical circuit

parallel

sequential

Then the total electrical capacity (C):

when connected in parallel

.

when connected in series

DC AC CONNECTIONS

Electricity- ordered movement of charged particles (free electrons or ions).
In this case, electricity is transferred through the cross section of the conductor. charge (during the thermal movement of charged particles, the total transferred electrical charge = 0, since positive and negative charges are compensated).

Email direction current- it is conventionally accepted to consider the direction of movement of positively charged particles (from + to -).

Email actions current (in conductor):

thermal effect of current- heating of the conductor (except for superconductors);

chemical effect of current - appears only in electrolytes. Substances that make up the electrolyte are released on the electrodes;

magnetic effect of current(main) - observed in all conductors (deflection of the magnetic needle near a conductor with current and the force effect of the current on adjacent conductors through a magnetic field).

OHM'S LAW FOR A CIRCUIT SECTION

where , R is the resistance of the circuit section. (the conductor itself can also be considered a section of the circuit).

Each conductor has its own specific current-voltage characteristic.

RESISTANCE

Basic electrical characteristics of a conductor.
- according to Ohm's law, this value is constant for a given conductor.

1 Ohm is the resistance of a conductor with a potential difference at its ends
at 1 V and the current strength in it is 1 A.

Resistance depends only on the properties of the conductor:

where S is the cross-sectional area of ​​the conductor, l is the length of the conductor,
ro - resistivity characterizing the properties of the conductor substance.


ELECTRICAL CIRCUITS

They consist of a source, a consumer of electric current, wires, and a switch.

SERIES CONNECTION OF CONDUCTORS

I - current strength in the circuit
U - voltage at the ends of the circuit section

PARALLEL CONNECTION OF CONDUCTORS

I - current strength in an unbranched section of the circuit
U - voltage at the ends of the circuit section
R - total resistance of the circuit section

Remember how measuring instruments are connected:

Ammeter - connected in series with the conductor in which the current is measured.

Voltmeter - connected in parallel to the conductor on which the voltage is measured.

DC OPERATION

Current work- this is the work of the electric field to transfer electric charges along the conductor;

The work done by the current on a section of the circuit is equal to the product of the current, voltage and time during which the work was performed.

Using the formula of Ohm's law for a section of a circuit, you can write several versions of the formula for calculating the work of the current:

According to the law of conservation of energy:

The work is equal to the change in the energy of a section of the circuit, so the energy released by the conductor is equal to the work of the current.

In the SI system:

JOULE-LENZ LAW

When current passes through a conductor, the conductor heats up and heat exchange occurs with the environment, i.e. the conductor gives off heat to the bodies surrounding it.

The amount of heat released by a conductor carrying current into the environment is equal to the product of the square of the current strength, the resistance of the conductor and the time the current passes through the conductor.

According to the law of conservation of energy, the amount of heat released by a conductor is numerically equal to the work done by the current flowing through the conductor during the same time.

In the SI system:

[Q] = 1 J

DC POWER

The ratio of the work done by the current during time t to this time interval.

In the SI system:

The phenomenon of superconductivity

Discovery of low temperature superconductivity:
1911 - Dutch scientist Kamerling - Onnes
observed at ultra-low temperatures (below 25 K) in many metals and alloys;
At such temperatures, the resistivity of these substances becomes vanishingly small.

In 1957, a theoretical explanation of the phenomenon of superconductivity was given:
Cooper (USA), Bogolyubov (USSR)

1957 Collins's experiment: the current in a closed circuit without a current source did not stop for 2.5 years.

In 1986, high-temperature superconductivity (at 100 K) was discovered (for metal-ceramics).


Difficulty of achieving superconductivity:
- the need for strong cooling of the substance


Application area:
- obtaining strong magnetic fields;
- powerful electromagnets with superconducting winding in accelerators and generators.

Currently in the energy sector there is a big problem
- large losses of electricity during transmission her by wire.


Possible Solution Problems:
with superconductivity, the resistance of the conductors is approximately 0
and energy losses are sharply reduced.

Substance with the highest superconducting temperature
In 1988 in the USA, at a temperature of –148°C, the phenomenon of superconductivity was obtained. The conductor was a mixture of thallium, calcium, barium and copper oxides - Tl2Ca2Ba2Cu3Ox.

Semiconductor -

A substance whose resistivity can vary over a wide range and decreases very quickly with increasing temperature, which means that the electrical conductivity (1/R) increases.
- observed in silicon, germanium, selenium and some compounds.

Conduction mechanism in semiconductors

Semiconductor crystals have an atomic crystal lattice where outer electrons are bonded to neighboring atoms by covalent bonds.
At low temperatures, pure semiconductors have no free electrons and behave like an insulator.

ELECTRIC CURRENT IN VACUUM

What is a vacuum?
- this is the degree of rarefaction of a gas at which there are practically no collisions of molecules;

Electric current is not possible because the possible number of ionized molecules cannot provide electrical conductivity;
- it is possible to create electric current in a vacuum if you use a source of charged particles;
- the action of a source of charged particles can be based on the phenomenon of thermionic emission.

Thermionic emission

- this is the emission of electrons by solid or liquid bodies when they are heated to temperatures corresponding to the visible glow of hot metal.
The heated metal electrode continuously emits electrons, forming an electron cloud around itself.
In an equilibrium state, the number of electrons that left the electrode is equal to the number of electrons that returned to it (since the electrode becomes positively charged when electrons are lost).
The higher the temperature of the metal, the higher the density of the electron cloud.

Vacuum diode

Electric current in a vacuum is possible in vacuum tubes.
A vacuum tube is a device that uses the phenomenon of thermionic emission.

A vacuum diode is a two-electrode (A - anode and K - cathode) electron tube.
Very low pressure is created inside the glass container

H - filament placed inside the cathode to heat it. The surface of the heated cathode emits electrons. If the anode is connected to + of the current source, and the cathode is connected to -, then the circuit flows
constant thermionic current. The vacuum diode has one-way conductivity.
Those. current in the anode is possible if the anode potential is higher than the cathode potential. In this case, electrons from the electron cloud are attracted to the anode, creating an electric current in a vacuum.

Current-voltage characteristic of a vacuum diode.

At low anode voltages, not all the electrons emitted by the cathode reach the anode, and the electric current is small. At high voltages, the current reaches saturation, i.e. maximum value.
A vacuum diode is used to rectify alternating current.

Current at the input of the diode rectifier:


Rectifier output current:

Electron beams

This is a stream of rapidly flying electrons in vacuum tubes and gas-discharge devices.

Properties of electron beams:

Deflects in electric fields;
- deflect in magnetic fields under the influence of the Lorentz force;
- when a beam hitting a substance is decelerated, X-ray radiation appears;
- causes glow (luminescence) of some solids and liquids (luminophores);
- heat the substance by contacting it.

Cathode ray tube (CRT)

Thermionic emission phenomena and properties of electron beams are used.

A CRT consists of an electron gun, horizontal and vertical deflectors
electrode plates and screen.
In an electron gun, electrons emitted by a heated cathode pass through the control grid electrode and are accelerated by the anodes. An electron gun focuses an electron beam into a point and changes the brightness of the light on the screen. Deflecting horizontal and vertical plates allow you to move the electron beam on the screen to any point on the screen. The tube screen is coated with a phosphor that begins to glow when bombarded with electrons.

There are two types of tubes:

1) with electrostatic control of the electron beam (deflection of the electric beam only by the electric field);
2) with electromagnetic control (magnetic deflection coils are added).

Main applications of CRT:

picture tubes in television equipment;
computer displays;
electronic oscilloscopes in measuring technology.

ELECTRIC CURRENT IN GASES

Under normal conditions, gas is a dielectric, i.e. it consists of neutral atoms and molecules and does not contain free carriers of electric current.
The conductor gas is an ionized gas. Ionized gas has electron-ion conductivity.

Air is a dielectric in power lines, air capacitors, and contact switches.

Air is a conductor when lightning, an electric spark occurs, or when a welding arc occurs.


Gas ionization

It is the breakdown of neutral atoms or molecules into positive ions and electrons by removing electrons from the atoms. Ionization occurs when a gas is heated or exposed to radiation (UV, X-rays, radioactive) and is explained by the disintegration of atoms and molecules during collisions at high speeds.

Gas discharge

This is electric current in ionized gases.
The charge carriers are positive ions and electrons. Gas discharge is observed in gas-discharge tubes (lamps) when exposed to an electric or magnetic field.

Recombination of charged particles


- the gas ceases to be a conductor if ionization stops, this occurs as a result of recombination (reunion of oppositely charged particles).

There is a self-sustaining and non-self-sustaining gas discharge.

Non-self-sustaining gas discharge

If the action of the ionizer is stopped, the discharge will also stop.

When the discharge reaches saturation, the graph becomes horizontal. Here, the electrical conductivity of the gas is caused only by the action of the ionizer.

Self-sustaining gas discharge

In this case, the gas discharge continues even after the termination of the external ionizer due to ions and electrons resulting from impact ionization (= ionization of electric shock); occurs when the potential difference between the electrodes increases (an electron avalanche occurs).
A non-self-sustained gas discharge can transform into a self-sustained gas discharge when Ua = Uignition.

Electrical breakdown of gas

The process of transition of a non-self-sustaining gas discharge into a self-sustaining one.

Self-sustained gas discharge occurs 4 types:

1. smoldering - at low pressures (up to several mm Hg) - observed in gas-light tubes and gas lasers.
2. spark - at normal pressure and high electric field strength (lightning - current strength up to hundreds of thousands of amperes).
3. corona - at normal pressure in a non-uniform electric field (at the tip).
4. arc - high current density, low voltage between the electrodes (gas temperature in the arc channel -5000-6000 degrees Celsius); observed in spotlights and projection film equipment.

These discharges are observed:

smoldering - in fluorescent lamps;
spark - in lightning;
corona - in electric precipitators, during energy leakage;
arc - during welding, in mercury lamps.


Plasma

This is the fourth state of aggregation of a substance with a high degree of ionization due to the collision of molecules at high speed at high temperature; found in nature: ionosphere - weakly ionized plasma, Sun - fully ionized plasma; artificial plasma - in gas-discharge lamps.

Plasma can be:

Low temperature - at temperatures less than 100,000K;
high temperature - at temperatures above 100,000K.

Basic properties of plasma:

High electrical conductivity
- strong interaction with external electric and magnetic fields.

At a temperature

Any substance is in a plasma state.

Interestingly, 99% of the matter in the Universe is plasma

TEST QUESTIONS FOR TESTING



Plan:

    Introduction
  • 1 Basic Concepts
  • 2 Basic Equations
  • 3 Contents of electrodynamics
  • 4 Sections of electrodynamics
  • 5 Application value
  • 6 History

Introduction

Electrodynamics- a branch of physics that studies the electromagnetic field in the most general case (that is, time-dependent variable fields are considered) and its interaction with bodies that have an electric charge (electromagnetic interaction). The subject of electrodynamics includes the connection between electrical and magnetic phenomena, electromagnetic radiation (in different conditions, both free and in various cases of interaction with matter), electric current (generally speaking, variable) and its interaction with the electromagnetic field (electric current can be considered when this is like a collection of moving charged particles). Any electrical and magnetic interaction between charged bodies is considered in modern physics as occurring through an electromagnetic field, and, therefore, is also the subject of electrodynamics.

Most often under the term electrodynamics by default, classical (not affecting quantum effects) electrodynamics is understood; To denote the modern quantum theory of the electromagnetic field and its interaction with charged particles, the stable term quantum electrodynamics is usually used.


1. Basic concepts

The basic concepts used in electrodynamics include:

  • The electromagnetic field is the main subject of study of electrodynamics, a type of matter that manifests itself when interacting with charged bodies. Historically divided into two fields:
    • Electric field - created by any charged body or alternating magnetic field, has an effect on any charged body.
    • Magnetic field - created by moving charged bodies, charged bodies with spin, and alternating electric fields, affects moving charges and charged bodies with spin.
  • Electric charge is a property of bodies that allows them to create electromagnetic fields, as well as interact with these fields.
  • Electromagnetic potential is a 4-vector physical quantity that completely determines the distribution of the electromagnetic field in space. Highlight:
    • Electrostatic potential - time component of a 4-vector
    • Vector potential is a three-dimensional vector formed by the remaining components of a 4-vector.
  • The Poynting vector is a vector physical quantity that has the meaning of the energy flux density of an electromagnetic field.

2. Basic equations

The basic equations describing the behavior of the electromagnetic field and its interaction with charged bodies are:

  • Maxwell's equations, which determine the behavior of a free electromagnetic field in a vacuum and a medium, as well as the generation of the field by sources. Among these equations are:
    • Faraday's law of induction, which determines the generation of an electric field by an alternating magnetic field.
    • The magnetic field circulation theorem with the addition of displacement currents introduced by Maxwell determines the generation of a magnetic field by moving charges and an alternating electric field
    • Gauss's theorem for the electric field, which determines the generation of an electrostatic field by charges.
    • The law of closure of magnetic field lines.
  • An expression for the Lorentz force that determines the force acting on a charge located in an electromagnetic field.
  • The Joule-Lenz law, which determines the amount of heat loss in a conducting medium with finite conductivity, in the presence of an electric field in it.

Particular equations of particular importance are:

  • Coulomb's law, which combines Gauss' theorem for the electric field and the Lorentz force, and determines the electrostatic interaction of two point charges.
  • Ampere's law, which determines the force acting on an elementary current placed in a magnetic field.
  • Poynting's theorem, which expresses the law of conservation of energy in electrodynamics.

3. Contents of electrodynamics

The main content of classical electrodynamics is the description of the properties of the electromagnetic field and its interaction with charged bodies (charged bodies “generate” the electromagnetic field, are its “sources,” and the electromagnetic field in turn acts on charged bodies, creating electromagnetic forces). This description, in addition to defining basic objects and quantities, such as electric charge, electric field, magnetic field, electromagnetic potential, is reduced to Maxwell’s equations in one form or another and the Lorentz force formula, and also touches on some related issues (related to mathematical physics, applications, auxiliary quantities and auxiliary formulas important for applications, such as the current density vector or empirical Ohm's law). This description also includes issues of conservation and transfer of energy, momentum, angular momentum by an electromagnetic field, including formulas for energy density, Poynting vector, etc.

Sometimes, electrodynamic effects (as opposed to electrostatics) are understood as those significant differences between the general case of the behavior of the electromagnetic field (for example, the dynamic relationship between changing electric and magnetic fields) from the static case, which make the particular static case much simpler to describe, understand and calculate.


4. Sections of electrodynamics

  • Electrostatics describes the properties of a static (not changing with time or changing slowly enough that “electrodynamic effects” in the sense described above can be neglected) electric field and its interaction with electrically charged bodies (electric charges).
  • Magnetostatics studies direct currents and constant magnetic fields (the fields do not change over time or change so slowly that the speed of these changes can be neglected in the calculation), as well as their interaction.
  • Continuum electrodynamics examines the behavior of electromagnetic fields in continuous media.
  • Relativistic electrodynamics considers electromagnetic fields in moving media.

5. Application value

Electrodynamics underlies physical optics, the physics of radio wave propagation, and also permeates almost all physics, since almost all branches of physics have to deal with electric fields and charges, and often with their non-trivial rapid changes and movements. In addition, electrodynamics is an exemplary physical theory (both in its classical and quantum versions), combining very high accuracy of calculations and predictions with the influence of theoretical ideas born in its field on other areas of theoretical physics.

Electrodynamics is of great importance in technology and forms the basis of: radio engineering, electrical engineering, various branches of communications and radio.


6. History

The first proof of the connection between electrical and magnetic phenomena was Oersted's experimental discovery in 1819-1820 of the generation of a magnetic field by electric current. He also expressed the idea of ​​some interaction of electrical and magnetic processes in the space surrounding the conductor, but in a rather unclear form.

In 1831, Michael Faraday experimentally discovered the phenomenon and law of electromagnetic induction, which became the first clear evidence of the direct dynamic relationship of electric and magnetic fields. He also developed (in relation to electric and magnetic fields) the fundamentals of the concept of a physical field and some basic theoretical concepts that make it possible to describe physical fields, and also predicted the existence of electromagnetic waves in 1832.

In 1864, J. C. Maxwell first published the complete system of equations of "classical electrodynamics" describing the evolution of the electromagnetic field and its interaction with charges and currents. He made a theoretically based assumption that light is an electromagnetic wave, i.e. object of electrodynamics.

Electrodynamics… Spelling dictionary-reference book

Classical theory (non-quantum) of the behavior of the electromagnetic field, which carries out the interaction between electrical. charges (electromagnetic interaction). Classical laws macroscopic E. are formulated in Maxwell’s equations, which allow ... Physical encyclopedia

- (from the word electricity, and Greek dinamis power). Part of physics that deals with the action of electric currents. Dictionary of foreign words included in the Russian language. Chudinov A.N., 1910. ELECTRODYNAMICS from the word electricity, and Greek. dynamis, strength... Dictionary of foreign words of the Russian language

Modern encyclopedia

Electrodynamics- classical, theory of non-quantum electromagnetic processes in which the main role is played by interactions between charged particles in various media and in vacuum. The formation of electrodynamics was preceded by the works of C. Coulomb, J. Biot, F. Savart, ... ... Illustrated Encyclopedic Dictionary

Classical theory of electromagnetic processes in various media and in vacuum. Covers a huge set of phenomena in which the main role is played by interactions between charged particles carried out through an electromagnetic field... Big Encyclopedic Dictionary

ELECTRODYNAMICS, in physics, the field that studies the interaction between electric and magnetic fields and charged bodies. This discipline began in the 19th century. with her theoretical works James MAXWELL, she later became part of... ... Scientific and technical encyclopedic dictionary

ELECTRODYNAMICS, electrodynamics, many others. no, female (see electricity and dynamics) (physical). Department of physics, studying the properties of electric current, electricity in motion; ant. electrostatics. Ushakov's explanatory dictionary. D.N. Ushakov. 1935 1940 … Ushakov's Explanatory Dictionary

ELECTRODYNAMICS, and, g. (specialist.). Theory of electromagnetic processes in various media and in vacuum. Ozhegov's explanatory dictionary. S.I. Ozhegov, N.Yu. Shvedova. 1949 1992 … Ozhegov's Explanatory Dictionary

Noun, number of synonyms: 2 dynamics (18) physics (55) ASIS dictionary of synonyms. V.N. Trishin. 2013… Synonym dictionary

electrodynamics- - [A.S. Goldberg. English-Russian energy dictionary. 2006] Topics of power engineering in general EN electrodynamics ... Technical Translator's Guide

Books

  • Electrodynamics, A. E. Ivanov. This textbook is self-sufficient: it presents lectures that were given for a number of years by an associate professor at the specialized educational and scientific center of MSTU. N. E. Bauman...
  • Electrodynamics, Sergei Anatolyevich Ivanov. ...

Definition 1

Electrodynamics is a huge and important field of physics that studies the classical, non-quantum properties of the electromagnetic field and the motion of positively charged magnetic charges interacting with each other using this field.

Figure 1. Briefly about electrodynamics. Author24 - online exchange of student works

Electrodynamics seems to be a wide range of different formulations of problems and their intelligent solutions, approximate methods and special cases, which are combined into one whole by general initial laws and equations. The latter, making up the main part of classical electrodynamics, are presented in detail in Maxwell's formulas. Currently, scientists continue to study the principles of this area in physics, the skeleton of its construction, relationships with other scientific areas.

Coulomb's law in electrodynamics is denoted as follows: $F= \frac (kq1q2) (r2)$, where $k= \frac (9 \cdot 10 (H \cdot m)) (Kl)$. The electric field strength equation is written as follows: $E= \frac (F)(q)$, and the flux of the magnetic field induction vector $∆Ф=В∆S \cos (a)$.

In electrodynamics, free charges and systems of charges, which contribute to the activation of a continuous energy spectrum, are primarily studied. The classical description of electromagnetic interaction is favored by the fact that it is effective already in the low-energy limit, when the energy potential of particles and photons is small compared to the rest energy of the electron.

In such situations, there is often no annihilation of charged particles, since there is only a gradual change in the state of their unstable motion as a result of the exchange of a large number of low-energy photons.

Note 1

However, even at high energies of particles in the medium, despite the significant role of fluctuations, electrodynamics can be successfully used for a comprehensive description of statistically average, macroscopic characteristics and processes.

Basic equations of electrodynamics

The main formulas that describe the behavior of the electromagnetic field and its direct interaction with charged bodies are Maxwell’s equations, which determine the probable actions of a free electromagnetic field in a medium and vacuum, as well as the general generation of the field by sources.

Among these provisions in physics it is possible to highlight:

  • Gauss's theorem for the electric field - intended to determine the generation of an electrostatic field by positive charges;
  • hypothesis of closed field lines - promotes the interaction of processes within the magnetic field itself;
  • Faraday's law of induction - establishes the generation of electric and magnetic fields by the variable properties of the environment.

In general, the Ampere-Maxwell theorem is a unique idea about the circulation of lines in a magnetic field with the gradual addition of displacement currents introduced by Maxwell himself, which precisely determines the transformation of the magnetic field by moving charges and the alternating action of the electric field.

Charge and force in electrodynamics

In electrodynamics, the interaction of force and charge of the electromagnetic field comes from the following joint definition of the electric charge $q$, energy $E$ and magnetic $B$ fields, which are established as a fundamental physical law based on the entire set of experimental data. The formula for the Lorentz force (within the idealization of a point charge moving at a certain speed) is written with the replacement of the speed $v$.

Conductors often contain a huge amount of charges, therefore, these charges are fairly well compensated: the number of positive and negative charges is always equal to each other. Consequently, the total electric force that constantly acts on the conductor is also zero. The magnetic forces operating on individual charges in a conductor are ultimately not compensated, because in the presence of current, the speeds of movement of the charges are always different. The equation for the action of a conductor with current in a magnetic field can be written as follows: $G = |v ⃗ |s \cos(a) $

If we study not a liquid, but a full and stable flow of charged particles as a current, then the entire energy potential passing linearly through the area for $1s$ will be the current strength equal to: $I = ρ| \vec (v) |s \cos(a) $, where $ρ$ is the charge density (per unit volume in the total flow).

Note 2

If the magnetic and electric field systematically changes from point to point on a specific site, then in the expressions and formulas for partial flows, as in the case of a liquid, the average values ​​$E ⃗ $ and $B ⃗$ on the site must be entered.

The special position of electrodynamics in physics

The significant position of electrodynamics in modern science can be confirmed through the famous work of A. Einstein, in which the principles and foundations of the special theory of relativity were outlined in detail. The scientific work of the outstanding scientist is called “On the electrodynamics of moving bodies,” and includes a huge number of important equations and definitions.

As a separate field of physics, electrodynamics consists of the following sections:

  • the doctrine of the field of stationary but electrically charged physical bodies and particles;
  • the doctrine of the properties of electric current;
  • the doctrine of the interaction of magnetic field and electromagnetic induction;
  • the study of electromagnetic waves and oscillations.

All of the above sections are united into one by the theorem of D. Maxwell, who not only created and presented a coherent theory of the electromagnetic field, but also described all its properties, proving its real existence. The work of this particular scientist showed the scientific world that the electric and magnetic fields known at that time are just a manifestation of a single electromagnetic field operating in different reference systems.

A significant part of physics is devoted to the study of electrodynamics and electromagnetic phenomena. This area largely lays claim to the status of a separate science, since it not only explores all the patterns of electromagnetic interactions, but also describes them in detail through mathematical formulas. Deep and long-term research in electrodynamics has opened new ways for the use of electromagnetic phenomena in practice, for the benefit of all mankind.