Ministry of Education of the Russian Federation
St. Petersburg Institute of Mechanical Engineering
Rabstractin Physics
on the topic of:
"The Essence of Maxwell's Electromagnetic Theory"
Performed:
student gr. 2801
Shkeneva Yu.A.
Saint Petersburg
Introduction 3
Vortex electric field 6
Bias current 7
Maxwell's equation for the electromagnetic field 9
List of references 13
Introduction
James Clerk Maxwell was born on June 13, 1831. in Edinburgh, in the family of a lawyer who owned an estate in Scotland. The boy showed an early love for technology and a desire to understand the world around him. His father, a highly educated man who was deeply interested in the problems of natural science and technology, had a great influence on him. At school, Maxwell was fascinated by geometry, and his first scientific work, completed at the age of fifteen, was the discovery of a simple but unknown method of drawing oval figures. Maxwell received a good education, first at Edinburgh and then at Cambridge universities.
In 1856, a young, promising scientist was invited to teach as a professor at a college in the Scottish city of Aberdeen. Here Maxwell enthusiastically works on problems of theoretical and applied mechanics, optics, and the physiology of color vision. He brilliantly solves the mystery of Saturn's rings, mathematically proving that they are formed from individual particles. The scientist's name becomes known, and he is invited to take a chair at King's College in London. The London period (1860-1865) was the most fruitful in the scientist's life. He resumes and brings to completion theoretical research in electrodynamics, publishes fundamental works on the kinetic theory of gases.
After moving from Aberdeen, Maxwell continued his research with unremitting effort, paying especially much attention to the kinetic theory of gases. It is said that his wife (the former Catherine Mary Dewar, daughter of the head of Marischal College) lit a fire in the basement of their London house to enable Maxwell to conduct experiments in the attic on the thermal properties of gases. But Maxwell's decisive and certainly greatest achievement was his creation of electromagnetic theory.
The early nineteenth century was full of exciting discoveries. Soon after obtaining the first stationary currents, Oersted showed that current flowing through a conductor generates magnetic effects similar to those caused by an ordinary permanent magnet. Therefore, it was assumed that two current-carrying conductors should behave like two magnets, which, as is known, can either attract or repel. Indeed, experiments by Ampere and other researchers confirmed the presence of attractive or repulsive forces between two current-carrying conductors. Soon it was possible to formulate the law of attraction and repulsion with the same precision with which Newton formulated the law of gravitational attraction between any two material bodies.
Faraday and Henry then discovered the remarkable phenomenon of electromagnetic induction and thereby demonstrated the close connection between magnetism and electricity.
However, there was an urgent need to create a unified theory that met the necessary requirements, which would make it possible to predict the development of electromagnetic phenomena in time and space in the most general case, under any conceivable specific experimental conditions.
This is exactly what Maxwell’s electromagnetic theory turned out to be, formulated by him in the form of a system of several equations that describe the entire variety of properties of electromagnetic fields using two physical quantities - the electric field strength E and the magnetic field strength H. It is remarkable that these Maxwell equations in their final form and to this day remain the cornerstone of physics, providing a true-to-life description of observed electromagnetic phenomena.
When designing a high-voltage line to transmit electricity over long distances, Maxwell's equations help create a system that ensures a minimum of losses; when conducting fundamental experiments in the laboratory to study the properties of metals in a high-frequency electric field at very low temperatures, we use Maxwell’s equations to determine the nature of the propagation of the electromagnetic field inside the metal; If we are building a new radio telescope capable of capturing the electromagnetic noise of space, then when designing antennas and waveguides that transfer energy from the antenna to the radio receiver, we invariably use Maxwell's equations.
There is a law according to which the force acting on a charge moving in a magnetic field is directly proportional to the product of the magnitude of the charge and the velocity component perpendicular to the direction of the magnetic field; this force is known to us as the “Lorentz force”. However, someone calls it "Laplace's force."
There is no such uncertainty regarding Maxwell's equations; the credit for this discovery belongs to him alone.
It should be noted that in the last century he was by no means the only physicist who tried to create a comprehensive theory of electromagnetism; others also, not without reason, suspected the existence of a deep connection between light and electrical phenomena.
Maxwell's main merit is that he, in his own way, came to an elegant and simple system of equations that describes all electromagnetic phenomena.
Maxwell's equations not only cover and describe all electromagnetic phenomena known to us; the scope of their application is not limited even to any conceivable electromagnetic phenomena occurring in specific local conditions. Maxwell's theory predicted a completely new effect, observed in space free from material bodies - electromagnetic radiation. This is certainly a unique achievement, crowning the triumph of Maxwell's theory.
Vortex electric field
From Faraday's law e i = - d Ф/dt it follows that any change in the magnetic induction flux associated with the circuit leads to the appearance of an electromotive force of induction and as a result of this an induced current appears. Consequently, the occurrence of emf. electromagnetic induction is also possible in a stationary circuit located in an alternating magnetic field. However, the e.m.f. in any circuit occurs only when external forces act on current carriers in it - forces of non-electrostatic origin.
Experience shows that these extraneous forces are not associated with either thermal or chemical processes in the circuit; their occurrence also cannot be explained by Lorentz forces, since they do not act on stationary charges. Maxwell hypothesized that any alternating magnetic field excites an electric field in the surrounding space, which is the cause of the appearance of induced current in the circuit. According to Maxwell's ideas, the circuit in which the emf appears plays a secondary role, being a kind of only a “device” that detects this field.
So, according to Maxwell, a time-varying magnetic field generates an electric field E B, the circulation of which, according to the formula,
E B dl = E Bl dl = - d Ф/dt (1)
where, the projection of the vector E Bl is the projection of the vector E to the direction dl; the partial derivative ¶Ф/¶t takes into account the dependence of the magnetic induction flux only on time.
Substituting the expression Ф = B dS into this formula (1), we obtain
E B dl = - ¶ / ¶ t B dS
Since the contour and surface are motionless, the operations of differentiation and integration can be swapped. Hence,
E B dl = - ¶ B/ ¶ t dS (2)
According to E dl = El dl = 0, the circulation of the electrostatic field strength vector (let’s denote it E Q) along a closed loop is zero:
E Q dl = E Ql dl = 0 (3)
Comparing expressions (1) and (3), we see that there is a fundamental difference between the fields under consideration (E B and E Q): the circulation of the vector E B, in contrast to the circulation of the vector E Q, is not zero. Consequently, the electric field E B excited by the magnetic field, like the magnetic field itself, is a vortex.
Bias current
According to Maxwell, if any alternating magnetic field excites a vortex electric field in the surrounding space, then the opposite phenomenon should also exist: any change in the electric field should cause the appearance of a vortex magnetic field in the surrounding space. Since a magnetic field is always associated with an electric current, Maxwell called the alternating electric field that excites the magnetic field a displacement current, in contrast to a conduction current caused by the ordered movement of charges. For the occurrence of a displacement current, according to Maxwell, only the existence of an alternating electric field is necessary.
Consider an alternating current circuit containing a capacitor (Fig. 1). There is an alternating electric field between the plates of a charging and discharging capacitor, therefore, according to Maxwell, displacement currents “flow” through the capacitor, and in those areas where there are no conductors. Consequently, since there is an alternating electric field (displacement current) between the plates of the capacitor, a magnetic field is also excited between them.
Let's find a quantitative relationship between the changing electric and the magnetic fields it causes. According to Maxwell, an alternating electric field in a capacitor at each moment of time creates such a magnetic field as if there were a conduction current between the plates of the capacitor with a force equal to the strength of the currents in the supply wires. Then we can say that the conduction current densities (j) and displacement current (j cm) are equal: j cm = j.
Conduction current density near the capacitor plates j = = = ()= d s /dt , s is the surface charge density, S is the area of the capacitor plates. Therefore, j cm = d s /dt (4). If the electrical displacement in the capacitor is equal to D, then the surface charge density on the plates is s = D. Taking this into account, expression (4) can be written as: j cm = ¶ D /¶ t, where the sign of the partial derivative indicates that the magnetic field is determined only by the rate of change of the electric displacement over time.
Since a displacement current occurs with any change in the electric field, it exists not only in a vacuum or dielectrics, but also inside conductors through which alternating current flows. However, in this case it is negligible compared to the conduction current. The presence of displacement currents was confirmed experimentally by the Soviet physicist A. A. Eikhenvald, who studied the magnetic field of the polarization current, which is part of the displacement current.
In the general case, conduction and displacement currents are not separated in space; they are located in the same volume. Maxwell therefore introduced the concept of total current, equal to the sum of conduction currents (as well as convection currents) and displacement. Total current density:
j full = j + ¶ D /¶ t .
By introducing the concept of displacement current and total current, Maxwell took a new approach to considering the closed circuits of alternating current circuits. The total current in them is always closed, i.e. At the ends of the conductor only the conduction current is interrupted, and in the dielectric (vacuum) between the ends of the conductor there is a displacement current that closes the conduction current.
Maxwell generalized the theorem on the circulation of the vector H by introducing into its right side the total current I total = j total dS, covered by a closed loop L. Then the generalized theorem on the circulation of vector H will be written as:
H dl = (j + ¶ D/ ¶ t) dS (5)
Expression (5) is always true, as evidenced by the complete correspondence between theory and experience.
Maxwell's equation for the electromagnetic field
Maxwell's introduction of the concept of displacement current led him to the completion of his unified macroscopic theory of the electromagnetic field, which made it possible from a unified point of view not only to explain electrical and magnetic phenomena, but also to predict new ones, the existence of which was subsequently confirmed.
Maxwell's theory is based on the four equations discussed above:
The electric field can be either potential (E Q) or vortex (E B), so the total field strength is E = E Q + E B. Since the circulation of the vector E Q is equal to zero, and the circulation of the vector E B is determined by expression (2), then the circulation of the total field strength vector
E dl = - ¶B/¶t dS.
This equation shows that the source of the electric field can be not only electric charges, but also time-varying magnetic fields.
Generalized theorem on the circulation of the vector H:
H dl = (j + ¶D/¶t) dS.
This equation shows that magnetic fields can be excited either by moving charges (electric currents) or by alternating electric fields.
Gauss's theorem for the electrostatic field in a dielectric:
If the charge is distributed continuously inside a closed surface with volume density ρ, then formula (6) will be written as:
D dS = ρ dV.
Gauss's theorem for field B:
B dS = 0.
So, the complete system of Maxwell’s equations in integral form:
E dl = - ¶ B/ ¶ t dS; D dS = ρ dV;
H dl = (j + ¶D/¶t) dS; B dS = 0.
The quantities included in Maxwell’s equations are not independent and the following relationship exists between them:
B = m 0 m H;
J = g E ;
where e 0 and m 0 are the electric and magnetic constants, respectively, e and m are the dielectric and magnetic permeabilities, respectively, g is the specific conductivity of the substance.
From Maxwell's equation it follows that the sources of the electric field can be either electric charges or time-varying magnetic fields, and magnetic fields can be excited either by moving electric charges (electric currents) or by alternating electric fields. Maxwell's equations are not symmetrical with respect to electric and magnetic fields. This is due to the fact that in nature there are electric charges, but no magnetic charges.
For stationary fields (E =const and B =const) Maxwell’s equations take the form:
E dl = 0; D dS = Q;
H dl = I; B dS = 0.
In this case, the electric and magnetic fields are independent of each other, which makes it possible to study the constant electric and magnetic fields separately.
Using the Stokes and Gauss theorems known from vector analysis:
A dl = rot A dS;
A dS = div A dV,
we can represent the complete system of Maxwell's equations in differential form:
rot E = - ¶ B/ ¶ t; div D = ρ;
rot H = j + ¶ D/ ¶ t; div B = 0.
If charges and currents are distributed continuously in space, then both forms of Maxwell's equations - integral and differential - are equivalent. However, when there are discontinuity surfaces - surfaces on which the properties of the medium or fields change abruptly, then the integral form of the equations is more general.
Maxwell's equations are the most general equations for electric and magnetic fields in media at rest. They play the same role in the doctrine of electromagnetism as Newton's laws in mechanics. From Maxwell's equations it follows that an alternating magnetic field is always associated with the electric field generated by it, and an alternating electric field is always associated with the magnetic field generated by it, i.e. Electric and magnetic fields are inextricably linked with each other - they form a single electromagnetic field.
Maxwell's theory is macroscopic, as it considers electric and magnetic fields created by macroscopic charges and currents. Therefore, this theory could not reveal the internal mechanism of phenomena that occur in the medium and lead to the emergence of electric and magnetic fields. A further development of Maxwell's theory of the electromagnetic field was Lorentz's electronic theory, and the Maxwell–Lorentz theory was further developed in quantum physics.
Maxwell's theory, being a generalization of the basic laws of electrical and magnetic phenomena, was able to explain not only already known experimental facts, which is also an important consequence of it, but also predicted new phenomena. One of the important conclusions of this theory was the existence of a magnetic field of displacement currents, the existence of electromagnetic waves - an alternating electromagnetic field propagating in space with a finite speed. Subsequently, it was proven that the speed of propagation of a free electromagnetic field (not bound by currents) in a vacuum is equal to the speed of light c = 3 · 10 8 m/s. This conclusion and theoretical study of the properties of electromagnetic waves led Maxwell to the creation of the electromagnetic theory of light, according to which light is also electromagnetic waves. Electromagnetic waves were experimentally obtained by G. Hertz (1857 – 1894), who proved that the laws of their excitation and propagation are completely described by Maxwell’s equations. Thus, Maxwell's theory received brilliant experimental confirmation.
Later, A. Einstein established that Galileo's principle of relativity for mechanical phenomena applies to all other physical phenomena.
According to Einstein's principle of relativity, mechanical, optical and electromagnetic phenomena occur in the same way in all inertial frames of reference, i.e. are described by the same equations. From this principle it follows that separate consideration of the electric and magnetic fields makes relative sense. So, if an electric field is created by a system of stationary charges, then these charges, being stationary relative to one inertial reference system, move relative to another and, therefore, will generate not only an electric, but also a magnetic field. Similarly, stationary relative to one inertial reference frame, a conductor with a constant current, exciting a constant magnetic field at each point in space, moves relative to other inertial frames, and the alternating magnetic field it creates excites a vortex electric field.
Thus, Maxwell's theory, its experimental confirmation, as well as Einstein's principle of relativity lead to a unified theory of electrical, magnetic and optical phenomena, based on the concept of an electromagnetic field.
Bibliography
P. S. Kudryavtsev. "Maxwell", M., 1976
D. MacDonald. "Faraday", Maxwell and Kelvin", M., 1967.
T. I. Trofimova. "Physics Course", M., 1983
G.M. Golin, S.R. Filonovich. Classics of physical science. "Graduate School". M., 1989.
Faraday's concept of lines of force was not taken seriously by other scientists for a long time. The fact is that Faraday, not having a sufficiently good command of the mathematical apparatus, did not provide a convincing justification for his conclusions in the language of formulas. (“It was a mind that never got bogged down in formulas,” A. Einstein said about him).
The brilliant mathematician and physicist James Maxwell defends Faraday's method, his ideas of short-range action and fields, arguing that Faraday's ideas can be expressed in the form of ordinary mathematical formulas, and these formulas are comparable to the formulas of professional mathematicians.
Field theory is developed by D. Maxwell in his works “On Physical Lines of Force” (1861-1865) and “Dynamic Field Theory (1864-1865). In the last work, a system of famous equations was given, which (according to Hertz) constitute the essence of Maxwell’s theory.
The gist of it was thata changing magnetic field creates not only in surrounding bodies, but also in a vacuum a vortex electric field, which, in turn, causes the appearance of a magnetic field. Thus, a new reality was introduced into physics - the electromagnetic field. This marked the beginning of a new stage in physics - a stage in which the electromagnetic field became a reality, material carrier of interaction.
The world began to appear as an electrodynamic system, built from electrically charged particles interacting through an electromagnetic field. (Indeed, let us remember that the MCM was dominated by the principle of long-range action, according to which the action of various kinds of forces is transmitted instantly, without the participation of the medium.)
The system of equations for electric and magnetic fields developed by Maxwell consists of 4 equations, which are equivalent to 4 statements.
Analyzing his equations, Maxwell came to the conclusion that electromagnetic waves must exist, and the speed of their propagation must be equal to the speed of light. Hence the conclusion: light is a type of electromagnetic waves. Based on his theory, Maxwell predicted the existence of pressure exerted by an electromagnetic wave, and, consequently, by light, which was brilliantly proven experimentally in 1906 by P.N. Lebedev.
The pinnacle of Maxwell's scientific work was his Treatise on Electricity and Magnetism.
Development of corpuscular-continuum concepts in the works of Maxwell. While developing the theory of the electromagnetic field, Maxwell did not reject the discrete nature of matter. He wrote: “Even an atom, when we attribute to it the ability to rotate, can be represented as consisting of many elementary particles.” This was said in 1873, long before the discovery of the electron. Thus, Maxwell did not give preference to either discreteness or continuity of matter, allowing for the possibility of both.
Having developed the EMCM, Maxwell completed the picture of the world of classical physics (“the beginning of the end of classical physics”). Maxwell's theory is the predecessor of Lorentz's electronic theory and A. Einstein's special theory of relativity.
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Topic: Electromagnetic induction
Lesson: Electromagneticfield.TheoryMaxwell
Let's consider the above diagram and the case when a direct current source is connected (Fig. 1).
Rice. 1. Scheme
The main elements of the circuit include a light bulb, an ordinary conductor, a capacitor - when the circuit is closed, a voltage appears on the capacitor plates equal to the voltage at the source terminals.
A capacitor consists of two parallel metal plates with a dielectric between them. When a potential difference is applied to the plates of a capacitor, they charge and an electrostatic field arises inside the dielectric. In this case, there cannot be any current inside the dielectric at low voltages.
When replacing direct current with alternating current, the properties of the dielectrics in the capacitor do not change, and there are still practically no free charges in the dielectric, but we observe that the light bulb is lit. The question arises: what is happening? Maxwell called the current arising in this case a displacement current.
We know that when a current-carrying circuit is placed in an alternating magnetic field, an induced emf appears in it. This is due to the fact that a vortex electric field arises.
What if a similar picture occurs when the electric field changes?
Maxwell's hypothesis: a time-varying electric field causes the appearance of a vortex magnetic field.
According to this hypothesis, a magnetic field after the circuit is closed is formed not only due to the flow of current in the conductor, but also due to the presence of an alternating electric field between the plates of the capacitor. This alternating electric field generates a magnetic field in the same area between the plates of the capacitor. Moreover, this magnetic field is exactly the same as if a current equal to the current in the rest of the circuit flowed between the plates of the capacitor. The theory is based on Maxwell's four equations, from which it follows that changes in electric and magnetic fields in space and time occur in a consistent manner. Thus, the electric and magnetic fields form a single whole. Electromagnetic waves propagate in space in the form of transverse waves with a finite speed.
The indicated relationship between the alternating magnetic and alternating electric fields suggests that they cannot exist separately from each other. The question arises: does this statement apply to static fields (electrostatic, created by constant charges, and magnetostatic, created by direct currents)? This relationship also exists for static fields. But it is important to understand that these fields can exist in relation to a certain frame of reference.
A charge at rest creates an electrostatic field in space (Fig. 2) relative to a certain reference system. It can move relative to other reference systems and, therefore, in these systems the same charge will create a magnetic field.
Electromagnetic field- this is a special form of existence of matter, which is created by charged bodies and is manifested by its action on charged bodies. During this action, their energy state can change, therefore, the electromagnetic field has energy.
1. The study of the phenomena of electromagnetic induction leads to the conclusion that an alternating magnetic field generates an electric vortex around itself.
2. Analyzing the passage of alternating current through circuits containing dielectrics, Maxwell came to the conclusion that an alternating electric field can generate a magnetic field due to a displacement current.
3. Electric and magnetic fields are components of a single electromagnetic field, which propagates in space in the form of transverse waves with a finite speed.
- Bukhovtsev B.B., Myakishev G.Ya., Charugin V.M. Physics 11th grade: Textbook. for general education institutions. - 17th ed., convert. and additional - M.: Education, 2008.
- Gendenstein L.E., Dick Yu.I., Physics 11. - M.: Mnemosyne.
- Tikhomirova S.A., Yarovsky B.M., Physics 11. - M.: Mnemosyne.
- Znate.ru ().
- Word ().
- Physics().
- What electric field is produced when the magnetic field changes?
- What current explains the glow of a light bulb in an alternating current circuit with a capacitor?
- Which of Maxwell's equations indicates the dependence of magnetic induction on conduction current and displacement?
Under certain conditions, alternating electric and magnetic fields can generate each other. They form an electromagnetic field, which is not their totality at all. This is a single whole in which these two fields cannot exist without each other.
From the history
The experiment of the Danish scientist Hans Christian Oersted, carried out in 1821, showed that electric current generates a magnetic field. In turn, a changing magnetic field can generate electric current. This was proven by the English physicist Michael Faraday, who discovered the phenomenon of electromagnetic induction in 1831. He is also the author of the term “electromagnetic field”.
At that time, Newton's concept of long-range action was accepted in physics. It was believed that all bodies act on each other through the void at an infinitely high speed (almost instantly) and at any distance. It was assumed that electric charges interact in a similar way. Faraday believed that emptiness does not exist in nature, and interaction occurs at a finite speed through a certain material medium. This medium for electric charges is electromagnetic field. And it travels at a speed equal to the speed of light.
Maxwell's theory
By combining the results of previous studies, English physicist James Clerk Maxwell created in 1864 electromagnetic field theory. According to it, a changing magnetic field generates a changing electric field, and an alternating electric field generates an alternating magnetic field. Of course, first one of the fields is created by a source of charges or currents. But in the future, these fields can already exist independently of such sources, causing each other to appear. That is, electric and magnetic fields are components of a single electromagnetic field. And every change in one of them causes the appearance of another. This hypothesis forms the basis of Maxwell's theory. The electric field generated by the magnetic field is a vortex. Its lines of force are closed.
This theory is phenomenological. This means that it is created based on assumptions and observations, and does not consider the cause of electric and magnetic fields.
Properties of the electromagnetic field
An electromagnetic field is a combination of electric and magnetic fields, therefore at each point in its space it is described by two main quantities: the electric field strength E and magnetic field induction IN .
Since the electromagnetic field is the process of converting an electric field into a magnetic field, and then magnetic into electric, its state is constantly changing. Propagating in space and time, it forms electromagnetic waves. Depending on the frequency and length, these waves are divided into radio waves, terahertz radiation, infrared radiation, visible light, ultraviolet radiation, x-rays and gamma rays.
The vectors of intensity and induction of the electromagnetic field are mutually perpendicular, and the plane in which they lie is perpendicular to the direction of propagation of the wave.
In the theory of long-range action, the speed of propagation of electromagnetic waves was considered infinitely large. However, Maxwell proved that this was not the case. In a substance, electromagnetic waves propagate at a finite speed, which depends on the dielectric and magnetic permeability of the substance. Therefore, Maxwell's Theory is called the theory of short-range action.
Maxwell's theory was experimentally confirmed in 1888 by the German physicist Heinrich Rudolf Hertz. He proved that electromagnetic waves exist. Moreover, he measured the speed of propagation of electromagnetic waves in a vacuum, which turned out to be equal to the speed of light.
In integral form, this law looks like this:
Gauss's law for magnetic field
The flux of magnetic induction through a closed surface is zero.
The physical meaning of this law is that magnetic charges do not exist in nature. The poles of a magnet cannot be separated. The magnetic field lines are closed.
Faraday's Law of Induction
A change in magnetic induction causes the appearance of a vortex electric field.
,
Magnetic field circulation theorem
This theorem describes the sources of the magnetic field, as well as the fields themselves created by them.
Electric current and changes in electrical induction generate a vortex magnetic field.
,
,
E– electric field strength;
N– magnetic field strength;
IN- magnetic induction. This is a vector quantity that shows the force with which the magnetic field acts on a charge of magnitude q moving with speed v;
D– electrical induction, or electrical displacement. It is a vector quantity equal to the sum of the intensity vector and the polarization vector. Polarization is caused by the displacement of electric charges under the influence of an external electric field relative to their position when there is no such field.
Δ - operator Nabla. The action of this operator on a specific field is called the rotor of this field.
Δ x E = rot E
ρ - density of external electric charge;
j- current density - a value showing the strength of the current flowing through a unit area;
With– speed of light in vacuum.
The study of the electromagnetic field is a science called electrodynamics. She considers its interaction with bodies that have an electric charge. This interaction is called electromagnetic. Classical electrodynamics describes only the continuous properties of the electromagnetic field using Maxwell's equations. Modern quantum electrodynamics believes that the electromagnetic field also has discrete (discontinuous) properties. And such electromagnetic interaction occurs with the help of indivisible particles-quanta that have no mass and charge. The electromagnetic field quantum is called photon .
Electromagnetic field around us
An electromagnetic field is formed around any conductor carrying alternating current. Sources of electromagnetic fields are power lines, electric motors, transformers, urban electric transport, railway transport, electrical and electronic household appliances - televisions, computers, refrigerators, irons, vacuum cleaners, radiotelephones, mobile phones, electric shavers - in short, everything related to consumption or transmission of electricity. Powerful sources of electromagnetic fields are television transmitters, antennas of cellular telephone stations, radar stations, microwave ovens, etc. And since there are quite a lot of such devices around us, electromagnetic fields surround us everywhere. These fields affect the environment and humans. This is not to say that this influence is always negative. Electric and magnetic fields have existed around humans for a long time, but the power of their radiation a few decades ago was hundreds of times lower than today.
Up to a certain level, electromagnetic radiation can be safe for humans. Thus, in medicine, low-intensity electromagnetic radiation is used to heal tissues, eliminate inflammatory processes, and have an analgesic effect. UHF devices relieve spasms of the smooth muscles of the intestines and stomach, improve metabolic processes in the body's cells, reducing capillary tone, and lower blood pressure.
But strong electromagnetic fields cause disruptions in the functioning of the human cardiovascular, immune, endocrine and nervous systems, and can cause insomnia, headaches, and stress. The danger is that their impact is almost invisible to humans, and disturbances occur gradually.
How can we protect ourselves from the electromagnetic radiation surrounding us? It is impossible to do this completely, so you need to try to minimize its impact. First of all, you need to arrange household appliances in such a way that they are located away from the places where we are most often. For example, don't sit too close to the TV. After all, the further the distance from the source of the electromagnetic field, the weaker it becomes. Very often we leave the device plugged in. But the electromagnetic field disappears only when the device is disconnected from the electrical network.
Human health is also affected by natural electromagnetic fields - cosmic radiation, the Earth’s magnetic field.
Faraday's concept of lines of force was not taken seriously by other scientists for a long time. The fact is that Faraday, not having a sufficiently good command of the mathematical apparatus, did not provide a convincing justification for his conclusions in the language of formulas. (“He was a mind that never got bogged down in formulas,” A. Einstein said about him).
The brilliant mathematician and physicist James Maxwell defends Faraday's method, his ideas of short-range action and fields, arguing that Faraday's ideas can be expressed in the form of ordinary mathematical formulas, and these formulas are comparable to the formulas of professional mathematicians.
D. Maxwell develops field theory in his works “On Physical Lines of Force” (1861-1865) and “Dynamic Field Theory” (1864-1865). In the last work, a system of famous equations was given, which, according to G. Hertz, constitute the essence of Maxwell’s theory.
This essence boiled down to the fact that a changing magnetic field creates not only in surrounding bodies, but also in a vacuum a vortex electric field, which, in turn, causes the appearance of a magnetic field. Thus, a new reality was introduced into physics - the electromagnetic field. This marked the beginning of a new stage in physics, a stage in which the electromagnetic field became a reality, a material carrier of interaction.
The world began to appear as an electrodynamic system, built from electrically charged particles interacting through an electromagnetic field.
The system of equations for electric and magnetic fields developed by Maxwell consists of 4 equations that are equivalent to four statements:
Analyzing his equations, Maxwell came to the conclusion that electromagnetic waves must exist, and the speed of their propagation must be equal to the speed of light. This led to the conclusion that light is a type of electromagnetic wave. Based on his theory, Maxwell predicted the existence of pressure exerted by an electromagnetic wave, and, consequently, by light, which was brilliantly proven experimentally in 1906 by P.N. Lebedev.
The pinnacle of Maxwell's scientific work was his Treatise on Electricity and Magnetism.
Having developed the electromagnetic picture of the world, Maxwell completed the picture of the world of classical physics (“the beginning of the end of classical physics”). Maxwell's theory is the predecessor of Lorentz's electronic theory and A. Einstein's special theory of relativity.
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