The electric field that occurs when the magnetic field changes has a completely different structure than the electrostatic one. It is not directly related to electric charges, and its lines of tension cannot begin and end on them. They generally do not begin or end anywhere, but are closed lines, similar to the lines of induction of a magnetic field. This is the so-called vortex electric field. The question may arise: why, in fact, is this field called electric? After all, it has a different origin and a different configuration than a static electric field. The answer is simple: the vortex field acts on the charge qin the same way as electrostatic, and this we considered and still consider the main property of the field. The force acting on the charge is still F= qE,where E- intensity of the vortex field.
If the magnetic flux is created by a uniform magnetic field concentrated in a long narrow cylindrical tube of radius r 0 (Fig.5.8), then from considerations of symmetry it is obvious that the lines of electric field strength lie in planes perpendicular to the lines B, and are circles. In accordance with Lenz's rule, with increasing magnetic
induction of the line of tension E form a left screw with the direction of the magnetic induction B.
Unlike a static or stationary electric field, the work of the vortex field on a closed path is not zero. Indeed, when the charge moves along the closed line of the electric field strength, the work on all sections of the path has the same sign, since the force and movement coincide in direction. A vortex electric field, like a magnetic field, is not potential.
The work of a vortex electric field on the movement of a single positive charge along a closed fixed conductor is numerically equal to the EMF of induction in this conductor.
If an alternating current flows through the coil, then the magnetic flux penetrating the coil changes. Therefore, an EMF of induction appears in the same conductor through which the alternating current flows. This phenomenon is called self-induction.
In self-induction, the conducting circuit plays a double role: a current flows through it, causing induction, and the EMF of induction appears in it. The changing magnetic field induces an EMF in the very conductor through which the current flows, which creates this field.
At the moment of current rise, the intensity of the vortex electric field, in accordance with Lenz's rule, is directed against the current. Consequently, at this moment, the vortex field prevents the growth of the current. On the contrary, when the current decreases, the vortex field maintains it.
This leads to the fact that when a circuit containing a source of constant EMF is closed, a certain value of the current strength is not established immediately, but gradually over time (Fig.5.13). On the other hand, when the source is turned off, the current in closed circuits does not stop instantly. The EMF of self-induction arising in this case can exceed the EMF of the source, since the change in the current and its magnetic field when the source is turned off occurs very quickly.
The phenomenon of self-induction can be observed in simple experiments. Figure 5.14 shows a diagram of parallel connection of two identical lamps. One of them is connected to the source through a resistor R,and the other in series with the coil Lwith an iron core. When the key is closed, the first lamp flashes almost immediately, and the second - with a noticeable delay. The self-induction EMF in the circuit of this lamp is large, and the current strength does not immediately reach its maximum value. The emergence of an EMF of self-induction when opening can be observed experimentally with a circuit schematically shown in Figure 5.15. When opening the key in the coil LeMF of self-induction arises, maintaining the initial current. As a result, at the moment of opening, a current flows through the galvanometer (dashed arrow) directed against the initial current before opening (solid arrow). Moreover, the current when the circuit is opened exceeds the current passing through the galvanometer when the switch is closed. This means that the EMF of self-induction ξ.
more EMF ξ isbattery cells.
The phenomenon of self-induction is similar to the phenomenon of inertia in mechanics. So, inertia leads to the fact that under the action of force, the body does not instantly acquire a certain speed, but gradually. The body cannot be instantly slowed down, no matter how great the braking force is. In the same way, due to self-induction when the circuit is closed, the current strength does not immediately acquire a certain value, but increases gradually. Turning off the source, we do not stop the current immediately. Self-induction maintains it for some time, despite the presence of circuit resistance.
Further, in order to increase the speed of the body, according to the laws of mechanics, you need to do work. When braking, the body itself performs positive work. In the same way, to create a current, it is necessary to do work against the vortex electric field, and when the current disappears, this field itself performs positive work.
This is not just an external analogy. It has a deep inner meaning. After all, current is a collection of moving charged particles. With an increase in the speed of electrons, the magnetic field created by them changes and generates a vortex electric field, which acts on the electrons themselves, preventing an instant increase in their speed under the action of an external force. On deceleration, on the contrary, the vortex field tends to maintain the electron velocity constant (Lenz's rule). Thus, the inertness of electrons, and hence their mass, at least in part, is of electromagnetic origin. Mass cannot be completely electromagnetic, since there are electrically neutral particles with mass (neutrons, etc.)
Inductance.
Modulus B of the magnetic induction created by the current in any closed loop is proportional to the current strength. Since the magnetic flux Ф is proportional to В, then Ф ~ В ~ I.
It can therefore be argued that
where L- the coefficient of proportionality between the current in the conducting circuit and the magnetic flux created by it, penetrating this circuit. The quantity Lcalled the inductance of the circuit or its self-induction coefficient.
Using the law of electromagnetic induction and expression (5.7.1), we obtain the equality:
| (5.7.2) |
From formula (5.7.2) it follows that inductance- it is a physical quantity, numerically equal to the EMF of self-induction arising in the circuit when the current strength changes by 1 A per1 sec.
Inductance, like electrical capacity, depends on geometric factors: the size of the conductor and its shape, but does not directly depend on the current in the conductor. Besides
the geometry of the conductor, the inductance depends on the magnetic properties of the medium in which the conductor is located.
The SI unit of inductance is called henry (H). The inductance of the conductor is1 Gn, if in it when the current strength changes by1 A per1s eMF of self-induction occurs1 B:
Another special case of electromagnetic induction is mutual induction. Mutual induction is called the occurrence of an induction current in a closed loop(reel) when the current strength in the adjacent circuit changes(coil). In this case, the contours are stationary relative to each other, such as, for example, the coils of a transformer.
Quantitatively, mutual induction is characterized by the coefficient of mutual induction, or mutual inductance.
Figure 5.16 shows two contours. When changing the current I 1 in the circuit 1 in the loop 2 induction current I 2 appears.
The flux of magnetic induction Ф 1.2, created by the current in the first circuit and penetrating the surface bounded by the second circuit, is proportional to the current I 1:
The coefficient of proportionality L 1, 2 is called mutual inductance. It is similar to inductance L.
EMF of induction in the second circuit, according to the law of electromagnetic induction, is equal to:
The coefficient L 1.2 is determined by the geometry of both circuits, the distance between them, their relative position and the magnetic properties of the environment. Mutual inductance is expressed L 1,2, like inductance L, in henry.
If the current strength changes in the second circuit, then the EMF of induction appears in the first circuit
When the current strength in the conductor changes, a vortex electric field arises in the latter. This field slows down electrons with increasing current strength and accelerates with decreasing.
Energy of the magnetic field of the current.
When a circuit containing a source of constant EMF is closed, the energy of the current source is initially spent on creating a current, that is, on setting in motion the electrons of the conductor and the formation of a magnetic field associated with the current, as well as partly on increasing the internal energy of the conductor, that is, on heating it. After a constant value of the current strength is established, the energy of the source is spent exclusively on the release of heat. In this case, the current energy does not change.
To create a current, it is necessary to expend energy, that is, it is necessary to perform work. This is explained by the fact that when the circuit is closed, when the current begins to increase, a vortex electric field appears in the conductor, acting against the electric field that is created in the conductor due to the current source. In order for the current to become equal to I, the current source must do work against the forces of the vortex field. This work is used to increase the energy of the current. The vortex field does negative work.
When the circuit is opened, the current disappears and the vortex field does positive work. The energy stored by the current is released. This is detected by a powerful spark that occurs when a high inductance circuit is opened.
The expression for the energy of the current I flowing through the circuit with inductance L can be written based on the analogy between inertia and self-induction.
If self-induction is similar to inertia, then inductance in the process of creating a current should play the same role as mass with an increase in the speed of a body in mechanics. The role of the speed of a body in electrodynamics is played by the current strength I as a quantity characterizing the movement of electric charges. If so, then the energy of the current W m can be considered a quantity similar to the kinetic energy of the body - in mechanics, and write it down as.
The cause of the occurrence of electric current in a fixed conductor is an electric field. Any change in the magnetic field generates an induction electric field regardless of the presence or absence of a closed loop, while if the conductor is open, then a potential difference arises at its ends; if the conductor is closed, then an induction current is observed in it.
The induction electric field is vortex. The direction of the lines of force of the vortex el. field coincides with the direction of the induction current. An induction electric field has completely different properties in contrast to an electrostatic field.
|
electrostatic field |
induction electric field (vortex electric field) |
|
1. created by motionless electr. charges |
1.Caused by changes in the magnetic field |
|
2.the field lines are open - -potential field |
2. the lines of force are closed - - vortex field |
|
3. field sources are electr. charges |
3.field sources cannot be specified |
|
4. work of the field forces to move the test charge along a closed path \u003d 0. |
4.the work of the field forces to move the test charge along a closed path \u003d EMF of induction |
Eddy currents
Induction currents in massive conductors are called Foucault currents. Foucault currents can reach very high values, because the resistance of massive conductors is low; therefore, transformer cores are made of insulated plates. Eddy currents practically do not arise in ferrites - magnetic insulators.
Using eddy currents
Heating and melting of metals in vacuum, dampers in electrical measuring instruments.
The harmful effects of eddy currents
These are energy losses in the cores of transformers and generators due to the release of a large amount of heat.
SELF-INDUCTION
Each conductor through which current flows is in its own magnetic field.
When the current in the conductor changes, the m.field changes, i.e. the magnetic flux created by this current changes. A change in the magnetic flux leads to the emergence of a vortex electric field and an EMF of induction appears in the circuit. 
This phenomenon is called self-induction. Self-induction is the phenomenon of induction EMF in an electric circuit as a result of a change in current strength. The resulting EMF is called the EMF of self-induction
The manifestation of the phenomenon of self-induction
Closing the circuit 
When closed in the electric circuit, the current increases, which causes an increase in the magnetic flux in the coil, a vortex electric field appears, directed against the current, i.e. EMF of self-induction arises in the coil, which prevents the growth of current in the circuit (the vortex field slows down the electrons). As a result L1 lights up later than L2.
Open circuit 
When the electric circuit is opened, the current decreases, a decrease in the flow rate in the coil occurs, a vortex electric field appears, directed like a current (tending to maintain the same current strength), i.e. EMF of self-induction appears in the coil, which maintains the current in the circuit. As a result, when switching off
flashes brightly. Conclusion in electrical engineering, the phenomenon of self-induction manifests itself when the circuit is closed (the electric current increases gradually) and when the circuit is opened (the electric current does not disappear immediately).
INDUCTANCE
What does the EMF of self-induction depend on? Electric current creates its own magnetic field. The magnetic flux through the circuit is proportional to the magnetic field induction (F ~ B), the induction is proportional to the current in the conductor (B ~ I), therefore the magnetic flux is proportional to the current (F ~ I). The EMF of self-induction depends on the rate of change in the current in the electric circuit, on the properties of the conductor (size and shape) and on the relative magnetic permeability of the medium in which the conductor is located. The physical quantity that shows the dependence of the EMF of self-induction on the size and shape of the conductor and on the environment in which the conductor is located is called the self-induction coefficient or inductance. 
Inductance - physical a value numerically equal to the EMF of self-induction arising in the circuit when the current strength changes by 1 Ampere in 1 second. Also inductance can be calculated using the formula:
where Ф is the magnetic flux through the circuit, I is the current in the circuit.
SI units of inductance:
The inductance of the coil depends on: the number of turns, the size and shape of the coil and the relative magnetic permeability of the medium (possibly a core).
EMF OF SELF-INDUCTION
The self-induction EMF prevents the increase in current when the circuit is turned on and the decrease in the current when the circuit is opened.
Physics is the most computerized subject among all academic disciplines. Information technology can be used to study theoretical material, training, as a means of modeling and visualization, etc. The choice depends on the goals, objectives and stage of the lesson (explanation, consolidation, repetition of material, knowledge testing, etc.).
Teaching children physics, we observe a decrease in interest in the subject, and with this a decrease in the level of knowledge. I explained this problem by the lack of visual material, the lack of equipment, the complexity of the object itself. The problems that have arisen are associated with the rapidly and continuously growing volume of human knowledge. With the volume of information doubling every few years, the classic textbook and teacher inevitably become providers of outdated knowledge. But I also noted that the number of children who can use a computer is growing rapidly, and this trend will accelerate regardless of the school paradigm. For me, the question arose, why not use the new pedagogical capabilities of the computer as a teaching tool.
A computer for students - as a source of new information and as a tool for intellectual and, in general, cognitive activity. Working on a computer can (and should) also develop such personal qualities as reflexivity, criticality to information, responsibility, the ability to make independent decisions, and finally, tolerance and creativity, and communication skills.
A computer for a teacher is a modern means of solving didactic problems of organizing new forms of developmental education.
Note the general importance of computers in the educational process... They:
Fits into the framework of traditional education.
They are used with success in educational and extracurricular activities of various content and organization.
Promote the active involvement of the student in the educational process, maintain interest.
Computer didactic features:
Information saturation.
The ability to overcome existing temporal and spatial boundaries.
The possibility of deep penetration into the essence of the studied phenomena and processes.
Demonstration of the studied phenomena in development, dynamics.
Reality display of reality.
Expressiveness, richness of expressive techniques, emotional richness.
Such a wealth of capabilities of the computer allows you to take a closer look at studying it as a new didactic tool.
When conducting physics lessons, the following types of ICT:
multimedia presentations,
videos and video clips,
animations simulating physical processes,
electronic textbooks,
training programs,
simulator programs (to prepare for the exam),
work with internet sites
physical laboratory L-micro.
When delivering lessons, the most common form of ICT application is multimedia presentation. This kind of lesson support allows you to focus on the most important elements of the material being studied, to include animations and video fragments. In addition, multimedia presentations are used by students when making reports and presentations or when defending research papers. When preparing a presentation for a lesson, the following features must be considered:
the presentation should be clear, the slide should not contain a lot of text, the text should be large and easy to read;
the presentation must be illustrated: contain drawings, photographs, diagrams;
the number of slides should be limited (15-20 slides);
the presentation should not cause discomfort caused by dynamic playback and changing frames, or color discomfort;
the most important information should be placed on the first and last slides.
When creating a presentation, remember that it is an accompaniment to a speech, report, or lesson, and does not replace it. Often, when making presentations, students try to place all the information in it; the teacher's role in this situation is to correct the content of the presentation and its perception. This is most relevant when defending projects, competition and research works. In all competitions, when evaluating the work, visibility is taken into account, which for the most part is a multimedia presentation.
Another type of ICT used in teaching physics is the use of electronic aids. It is more expedient to use electronic textbooks and training programs when doing homework and independent work of students, as well as when working with any educational literature, in this case it is necessary to carefully think over and concretize tasks for students.
Simulator programs act as an independent product that allows you to work out the studied material, to identify the problems that students face when studying theoretical material.
Online tests play a special role in preparing for the state final certification. The student sees the result almost immediately and realistically evaluates his capabilities.
An important element of the use of ICT in teaching physics is working with interactive models, which are presented in products such as "Live Physics", "Open Physics". Almost all models allow you to show experiments when explaining new material. Working with this kind of programs allows you to look deep into the phenomenon, to consider processes that cannot be observed in a "live" experiment. When using models for demonstrations, it is possible to attract one of the students as an assistant, since it is quite difficult to work at the computer and at the same time give the necessary explanations to the class. In addition, independent work of students with these programs contributes to the development of cognitive activity.
Of particular interest among students is the conduct of virtual laboratory work in physics lessons. Students can set up the necessary computer experiments to test their own considerations when answering questions or solving problems. Of course, a computer laboratory cannot replace a real physics laboratory. Nevertheless, the implementation of computer laboratory work requires certain skills that are characteristic of a real experiment - the choice of initial conditions, setting the parameters of the experiment, etc.
The L-micro physics laboratory plays a key role in teaching physics. The use of a computer as a measuring tool allows you to expand the boundaries of a school physical experiment and conduct physical research.
When preparing for physics lessons, it is necessary to remember the rapid development of science and technology. Possessing new information about the achievements of modern physics in a particular area, the teacher not only emphasizes the relevance and necessity of studying physics in school, but also develops the cognitive activity of the student. At the same time, it is advisable to instruct students to search for information about modern achievements in this field of physics. As a rule, schoolchildren are creative in the search process and often, being carried away by the collection of information, are carried away by the problem itself, which can develop into independent research. However, schoolchildren should be drawn to the search for reliable sources of information. One of such Internet sources is the popular site about fundamental science elementy.ru.
The website can be not only a source of information, but also an independent educational product. So the site elementy.ru, in addition to informational sections, also contains interactive posters, when working with which students have the opportunity not only to see the diagrams of the most complex technical devices, but also to "look" inside, change the working conditions and study the theoretical foundations of the processes. Working with such posters allows you to show the practical significance of the laws studied in physics lessons.
By including ICT elements in the process of teaching physics, the teacher not only develops the cognitive activity of students, but also improves himself. For the active use of ICT in the classroom, the teacher needs to master certain skills:
to process text, digital, graphic and sound information with the help of appropriate editors for the preparation of didactic materials;
create slides on this training material using the presentation editor (MS PowerPoint), demonstrate a presentation in the lesson;
use available off-the-shelf software products in your discipline;
organize work with an electronic textbook in the classroom;
search for information on the Internet in preparation for lessons and extracurricular activities;
organize work with students to find the necessary information in the global network directly in the classroom;
work in the lesson with materials from websites.
In conclusion, I note that in modern conditions there is a pedagogical task to resist the excessive introduction of ICT in the process of teaching physics, so that colorful illustrations and models do not overshadow the true experimental nature of physical science, do not forget the "live" experiment.
Solenoidal vector field
Definition
The vector field is called solenoidal or vortexif through any closed surface S its flow is zero:
∫ S a → ⋅ d s → \u003d 0 (\\ displaystyle \\ int \\ limits _ (S) (\\ vec (a)) \\ cdot (\\ vec (ds)) \u003d 0).
If this condition is satisfied for any closed S in some region (by default - everywhere), then this condition is equivalent to the fact that the divergence of the vector field a → (\\ displaystyle (\\ vec (a))) is equal to zero:
D i v a → ≡ ∇ ⋅ a → \u003d 0 (\\ displaystyle \\ mathrm (div) \\, (\\ vec (a)) \\ equiv \\ nabla \\ cdot (\\ vec (a)) \u003d 0)
everywhere in this area (it is assumed that divergence exists everywhere in this area). Therefore, solenoidal fields are also called divergent .
For a wide class of domains, this condition is satisfied if and only if a → (\\ displaystyle (\\ vec (a))) has a vector potential, that is, there is some such vector field A → (\\ displaystyle (\\ vec (A))) (vector potential) such that a → (\\ displaystyle (\\ vec (a))) can be expressed as its rotor:
A → \u003d ∇ × A → ≡ r o t A →. (\\ displaystyle (\\ vec (a)) \u003d \\ nabla \\ times (\\ vec (A)) \\ equiv \\ mathrm (rot) \\, (\\ vec (A)).)
In other words, a field is vortex if it has no sources. The lines of force of such a field have no beginning or end, and are closed. The vortex field is generated not by resting charges (sources), but by a change in the associated field (for example, for an electric field, it is generated by a change in the magnetic field). Since there are no magnetic charges in nature, the magnetic field is always is vortex, and its lines of force are always closed. The lines of force of a permanent magnet, despite the fact that they go out of its poles (as if they have sources inside), in fact are closed inside the magnet. Therefore, by cutting the magnet in two, it will not be possible to obtain two separate magnetic poles.
Examples of
- Field of the magnetic induction vector (follows from Maxwell's equations, and more specifically from Gauss's theorem for a magnetic field).
- The velocity field of an incompressible fluid (follows from the continuity equation at ∂ ρ / ∂ t \u003d 0 (\\ displaystyle \\ partial \\ rho / \\ partial t \u003d 0)).
- Electric field in areas where there are no sources (charges). For solenoid field E the absence (or mutual compensation) of free and bound charges is necessary. For solenoid D the absence of only free charges is sufficient.
- The field of the current density vector is solenoidal in the absence of a change in the charge density with time (then the solenoidal current density follows from the continuity equation).
Etymology
Word solenoidal comes from Greek solenoid (σωληνοειδές, sōlēnoeidēs) meaning "pipelike" or "like in a pipe" containing the word σωλην (Solen) - trumpet... In this context, this means fixing the volume for the flowing fluid model, the absence of sources and sinks (as in the case of flow in a pipe, where new fluid does not appear or disappear).
Installation Description
In this work, the following devices are used (see Fig. 13.1, b and 13.2, and): neon lamp N; source of power U 0; voltmeter V; ammeter AND; an oscilloscope used to observe the form of relaxation oscillations and measure the signal parameters.
The task
1. Assemble the circuit according to fig.13.1, in... By changing U 0, remove the forward and reverse branches of the I - V characteristic of the neon lamp. Define U s and U d. Rate R i a burning lamp at two experimental points.
2. Assemble the circuit according to fig.13.2, and... Get a stable picture of relaxation oscillations on the oscilloscope screen and sketch it in a work log.
3. Measure the vibration amplitude with an oscilloscope.
4. Investigate the dependence of the oscillation period T from the parameters of the circuit:
a) remove addiction T from R with fixed U 0 = U 01 and C= C 1 ;
b) remove addiction T from C with fixed U 0 = U 01 and R= R 1 .
5. Use the assembled relaxation generator as a sweep generator, for which switch the oscilloscope into two-channel operation mode " X – Y»And send a sinusoidal signal from the GSK generator to the second channel. Having chosen the frequency of the sinusoidal signal of the GSK, get a stable picture on the oscilloscope screen and sketch it in the laboratory journal. After turning off the relaxation generator, apply the same GSK signal to the first channel of the oscilloscope and, turning on the sweep generator, get a stable picture of the signal sweep on the screen, sketch it in the laboratory journal. Explain the qualitative difference between pictures.
6. Plot the I - V characteristic of a neon lamp. Determine the internal resistance of a burning neon lamp according to the schedule R i = = dU/dI for Uslightly less than U h.
7. Build dependency graphs T= T(R),T= T(C). On the same graphs, construct theoretical dependencies using formula (13.2).
test questions
1. What are relaxation vibrations?
2. Tell us about the features of the current-voltage characteristics of a neon lamp.
3. What is the internal resistance of the lamp and how to find it by the current-voltage characteristic?
4. Output formula (13.1).
5. Explain the principle of operation of the relaxation generator shown in Fig. 13.2, and.
6. What form do relaxation oscillations have in this work?
7. What should be the ratio between the resistance and the internal resistance of a burning and non-burning neon lamp in order for the oscillation period to be determined by formula (13.2)?
8. How can the oscillation period be changed?
9. How can the vibration amplitude be changed?
10. What are the reasons for choosing U in the generator?
11. What is the waveform of the oscilloscope sweep generator? Can a relaxation generator be used as a sweep generator? How is the shape of the signal under investigation distorted in this case and why?
Work 14 vortex electric field
Purpose: study of the properties of the vortex electric field.
Introduction
It follows from Maxwell's equations that a magnetic field that changes over time generates an electric one. The corresponding equation is written as
, (14.1)
where E is the vector of the electric field strength, B is the vector of magnetic induction. The same equation in integral form as applied to a solenoid using a cylindrical coordinate system looks like this:
, (14.2)
where 
- the circumferential component of the electric field strength; 
is the axial component of the magnetic induction, and the integrals are taken along a closed loop l and on the surface Sbased on this contour.
The work uses a vortex electric field of a solenoid, through which an alternating electric current flows. The vortex electric field is measured in a cross section perpendicular to the solenoid axis and passing through its middle. The length of the solenoid is significantly larger than its diameter, therefore, in the first approximation, we can assume that we are dealing with an infinitely long solenoid.
It is known that the magnetic field inside an infinite solenoid is uniform and its magnetic induction is determined by the formula:
, (14.3)
where is the relative magnetic permeability of the substance (for air \u003d 1.0000004); 0 \u003d 1.26 · 10–6 H / m - magnetic constant; n - the number of turns of the solenoid per unit of its length, I - current strength in the solenoid (a quasi-stationary current is considered). Outside the solenoid, the magnetic induction is negligible.
Equation (14.2) is greatly simplified if the surface S take a circle with a radius r, the center of which is on the axis of the solenoid and the plane is perpendicular to this axis. In this case Lis a circle with a radius r. Since the quantity B z / t is homogeneous inside an infinite solenoid and practically equal to zero outside it, then the right integral is:
where R- solenoid radius.
The integral on the left-hand side of Eq. (14.2) due to the axial symmetry of the problem is E 2 r... As a result, after simple transformations, we obtain the following expression for the modulus of the vortex electric field:
(14.4)
Since B z / t does not depend on r, then the intensity of the vortex electric field is proportional to the distance r from the solenoid axis at r< R and inversely proportional r at r R.
In the case when the solenoid current changes according to a sinusoidal law
Physics definition
A vortex electric field is
Ksyulenok haveleva
VORTEX ELECTRIC FIELD
The cause of the electric current in a stationary conductor is an electric field.
Any change in the magnetic field generates an induction electric field, regardless of the presence or absence of a closed loop,
in this case, if the conductor is open, then a potential difference arises at its ends;
if the conductor is closed, then an induction current is observed in it. The induction electric field is vortex.
The direction of the lines of force of the vortex el. field coincides with the direction of the induction current
An induction electric field has completely different properties in contrast
from the electrostatic field.
Using eddy currents: heating and melting metals in vacuum;
dampers in electrical measuring instruments.
The harmful effects of eddy currents: energy losses in the cores of transformers and generators
due to the generation of a large amount of heat.
1. Forces of interaction between molecules and atoms in bodies
(slide \u003d Answer)
The forces of attraction and repulsion, called molecular forces, act simultaneously between molecules. These are forces of an electromagnetic nature. The forces acting between two molecules depend on the distance between them. If the distance between molecules is increased, the forces of intermolecular attraction prevail. At small distances, repulsive forces prevail.
2. What determines the rate of diffusion, evaporation, Brownian motion
(slide \u003d Answer)
The diffusion rate depends on the type of substance, on temperature, on the state of aggregation of the substance.
The speed of the Brownian motion depends on the temperature and the mass of the Brownian particle.
Evaporation rate depends on the type of substance, temperature, surface area, the presence of air movement above the surface (wind)
3. Instruments for measuring temperature, pressure, humidity
(slide \u003d Answer)
A thermometer is used to measure the temperature.
A pressure gauge is used to measure pressure.
To measure humidity, a condensation hygrometer, a hair hygrometer, and a psychrometer are used.
4. Phase transitions (vaporization, melting, sublimation, condensation, crystallization)
(slide \u003d Answer)
Melting is the process of transition of a substance from a solid to a liquid state.
Crystallization is the process of transition of a substance from a liquid to a solid state.
Sublimation is the process of transition of a substance from a solid to a gaseous state.
Vaporization is the process of transition of a substance from a liquid to a gaseous state.
Condensation is the process of transition of a substance from a gaseous state to a liquid state.
5. Saturated, unsaturated steam, dynamic equilibrium
(slide \u003d Answer)
Saturated steam is steam that is in dynamic equilibrium with its liquid.
Unsaturated steam - steam that has not reached dynamic equilibrium with its liquid.
Dynamic equilibrium is a state between a liquid and its vapor in which the number of molecules leaving the liquid is equal to the number of molecules returning to it.
6. Formulas of gas pressure, Klaiperon equation, Mendeleev-Klaiperon equation, relationship of kinetic energy with temperature
(slide \u003d Answer)
Gas pressure formula - combined gas law - p = nkT
Cliperon's equation
The Mendeleev-Cliperon equation
Relationship of kinetic energy with temperature E \u003d (3/2) kT
7. Conversion of temperature from Celsius to Kelvin, from Kelvin to Celsius
(slide \u003d Answer)
Relation between absolute temperature and temperature on a scale Celsiusexpressed by the formula T \u003d 273.16 +t where t is the temperature in degrees Celsius.
The approximate formula is used more often:
1) to convert from temperature in Celsius to temperature in Kelvin T \u003d 273 + t
2) to convert from temperature in Kelvin to temperature in Celsius t \u003d T - 273
8. Kelvin scale, Celsius scale
(slide \u003d Answer)
0 0 Celsius - ice melting temperature.
100 0 on the Kelvin scale is the boiling point of water.
0 0 on the Kelvini scale - absolute zero - the temperature at which the translational motion of molecules should stop.
celsius scale Kelvin scale
9. Relationship between temperature and pressure of gas, between temperature and kinetic energy of gas molecules
(slide \u003d Answer)
The relationship between temperature and gas pressure p \u003d nkT. Between p and T there is a direct proportional relationship(the number of times the temperature increases, the same number of times the gas pressure increases).
The relationship between temperature and kinetic energy of gas molecules is Е \u003d (3/2) kТ. Between p and E there is a direct proportional relationship (how many times the temperature increases, the kinetic energy of gas molecules also increases by the same factor)
10. The main provisions of the ICB and their experimental justification
(slide \u003d Answer)
The MKT is based on three important principles, confirmed experimentally and theoretically.
- All bodies are composed of the smallest particles - atoms, molecules, which include even smaller elementary particles (electrons, protons, neutrons). The structure of any substance is discrete (discontinuous).
- Atoms and molecules of matter are always in continuous chaotic motion.
- There are forces of interaction between the particles of any substance - attraction and repulsion. The nature of these forces is electromagnetic.
These provisions are confirmed empirically.
11. Mass and size of molecules
(slide \u003d Answer)
Moleculeis called the smallest stable particle of a given substance, which has its basic chemical properties.
A molecule is made up of even smaller particles - atoms, which in turn are made up of electrons and nuclei.
Atomis called the smallest particle of a given chemical element.
The molecules are very small.
The order of magnitude of the diameter of a molecule is 1 · 10 -8 cm \u003d 1 * 10-10 m
The order of magnitude of the volume of a molecule is 1 · 10 -20 m3
Order of magnitude of molecular mass1 · 10 - 23 g \u003d 1 · 10 -26 kg
12. Properties of solids, liquids, gases
(slide \u003d Answer)
Solids retain their volume, retain their shape.
Liquids retain their volume, do not retain their shape.
Gases do not retain volume, do not retain their shape.
13. Phase transitions occur with absorption or release of heat.
(slide \u003d Answer)
Melting occurs with heat absorption
Crystallization occurs with the release of heat.
Vaporization occurs with heat absorption.
Condensation occurs with the release of heat.
Sublimation occurs with heat absorption
14. Air humidity and dew point
(slide \u003d Answer)
Absolute humidity– a value showing what mass of water vapor is in 1 m³ of air.
Relative humidity -it is a value indicating how far the steam is from saturation. This is the partial pressure ratiop of water vapor contained in air at a given temperature, to saturated steam pressure p 0 at the same temperature, expressed as a percentage:
If the air does not contain water vapor, then its absolute and relative humidity are equal to 0.
If the humid air is cooled, then the steam in it can be brought to saturation, and then it will condense.
Dew point -it is the temperature at which water vapor in the air becomes saturated.
15. Melting and boiling graph
How does the electromotive force arise in a conductor that is in an alternating magnetic field? What is a vortex electric field, its nature and causes of occurrence? What are the main properties of this field? Today's lesson will answer all these and many other questions.
Topic: Electromagnetic induction
Lesson:Vortex electric field
Recall that Lenz's rule allows you to determine the direction of the induction current in a circuit located in an external magnetic field with a variable flux. Based on this rule, it was possible to formulate the law of electromagnetic induction.
The law of electromagnetic induction
When the magnetic flux penetrating the area of \u200b\u200bthe circuit changes, an electromotive force arises in this circuit, numerically equal to the rate of change of the magnetic flux, taken with a minus sign.
How does this electromotive force arise? It turns out that the EMF in a conductor, which is in an alternating magnetic field, is associated with the emergence of a new object - vortex electric field.
Consider experience. There is a coil of copper wire, into which an iron core is inserted in order to increase the magnetic field of the coil. The coil is connected to an alternating current source through conductors. There is also a coil of wire placed on a wooden base. An electric bulb is connected to this loop. The wire material is covered with insulation. The base of the coil is made of wood, that is, a non-conductive material. The coil frame is also made of wood. Thus, any possibility of contact of a light bulb with a circuit connected to a current source is excluded. When the source is closed, the lamp lights up, therefore, an electric current flows in the loop, which means that external forces in this loop are doing work. It is necessary to find out where the outside forces come from.
The magnetic field penetrating the plane of the loop cannot cause the appearance of an electric field, since the magnetic field acts only on moving charges. According to the electronic theory of conduction of metals, electrons exist inside them, which can move freely within the crystal lattice. However, this movement in the absence of an external electric field is chaotic. This disorder leads to the fact that the total effect of the magnetic field on the conductor with current is zero. This is how the electromagnetic field differs from the electrostatic field, which also acts on stationary charges. So, the electric field acts on moving and stationary charges. However, the kind of electric field that was studied earlier is created only by electric charges. Induction current, in turn, is created by an alternating magnetic field.
Suppose that the electrons in a conductor come into orderly motion under the influence of some new kind of electric field. And this electric field is generated not by electric charges, but by an alternating magnetic field. Faraday and Maxwell came up with a similar idea. The main thing in this idea is that a time-varying magnetic field generates an electric one. A conductor with free electrons in it allows you to detect this field. This electric field sets in motion the electrons in the conductor. The phenomenon of electromagnetic induction consists not so much in the appearance of an inductive current, but in the appearance of a new kind of electric field, which sets in motion electric charges in a conductor (Fig. 1).
The vortex field is different from the static one. It is not generated by stationary charges, therefore, the intensity lines of this field cannot begin and end on a charge. According to research, the vortex field strength lines are closed lines, similar to the magnetic induction lines. Therefore, this electric field is vortex - the same as the magnetic field.
The second property concerns the workings of the forces of this new field. Studying the electrostatic field, we found out that the work of the forces of the electrostatic field in a closed loop is equal to zero. Since when the charge moves in one direction, the displacement and the acting force are co-directed and the work is positive, then when the charge moves in the opposite direction, the displacement and the acting force are oppositely directed and the work is negative, the total work will be equal to zero. In the case of a vortex field, the closed loop operation will be nonzero. So when the charge moves along a closed line of an electric field, which has a vortex character, work in different sections will maintain a constant sign, since the force and movement in different sections of the trajectory will maintain the same direction relative to each other. The work of the forces of the vortex electric field on the movement of the charge along the closed circuit is nonzero, therefore, the vortex electric field can generate an electric current in the closed circuit, which coincides with the experimental results. Then it can be argued that the force acting on the charges from the vortex field is equal to the product of the transferred charge and the strength of this field.
This force is the outside force that does the work. The work of this force, referred to the value of the transferred charge, is the EMF of induction. The direction of the vortex electric field strength vector at each point of the strength lines is determined by the Lenz rule and coincides with the direction of the induction current.
An induction electric current arises in a stationary circuit in an alternating magnetic field. The magnetic field itself cannot be a source of external forces, since it can only act on orderly moving electric charges. There can be no electrostatic field, since it is generated by stationary charges. After the assumption that a time-varying magnetic field generates an electric field, we learned that this alternating field is of a vortex nature, that is, its lines are closed. The work of the vortex electric field in a closed loop is nonzero. The force acting on the transferred charge from the side of the vortex electric field is equal to the value of this transferred charge multiplied by the intensity of the vortex electric field. This force is the third-party force that leads to the emergence of EMF in the circuit. The electromotive force of induction, that is, the ratio of the work of external forces to the value of the transferred charge, is equal to the rate of change of the magnetic flux taken with a minus sign. The direction of the intensity vector of the vortex electric field at each point of the lines of intensity is determined by the Lenz rule.
- Kasyanov V.A., Physics 11th grade: Textbook. for general education. institutions. - 4th ed., Stereotype. - M .: Bustard, 2004 .-- 416 p.: Ill., 8 p. color incl.
- Gendenshtein L.E., Dick Yu.I., Physics 11. - M .: Mnemosyne.
- Tikhomirova S.A., Yarovsky B.M., Physics 11. - M .: Mnemosina.
- Electronic textbook of physics ().
- Cool physics ().
- Xvatit.com ().
- How can you explain the fact that a lightning strike can melt fuses, damage sensitive electrical appliances and semiconductor devices?
- * When the ring was opened, an EMF of self-induction of 300 V arose in the coil. What is the intensity of the vortex electric field in the turns of the coil, if their number is 800, and the radius of the turns is 4 cm?
Alternating magnetic field generates induced electric field... If the magnetic field is constant, then the induced electric field will not arise. Consequently, the induced electric field is not related to chargesas in the case of an electrostatic field; its lines of force do not begin or end at charges, but are closed on themselveslike the lines of force of a magnetic field. It means that induced electric fieldlike magnetic is vortex.
If a stationary conductor is placed in an alternating magnetic field, then e is induced in it. etc. with. Electrons are set in directional motion by an electric field induced by an alternating magnetic field; an induced electric current occurs. In this case, the conductor is only an indicator of the induced electric field. The field sets in motion free electrons in the conductor and thereby reveals itself. Now it can be argued that this field exists even without a conductor, having a reserve of energy.
The essence of the phenomenon of electromagnetic induction lies not so much in the appearance of an induced current as in the appearance of a vortex electric field.
This fundamental position of electrodynamics was established by Maxwell as a generalization of Faraday's law of electromagnetic induction.
In contrast to the electrostatic field, the induced electric field is non-potential, since the work performed in the induced electric field, when a single positive charge moves along a closed loop, is equal to e. etc. with. induction, not zero.
The direction of the vector of intensity of the vortex electric field is established in accordance with the Faraday law of electromagnetic induction and Lenz's rule. The direction of the lines of force of the vortex el. field coincides with the direction of the induction current.
Since the vortex electric field exists in the absence of a conductor, it can be used to accelerate charged particles to speeds comparable to the speed of light. It is on the use of this principle that the action of electron accelerators - betatrons is based.
An induction electric field has completely different properties than an electrostatic field.
The difference between a vortex electric field and an electrostatic
1) It is not associated with electrical charges;
2) The lines of force of this field are always closed;
3) The work of the forces of the vortex field on the movement of charges on a closed trajectory is not equal to zero.
|
electrostatic field |
induction electric field |
| 1. created by motionless electr. charges | 1.Caused by changes in the magnetic field |
| 2.the field lines are open - potential field | 2.the lines of force are closed - vortex field |
| 3. field sources are electr. charges | 3.field sources cannot be specified |
| 4. the work of the field forces to move the test charge along a closed path \u003d 0. | 4.the work of the field forces to move the test charge along a closed path \u003d EMF of induction |
