Charged bodies can be obtained by electrifying.
Electrification of the body- This mechanical process as a result of which a body has a shortage or excess of electrons.
Electrification can occur in several ways:
CONTACT
(bring a charged body to a metal sleeve, it will first be attracted, and then repelled).
IMPACT
(rubber hose hit sharply on a massive object and bring it to the electroscope).
FRICTION
(rubbing a glass rod on silk will give a positive charge).
Properties electric field:
The electric field acts on the charge Fel introduced into this field
The field is stronger near charged bodies, and weaker as it moves away
The electric field can be detected using a test charge (by the effect on the test charge)
Main characteristics of the electric field
| Characteristics of the electric field | Formula | Peculiarities |
| Electric charge- electric field source | 1) The law of conservation of electric charge: In a closed system, the algebraic sum of the charges of all particles remains unchanged.
2) If two charges are connected, then separated, then the resulting charges will be equal  3) Electrostatic (or Coulomb) repulsion occurs between like-charged bodies, and electrostatic attraction between oppositely charged bodies. Example: Two small identical balls have charges of 4 Kli -9 Kl. What will be the charge of each ball if they are brought into contact and then moved apart again? | |
| Electric force Coulomb's law - force of interaction of 2 point charged bodies is directly proportional to the product of the modules of the charges and inversely proportional to the square of the distance between them. |
if charges in vacuum or in air
if the charge in a medium with a dielectric  Example: The modulus of the force of action of one motionless point charged body on another is equal to F. What will be the modulus of this force if we increase the charge of one body by 2 times, and the second - by 3 times? | - relative permittivity of the medium - a number showing how many times the tension electrostatic field in a homogeneous dielectric is less than the tension in vacuum. k=9 10 9 |
| Electric field strength - power characteristic of the electric field. The direction of the tension vector coincides with the direction of the force acting on the positive charge. | Tension is a vector quantity equal at each point to the ratio of the force acting on a trial charge placed at this point of the field to the magnitude of this charge: Electric field strength for point charge | The lines of force of the electric field are lines, the tangents to which at each point of the field coincide with the direction of the intensity vector. The density of the lines is chosen so that the number of lines penetrating a unit surface perpendicular to the lines of the site would be equal to the modulus of the intensity vector. |
| The principle of tension superposition - if at some point in space different charges create electric fields, then the resulting tension at this point will be equal to the vector sum of the intensities of each field. |  Example1.: Find the tension at the midpoint if q 1 \u003d 8nCl, q 2 \u003d -6nCl E \u003d E 1 + E 2  Example2.: Find the tension at a point remote from the first charge at a distance of 8cm, and from the second at 6cm, if q 1 \u003d 8nC, q 2 \u003d -6nC  Example3.: Find the tension at a point remote from the first charge at a distance r 1, and from the second at r 2, if q 1 \u003d 8nC, q 2 \u003d -6nC  | Tension lines of charged bodies:  |
| Potential - energy characteristic of the field. The ratio of potential energy to charge. Surfaces of equal potential are called equipotential. Potential difference = Voltage The principle of superposition of field potentials: if the field is created by several charges, the potential at any point is equal to the algebraic sum of the potentials created at this point by each charge separately. |  Point charge potential
Relationship between potential and tension 
| The potential of the field of a positive charge decreases with distance from the charge, and the potential of the field of a negative charge increases. In conductors, positive charges move away from the potential  negative charges - vice versa Lines of tension are directed in the direction of decreasing potential |
| The work of the force of the electrostatic field |  Example: What work will the field do to transfer charge q 1 from point A to B 
 
| 
|
| Work on the transfer of charge q 1 from a point with potential to the point of potential | 
| |
| Electric field energy (charged conductor) |  
|
Part 2
Electric capacity C is a feature electrical properties conductor, which determines the possibility of accumulating charges on this conductor.
Electrical capacity is the ratio of the conductor's charge to its potential.
A capacitor consists of two conductors charged with opposite charges equal in absolute value. The conductors that form the capacitor are called its plates. The simplest capacitor is a system of two flat conductive plates arranged parallel to each other at a small distance compared to the dimensions of the plates and separated by a dielectric layer. Such a capacitor is called flat. The electric field of a flat capacitor is mainly localized between the plates
The electrical capacity does not depend on:
In the SI system, the unit of electrical capacity is called farad(F):
When solving problems of electrostatics and answering certain qualitative questions, it is useful to keep in mind the following:
1. Positive electric charges, left to themselves, move in an electric field from points with a large potential to points where the potential is less. Negative charges move in the opposite direction.
2. The electric field strength inside a statically charged conductor is zero. This result does not depend on whether an external electric field or not. The potential of all points lying on the conductor has in this case same value, i.e. the surface of the conductor is equipotential.
3. The potential of the earth and all bodies connected by a conductor to the earth is assumed to be zero.
4. The work of the forces of the electrostatic field in any closed circuit is zero.
5. If two solitary balls are connected with a thin and long wire, then their total capacity will be equal to the sum of the capacities of the individual balls, since the potentials of the balls will be the same, and the total charge of the system is equal to the sum of the charges of the balls.
For the same reason, a solitary ball can be considered as two capacitors connected in parallel with each other, with equal capacities.
6. The electric field of a charged capacitor can be considered as the result of the superposition of two fields created by each capacitor plate. If the fields created by the plates of a flat charged capacitor can be considered uniform, then the field strength in the capacitor will be 2 times greater than the field strength created by one infinite charged plane.
7. If you connect a flat capacitor to a power source, charge it and then turn it off, then when the capacitance C of the capacitor changes due to the expansion (convergence) or displacement of the plates, the introduction (removal) of a dielectric, the charge on the capacitor does not change.
8. If a battery of capacitors is connected to a voltage source and given some charge, then the algebraic sum of the charges of any group of plates isolated from the source must always be zero, since the charges in this group of plates are separated due to induction.
There are many phenomena in nature that man still does not fully understand. These include electric fields, the characteristics of which we already know how to determine fairly well. At the same time, it is not always possible to use them. This direction is more theoretical and, most likely, will not provide benefits in the short term of study, and now more emphasis is placed on such developments. Thus, the possibilities of such fields are mainly explored by enthusiasts, and it is definitely not worth expecting radical breakthroughs in the near future.
As in many other cases, it is necessary to begin the description of this phenomenon with its definition. From the point of view of modern science, it is special variant matter created by charged bodies. It is possible to detect the electric field and its characteristics due to the interaction of charges with each other. They are the main constituent elements of this phenomenon. It is impossible to detect it with ordinary vision, but a person has many other senses. And with their help, it is quite possible to determine the presence of such a field. The simplest example is to bring your hand up to the TV screen. He, like any other electronic devices, creates around himself just such a field, to which the hairs on the arm react. As a result, a person gets the opportunity, very conditionally, but still to determine the presence or absence of such a phenomenon.
These concepts should not be confused. The main characteristics of the electric field indicate that it is part of its electromagnetic counterpart. In fact, there are two elements in the composition of this phenomenon, one of which is discussed in this article, and the second logically follows from the name. This is a magnetic field. They always interact with each other and are usually considered together, but have different features, and therefore in some cases it is better to separate them.
Each such phenomenon has certain features that constantly remain unchanged. So, whatever the energy characteristic of the electric field, the following properties can be distinguished:
Modern science already knows how to consciously create such phenomena and even control them within certain limits, but it is still very far from fully putting them at the service of man.
This is one of the characteristics of the electric field. Tension is used when it is required to determine the "quantity" of such a phenomenon in a certain place. It is quite difficult to imagine this, especially without sufficient knowledge of physics, since this indicator refers specifically to this direction Sciences. So, this value is calculated as the ratio of the test positive charge to the force of action. And at the same time, the characteristic refers to vector indicators. That is, its direction is necessarily similar to that which affects the test charge. Simply put, tension is the strength or power of an electric field at a specific time in a specific place. The higher this indicator, the stronger this phenomenon affects the surrounding objects or living beings.
This is another characteristic of the electric field. Potential is the stored energy that a phenomenon can use to move charges. When it starts to move, this same resource is spent on it, and eventually it becomes equal to zero. It accumulates in the opposite way. As an example, we can take the same charge, but located outside the electric field. As soon as some force moves it inward and moves it there, there is a potential.
The easiest way to imagine this is on the example of a conventional spring. In its resting position, it has no potential and is simply a bent piece of metal. But as soon as we start squeezing it, the potential will begin to arise. If you release the spring, it instantly straightens and at the same time moves all the objects that it can, located in its path. If we return to the considered electric fields, then in their case the potential will strictly correspond to the applied efforts to move the charge. In modern science, this indicator is measured in volts.
In fact, any such phenomenon can be described by the two previous indicators. But voltage is also a characteristic of the electric field. It is derived from the potential and shows what kind of work, in quantitative terms, the phenomenon has produced. On the example of the same spring, the voltage will be the indicator to which it unfolded after compression. That is, if the potential is the total "accumulated energy", then this parameter already makes it clear how much of it was spent on the movement of charges.
The characteristics of electric fields imply the presence of two main properties that are used by humans. So, they can form ions, and electrodes immersed in liquid make it possible to separate it, roughly speaking, into fractions without much effort. These properties are based on the use of electric fields.
There are many other use cases as well. For example, an electromagnetic field, which also includes the phenomenon considered in this article, can serve as a wireless system for transmitting electricity to various devices. Unfortunately, in most cases, all such developments are rather theoretical and experimental.
We are surrounded by an electric field all the time. Its properties and characteristics are usually of the same type and constant, so that the natural background characteristic of our planet has practically no effect on a person. This effect becomes a little brighter during a serious thunderstorm, when it seems that the air is literally trembling with tension. But even this does not pose any threat to the vast majority of people.
Nevertheless, progress does not stand still, and constantly appears a large number of devices, each of which generates its own electric field. Moreover, it is much stronger than the natural background, which is 0.5 kV / m. Of course, this feature has not gone unnoticed. The maximum allowable voltage has long been deduced, in which we can exist almost indefinitely. It is 25 kV/m. Under normal conditions, even with the activation of all household appliances, this indicator is not exceeded. The average person can get a large "dose" only when they are (and for a long time) in close proximity to high-voltage wires. There, the voltage is already much higher and it is highly not recommended to stand nearby (and even more so work) for a long time. Even those specialists who, on duty, are forced to be near sources of such electric fields should not do this for more than an hour and a half a day. So, if there are any territories that are adjacent to power lines, the time of presence there should be limited as much as possible.
Within the framework of this article, we have considered all the basic features, properties and characteristics of electric fields. Based on the foregoing, we can conclude that it is a very interesting phenomenon, the full study of which can greatly help humanity in the distant future.
>>Physics: Electric field
After a long struggle, the theory of short-range action won a final victory. We will briefly describe how this happened, as well as what an electric field is.
Faraday's ideas. A decisive turn towards the concept of short-range action was made by the great English scientist Michael Faraday, and finally completed by the English scientist James Maxwell.
According to the theory of action at a distance, one charge directly senses the presence of another. When moving one of the charges, for example A (fig.14.6), the force acting on another charge - B, instantly changes its value. And not with the charge itself B, no changes occur to the surrounding space.
According to Faraday's idea, electric charges do not act directly on each other. Each of them creates in the surrounding space electric field. The field of one charge acts on another charge, and vice versa. As you move away from the charge, the field weakens. Initially, this idea expressed only Faraday's confidence that the action of one body on another through a void is impossible.
There was no evidence for the existence of the field. Such evidence cannot be obtained by examining only the interaction stationary charges. Success came to the theory of short-range interaction after studying the electromagnetic interactions of moving charged particles. First, the existence of time-varying fields was proved, and only after that was it concluded that the electric field of stationary charges was real.
Velocity of propagation of electromagnetic interactions. Based on the ideas of Faraday, Maxwell was able to theoretically prove that electromagnetic interactions must propagate in space at a finite speed.
This means that if we slightly move the charge A(see Fig. 14.6), then the force acting on the charge IN, will change, but not at the same instant, but only after some time:
Where AB is the distance between the charges, and With- speed of propagation of electromagnetic interactions. Maxwell showed that the speed c is equal to the speed of light in vacuum, i.e. approximately 300,000 km/s. When moving charge A electric field around the charge IN will change over time t. This means that some process occurs between the charges in vacuum, as a result of which the interaction between them propagates at a finite speed.
The existence of a certain process in space between interacting bodies, which lasts a finite time, is the main thing that distinguishes the theory of short-range action from the theory of action at a distance. All other arguments in favor of one theory or another cannot be considered decisive. True, the experiment to verify equality (14.6) when moving charges is difficult to implement due to of great importance speed With. But now, after the invention of the radio, there is no need for this.
Radio waves. The transmission of information using electromagnetic waves is called radio communication. Now you can read in the newspapers that radio waves from a space station approaching Venus reach the Earth in more than 4 minutes. The station may already burn out in the atmosphere of the planet, and the radio waves sent by it will wander in space for a long time. Thus, the electro-magnetic field reveals itself as something really existing.
What is an electric field? We know that the electric field really exists: its properties can be investigated empirically. But we cannot say what this field consists of. Here we reach the limit of what science knows.
The house consists of bricks, slabs and other materials, which, in turn, consist of molecules, molecules - from atoms, atoms - from elementary particles. More simple formations than elementary particles, we do not know. The same is the case with the electric field: we do not know anything simpler than a field. Therefore, we can only say the following about the nature of the electric field:
Firstly, the field is material; it exists independently of us, from our knowledge of it;
secondly, the field has certain properties that do not allow it to be confused with anything else in the surrounding world.
The establishment of these properties forms our ideas about what an electric field is.
When studying the electric field, we are faced with special kind matter, the movement of which does not obey the laws of Newtonian mechanics. With the discovery of the electric field, for the first time in the history of science, a profound idea emerged: there are different kinds matter and each of them has its own properties.
Basic properties of the electric field. The main property of an electric field is its action on electric charges with some force. Based on the action on the charge, the existence of the field is established, its distribution in space, and all its characteristics are studied.
The electric field of stationary charges is called electrostatic. It doesn't change with time. An electrostatic field is generated only electric charges. It exists in the space surrounding these charges and is inextricably linked with them.
As we study electrodynamics, we will get acquainted with new properties of the electric field. Let's get acquainted with the time-varying electric field, which is no longer inextricably linked with charges.
Many properties of static and variable fields are the same. However, there are also significant differences between them. Speaking about the properties of the field, we will call this field simply electric if this property is equally inherent in both static and variable fields.
According to the theory of short-range interaction, the interaction between charged particles is carried out by means of an electric field. - This special shape matter that exists independently of our ideas about it. Evidence of the reality of the electric field - the final speed of propagation of electromagnetic interactions and the action of the field on charged bodies.
???
1. What is the difference between the theory of short-range action and the theory of action at a distance?
2. What are the main properties of an electrostatic field?
G.Ya.Myakishev, B.B.Bukhovtsev, N.N.Sotsky, Physics Grade 10
Lesson content lesson summary support frame lesson presentation accelerative methods interactive technologies Practice tasks and exercises self-examination workshops, trainings, cases, quests homework discussion questions rhetorical questions from students Illustrations audio, video clips and multimedia photographs, pictures graphics, tables, schemes humor, anecdotes, jokes, comics parables, sayings, crossword puzzles, quotes Add-ons abstracts articles chips for inquisitive cheat sheets textbooks basic and additional glossary of terms other Improving textbooks and lessonscorrecting errors in the textbook updating a fragment in the textbook elements of innovation in the lesson replacing obsolete knowledge with new ones Only for teachers perfect lessons calendar plan for a year guidelines discussion programs Integrated LessonsIf you have corrections or suggestions for this lesson,
