An electric field is a material object that makes interaction between charged bodies possible. Field strength: essence and main characteristics How to prove that the electric field is material

We always receive signals about distant events using an intermediate medium. For example, telephone communication is carried out using electrical wires, speech transmission over a distance occurs using sound waves spreading in the air

(sound cannot travel in airless space). Since the occurrence of a signal is always a material phenomenon, its propagation, associated with the transfer of energy from point to point in space, can only occur in a material environment.

The most important sign that an intermediate medium is involved in signal transmission is the final speed of signal propagation from the source to the observer, which depends on the properties of the medium. For example, sound in air travels at a speed of about 330 m/s.

If there were phenomena in nature in which the speed of propagation of signals was infinitely large, i.e., a signal would be instantly transmitted from one body to another at any distance between them, then this would mean that bodies could act on each other at a distance and in the absence of matter between them. In physics, this effect of bodies on each other is called long-range action. When bodies act on each other with the help of matter located between them, their interaction is called short-range action. Consequently, during close interaction, the body directly affects the material environment, and this environment already affects another body.

It takes some time to transfer the influence of one body to another through an intermediate medium, since any processes in the material environment are transmitted from point to point with a finite and well-defined speed. The mathematical justification for the theory of short-range action was given by the outstanding English scientist D. Maxwell (1831-1879). Since signals that propagate instantly do not exist in nature, in what follows we will adhere to the short-range theory.

In some cases, the propagation of signals occurs through matter, for example, the propagation of sound in air. In other cases, the substance is not directly involved in the transmission of signals, for example, light from the Sun reaches the Earth through airless space. Therefore, matter exists not only in the form of substance.

In cases where the impact of bodies on each other can occur through airless space, the material medium transmitting this impact is called a field. Thus, matter exists in the form of substance and in the form of? fields. Depending on the type of forces acting between bodies, fields can be various types. A field that transmits the influence of one body on another in accordance with the law universal gravity, is called the gravitational field. The field that transmits the effect of one stationary electric charge on another stationary charge in accordance with Coulomb's law is called an electrostatic or electric field.

Experience has shown that electrical signals propagate in airless space at a very high but finite speed, which is approximately 300,000 km/s (§ 27.7). This

proves that the electric field is the same physical reality as matter. The study of the properties of the field made it possible to transfer energy over a distance using the field and use it for the needs of humanity. An example is the effect of radio communications, television, lasers, etc. However, many properties of the field have been poorly studied or are not yet known. Studying physical properties fields and the interaction between field and matter is one of the most important scientific problems modern physics.

Any electric charge creates an electric field in space, with the help of which it interacts with other charges. The electric field only acts on electric charges. Therefore, such a field can be detected in only one way: by introducing a test charge into a point in space that interests us. If there is a field at this point, then it will act electric force.

When the field is examined with a test charge, it is believed that its presence does not distort the field under study. This means that the magnitude of the test charge must be very small compared to the charges creating the field. It was agreed to use a positive charge as a test charge.

From Coulomb's law it follows that absolute value The force of interaction between electric charges decreases with increasing distance between them, but never disappears completely. This means that, theoretically, the electric charge field extends to infinity. However, in practice we believe that the field is present only where a noticeable force acts on the test charge.

Let us also note that when a charge moves, its field also moves with it. When the charge is removed so much that the electric force on the test charge at any point in space has practically no effect, we say that the field has disappeared, although in reality it has moved to other points in space.

The electric field, according to elementary physical concepts, is nothing more than special kind material environment, arising around charged bodies and influencing the organization of interaction between such bodies with a certain finite speed and in a strictly limited space.

It has long been proven that an electric field can arise in both stationary and moving bodies. The main indication of its presence is its effect on

One of the main quantitative ones is the concept of “field strength”. In numerical terms, this term means the ratio of the force that acts on a test charge directly to the quantitative expression of this charge.

The fact that the charge is trial means that he himself had no participation in the creation of this field does not accept, and its value is so small that it does not lead to any distortion of the original data. The field strength is measured in V/m, which is conventionally equal to N/C.

The famous English researcher M. Faraday introduced the method into scientific circulation graphic image electric field. In his opinion, this special type of matter should be depicted in the drawing as continuous lines. They subsequently became known as “electric field strength lines,” and their direction, based on the basic physical laws, coincides with the direction of tension.

Lines of force are needed to show such quality characteristics tension, such as density or density. In this case, the density of tension lines depends on their number per unit surface. The created picture of the field lines allows you to determine the quantitative expression of the field strength in its individual sections, as well as find out how it changes.

The electric field of dielectrics has quite interesting properties. As is known, dielectrics are substances in which there are practically no free charged particles, therefore, as a result, they are not capable of conducting. Such substances should include, first of all, all gases, ceramics, porcelain, distilled water, mica, etc.

In order to determine the field strength in a dielectric, an electric field must be passed through it. Under its influence, the bound charges in the dielectric begin to shift, but they are not able to leave the confines of their molecules. The directional displacement implies that positively charged ones are displaced along the direction of the electric field, and negatively charged ones - against. As a result of these manipulations, a new electric field appears inside the dielectric, the direction of which is directly opposite to the external one. This internal field noticeably weakens the external one, therefore, the tension of the latter drops.

Field strength is its most important quantitative characteristic, which is directly proportional to the force with which this special type of matter acts on an external electric charge. Despite the fact that it is impossible to see this value, with the help of a drawing of field lines of tension you can get an idea of ​​​​its density and direction in space.

TYPE OF LESSON: Lesson on learning new material.

LESSON OBJECTIVES:

Educational:

1. Form one of the basic concepts of electrodynamics - electric field.
2. Form an idea of ​​matter in two forms: substance and field.
3. Show methods for detecting an electric field.

Educational:

1. Develop students’ abilities to analyze, compare, identify significant features, and draw conclusions.
2. Develop abstract and logical thinking of students.

Educators:

1. Using the example of the struggle between the theories of short-range and long-range action, show the complexity of the cognition process.
2. Continue to form a worldview using the example of knowledge about the structure of matter.
3. Develop the ability to prove and defend your point of view.

EQUIPMENT:

• graphic projector;
• a device for demonstrating electric field spectra;
• high-voltage converter “Discharge”;
• current source;
• connecting wires;
• electrometer;
• fur, plexiglass stick;
• paper figures;
• a piece of cotton wool, wire;
• transformer;
• a turn of wire with a 3.5V lamp.

Didactic moment: taking into account knowledge, abilities, skills.

Reception: frontal survey.

Teacher: Remember what an electric charge is.
Student: Electric charge is the property of bodies to carry out electromagnetic interaction with each other with forces that decrease with increasing distance in the same way as the forces of universal gravity, but exceed the gravitational forces several times.
Teacher: Is it possible to say: “A free charge has flown.”
Student: No. An electric charge is always present on a particle; there are no free electric charges.
Teacher: What types of electric charges do you know and how do they interact?
Student: In nature there are particles with positive and negative charges. Two positively charged or two negatively charged particles repel, while positively and negatively charged particles attract.
Teacher: Indeed, the charges are just like in human life. Two energetic, active people cannot be together for a long time, the same is repelled. Energetic and calm get along well, different things attract.
Teacher: In electrostatics, we know Coulomb's law for the interaction of charges. Write down and formulate this law.
Student: F = k|q1| |q2| / rІ (writes on the board, pronounces the law out loud).

The force of interaction between two point stationary charged bodies in a vacuum is directly proportional to the product of the charge modules and inversely proportional to the square of the distances between them. If at least one charge is increased, the interaction force will increase; if the distance between the charges is increased, the force will decrease.

Didactic moment: propaedeutics of learning new material.
Reception: problematic situation.

Teacher: Okay, we remembered the main things we covered. Have you ever wondered how one charge acts on another?

Experience: I place cotton wool on the negative pole of the high-voltage converter. It acquires a minus sign. An electric force acts on the fleece from the positive pole. Under its influence, vata jumps to the positive pole, acquires a “plus” sign, etc.

Teacher: How does one charge act on another? How are electrical interactions carried out? Coulomb's law does not answer this. Problem ...Let's take a break from electrical interactions. How do you interact with each other, how, for example, will Anya attract Katya’s attention?
Student: I can take her hand, push her, throw a note, ask someone to call her, shout, whistle.
Teacher: All your actions from the point of view of physics have something in common: who noticed this commonality?
Student: Interaction is carried out through intermediate links (hands, shoulders, notes), or through the medium (sound propagates in the air).
Teacher: What is the conclusion?
Student: For the interaction of bodies, a certain physical process in the space between interacting bodies.
Teacher: So, we figured out the interaction between people. How do electric charges interact? What are the intermediate links, the medium that carries out electrical interactions?

Didactic moment: learning new material.
Techniques: explanation based on students' knowledge, elements of argument, elements of game, presentation of theory in verse, demonstration experiment.
Teacher: There was a long dispute in physics about this between supporters of the theories of short-range and long-range action. Now we will become supporters of these theories and try to argue..
(I divide the class and the board into two halves. On the right side of the board I write: “Theory of short-range action.” A crossword puzzle is also drawn here, Figure 1).

(On the left side of the board I write: “Theory of long-range action.” A crossword puzzle is drawn here, Figure 2).

Teacher: So, the right side of the class are supporters of the theory of short-range action. Agreed?
The left side is the supporters of the theory of long-range action. Agreed?
(I move to the right side of the class).

Teacher: Well, let's start arguing. I am presenting the essence of the theory of short-range action, and you help me, guess the words written on the board.

We are proponents of close action

Between the bodies there must be Wednesday.
Links for communication, not emptiness.
Processes in that environment move quickly,
But not instantly. Their speed finite.
(Then I repeat again, without pause, I ask all supporters of the theory of short-range action to pronounce the highlighted words).

Teacher: Give examples that prove your theory.
Student: 1. Sound travels through air or other medium at a speed of 330 m/s.

2. Press the brake pedal, the brake fluid pressure at the final speed is transmitted to the brake pads.
(I move to the left side of the class)

Teacher: Proponents of the theory of long-range action. I am presenting the essence of the theory of long-range action, and you help me, guess the words written on the board.

We are long-range advocates
We affirm: for interaction
One is needed emptiness,
And not some links, Wednesday.
The interaction of bodies is certain
It happens in that emptiness instantly.

(Then I repeat again, without pause, I ask all supporters of the theory of long-range action to pronounce the highlighted words)

Teacher: Give examples that prove your theory?
Student: 1. I press the switch, the light turns on instantly. 2. I electrify the rod against the bellows, bring it to the electrometer, the electrometer needle instantly deflects (shows experience with an electrometer).
Teacher: Let's make notes in the notebook:

Short Range Theory:

1. Electrical interaction is carried out through a medium, intermediate links.
2. Electrical interaction is transmitted at a finite speed.

Long Range Theory:

1. Electrical interaction occurs through the void.
2. Electrical interaction is transmitted instantly.

Teacher: What should I do? Who is right? To resolve the dispute we need...?

Class: Idea.

Teacher: Yes, an idea is a rare game in the forest of words. /V.Hugo/

The dispute was completed by the idea generator -
English scientist Michael Faraday.

What is Faraday's idea? Open page 102 paragraph 38, point 1.

I'll give you 3 minutes to catch Faraday's brilliant idea. ( The class reads, the teacher changes the position of the devices).

Student: According to Faraday's idea, electric charges do not act on each other directly. 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.

Teacher: So who is right: supporters of the theories of long-range action or short-range action?

Student: Proponents of the theory of short-range action.

Teacher: What is the intermediate link that carries out electrical interaction?

Student: Electric field.

Teacher: So why does a charged cotton wool interact with a charged ball at a distance, remember the experiment?

Student: The electric field of a charged ball acts on the cotton wool.

Teacher: Electric field... It’s easy to say, but difficult to imagine. Our senses are not able to see or record this field. So what is an electric field? (Formulation of points 1) – 4) we create together, students make notes in a notebook).

Electric field: ( writing in a notebook). Verbal comments from the teacher or students.

1). A type of matter that exists in space near charged bodies.	1) Matter can exist in two forms: substance and field. We perceive the substance directly with our senses, the field indirectly, through something.
2). The field is material and exists independently of us.	2) (a) Radio waves are electromagnetic fields. They propagate in space even when their source (for example, a radio station) is not working.
(b) A microwave oven heats food using the energy of an electric field. This means that the electric field exists. It is material, because has energy.	3). The electric field propagates with a final speed c = 3* 10 8 m/s.
4). The main property of the electric field is its effect on electric charges with some force.	4) Experience: the electric field of the plexiglass plate acts on the paper figures with force, causing them to move and “dance”.

Teacher: Would you like to “see” the electric field?

This is impossible with our senses. Small particles (semolina) poured into machine oil and placed in a strong electric field will help us.

Experience. (The device is used to demonstrate the spectra of electric fields).

I take a cuvette with oil and semolina, stir it on a graphic projector, and apply voltage from the “Discharge” to the electrodes. Opposite charges appeared on the electrodes. What do we see, how can we explain it?

Student: There is an electric field around the electrodes; grains of semolina became electrified and, under the influence of the field, began to be located along certain lines, because the field acts on the grains with force.

Teacher: The grains line up power lines electric field, reflecting his “picture”. Where the lines are denser, the field is stronger, and where the lines are denser, the field is weaker. The lines stretch towards each other, which means the fields have different names.

The field of the two plates is different. The field lines are parallel. Such a field is the same at all points and is called homogeneous.

I will place a metal ring in the field of two plates,” inside the ring the grains do not rearrange. What does this mean?

Student: There is no electric field inside the metal ring.

Didactic point: generalization; brief account of knowledge.
Techniques: express survey using signal cards; guesswork experience.

Teacher: So what did we learn today, what remains in our heads? Let's check. On your tables there are 5 cards of different colors. I ask a question, you pick up the card on which, from your point of view, the correct answer: the colored side is towards me, the text is towards you. By color I can quickly figure out who has learned what. (The teacher records the result of the express survey).

Express survey.

Question 1. The essence of the theory is close to action? (Red card).

Question 2. The essence of the theory of long-range action? (Blue card).
Question 3. The essence of Faraday's idea? (Green card).
Question 4. What is an electric field? (White card).

(The fifth card (orange) does not correspond to any of the questions.)

Card texts.

1. Red card: bodies interact through intermediate links with the final one
   speed.
2. Blue card: bodies interact through the void instantly.
3. Green card: electrical interaction occurs due to
   electric field.
4. White card: a type of matter that exists in space near charged bodies. The field, independent of us, propagates at a finite speed and acts with some force on the charge.

Result: the teacher says how many people in the class answered the questions correctly and names the correct colors of the cards. Well done!

Teacher: And now – the experiment is on its way.

Experience: I connect a transformer to the network. Charges move in its windings, around which, as you know, an electric field is created. I take a turn of wire and a lamp. The coil is not connected to the network. I bring it to the transformer. Why does the lamp glow, because it is not connected to the electrical network?

Student: There is an electric field around the windings of the transformer, which acts on the charges in the coil with a force, sets the charges in motion, current flows through the lamp, and the lamp glows. The field is material. The electric field exists!

Didactic point: homework.
Reception: writing paragraphs in a diary from the board.

§37, questions p. 102, §38, questions p. 104. (Myakishev G.Ya., Bukhovtsev B.B. Textbook for 10th grade educational institutions. - 8th ed. - M.: Prosv., 2000 ).

VI STAGE

Didactic moment: summing up.

Technique: taking into account the correct answers of students during the lesson with subsequent generalization; grading.