The topic of today's lesson is devoted to an important topic - "Magnetic flux". To begin with, we recall what electromagnetic induction is. After that, we will talk about what causes the induction current and what is the main thing for this current to appear. From Faraday's experiments, we learn how a magnetic flux arises.

Continuing the study of the topic "Electromagnetic induction", let's take a closer look at such a concept as magnetic flux.

You already know how to detect the phenomenon of electromagnetic induction - if a closed conductor is crossed by magnetic lines, an electric current arises in this conductor. Such a current is called inductive.

Now let's discuss how this electric current is generated and what is the main thing for this current to appear.

First of all, let's turn to Faraday's experience and look again at its important features.

So, we have an ammeter available, a coil with a large number of turns, which is short-circuited to this ammeter.

We take a magnet, and in the same way as in the previous lesson, we lower this magnet into the coil. The arrow deviates, that is, there is an electric current in this circuit.

Rice. 1. Experience in detecting induction current

But when the magnet is inside the coil, there is no electric current in the circuit. But as soon as you try to get this magnet out of the coil, an electric current reappears in the circuit, but the direction of this current changes to the opposite.

Please also note that the value of the electric current that flows in the circuit also depends on the properties of the magnet itself. If you take another magnet and do the same experiment, the value of the current changes significantly, in this case the current becomes smaller.

After conducting experiments, we can conclude that the electric current that occurs in a closed conductor (in a coil) is associated with the magnetic field of a permanent magnet.

In other words, the electric current depends on some characteristic of the magnetic field. And we have already introduced such a characteristic -.

Recall that magnetic induction is denoted by the letter, it is a vector quantity. And the magnetic induction is measured in Tesla.

Tesla - in honor of the European and American scientist Nikola Tesla.

Magnetic induction characterizes the effect of a magnetic field on a current-carrying conductor placed in this field.

But, when we talk about electric current, we must understand that electric current, and you know this from grade 8, arises under the influence of an electric field.

Therefore, we can conclude that the electric induction current appears due to the electric field, which in turn is formed as a result of the magnetic field. And such a relationship is just carried out due to magnetic flux.

What is magnetic flux?

magnetic flux denoted by the letter Ф and expressed in units such as weber, and denoted by .

Magnetic flux can be compared to the flow of a liquid flowing through a limited surface. If you take a pipe, and liquid flows in this pipe, then, accordingly, a certain flow of water will flow through the cross-sectional area of ​​\u200b\u200bthe pipe.

The magnetic flux, by this analogy, characterizes how many magnetic lines will pass through a limited circuit. This contour is the area bounded by a wire coil or, perhaps, by some other form, while this area is necessarily limited.

Rice. 2. In the first case, the magnetic flux is maximum. In the second case, it is equal to zero.

The figure shows two turns. One turn is a wire turn through which the lines of magnetic induction pass. As you can see, there are four of these lines. If there were much more of them, then we would say that the magnetic flux would be large. If there were fewer of these lines, for example, we would draw one line, then we could say that the magnetic flux is small enough, it is small.

And one more case: when the coil is located in such a way that magnetic lines do not pass through its area. It seems that the lines of magnetic induction slide over the surface. In this case, we can say that there is no magnetic flux, i.e. there are no lines that would penetrate the surface of this contour.

magnetic flux characterizes the entire magnet as a whole (or another source of magnetic field). If magnetic induction characterizes the action at any one point, then the magnetic flux is the entire magnet. We can say that the magnetic flux is the second very important characteristic of the magnetic field. If magnetic induction is called the power characteristic of the magnetic field, then the magnetic flux is the energy characteristic of the magnetic field.

Returning to the experiments, we can say that each turn of the coil can be represented as a separate closed turn. The same circuit through which the magnetic flux of the magnetic induction vector will pass. In this case, an inductive electric current will be observed.

Thus, it is under the influence of the magnetic flux that an electric field is created in a closed conductor. And already this electric field creates nothing more than an electric current.

Let's look again at the experiment, and now, already knowing that there is a magnetic flux, let's look at the relationship between the magnetic flux and the value of the inductive electric current.

Let's take a magnet and pass it slowly enough through the coil. The value of the electric current changes very little.

If you try to pull out the magnet quickly, then the value of the electric current will be greater than in the first case.

In this case, the rate of change of the magnetic flux plays a role. If the change in the speed of the magnet is large enough, then the induction current will also be significant.

As a result of such experiments, the following regularities were revealed.

Rice. 3. What determines the magnetic flux and induction current

1. Magnetic flux is proportional to magnetic induction.

2. The magnetic flux is directly proportional to the surface area of ​​the circuit through which the lines of magnetic induction pass.

3. And the third - the dependence of the magnetic flux on the angle of the circuit. We have already paid attention to the fact that if the area of ​​the contour in one way or another, it affects the presence and magnitude of the magnetic flux.

Thus, we can say that the strength of the induction current is directly proportional to the rate of change of the magnetic flux.

∆ F is the change in the magnetic flux.

∆ t is the time during which the magnetic flux changes.

The ratio is just the rate of change of the magnetic flux.

Based on this dependence, we can conclude that, for example, an induction current can also be created by a fairly weak magnet, but the speed of movement of this magnet must be very high.

The first person who received this law was the English scientist M. Faraday. The concept of magnetic flux allows a deeper look at the unified nature of electrical and magnetic phenomena.

List of additional literature:

Elementary textbook of physics. Ed. G.S. Landsberga, T. 2. M., 1974 Yavorsky BM, Pinsky AA, Fundamentals of Physics, vol. 2., M. Fizmatlit., 2003 Do you know flows so well?// Kvant. - 2009. - No. 3. - S. 32-33. Aksenovich L. A. Physics in high school: Theory. Tasks. Tests: Proc. allowance for institutions providing general. environments, education / L. A. Aksenovich, N. N. Rakina, K. S. Farino; Ed. K. S. Farino. - Mn .: Adukatsy i vykhavanne, 2004. - P.344.

Lesson topic:

Discovery of electromagnetic induction. magnetic flux.

Target: introduce students to the phenomenon of electromagnetic induction.

During the classes

I. Organizational moment

II. Knowledge update.

1. Frontal survey.

• What is Ampère's hypothesis?
• What is magnetic permeability?
• What substances are called para- and diamagnets?
• What are ferrites?
• Where are ferrites used?
• How do you know that there is a magnetic field around the Earth?
• Where are the North and South magnetic poles of the Earth?
• What processes take place in the Earth's magnetosphere?
• What is the reason for the existence of a magnetic field near the Earth?

2. Analysis of experiments.

Experiment 1

The magnetic needle on the stand was brought to the lower and then to the upper end of the tripod. Why does the arrow turn to the lower end of the tripod from either side with the south pole, and to the upper end - the north end?(All iron objects are in the Earth's magnetic field. Under the influence of this field, they are magnetized, and the lower part of the object detects the north magnetic pole, and the top - the south.)

Experiment 2

In a large cork stopper, make a small groove for a piece of wire. Lower the cork into the water, and put the wire on top, placing it along the parallel. In this case, the wire, together with the cork, is rotated and installed along the meridian. Why?(The wire has been magnetized and is set in the Earth's field like a magnetic needle.)

III. Learning new material

There are magnetic forces between moving electric charges. Magnetic interactions are described based on the concept of a magnetic field that exists around moving electric charges. Electric and magnetic fields are generated by the same sources - electric charges. It can be assumed that there is a connection between them.

In 1831, M. Faraday confirmed this experimentally. He discovered the phenomenon of electromagnetic induction (slides 1.2).

Experiment 1

We connect the galvanometer to the coil, and we will put forward a permanent magnet from it. We observe the deviation of the galvanometer needle, a current (induction) has appeared (slide 3).

The current in the conductor occurs when the conductor is in the area of ​​\u200b\u200bthe alternating magnetic field (slide 4-7).

Faraday represented an alternating magnetic field as a change in the number of lines of force penetrating the surface bounded by a given contour. This number depends on the induction AT magnetic field, from the contour area S and its orientation in the given field.

F \u003d BS cos a - magnetic flux.

F [Wb] Weber (slide 8)

The induction current can have different directions, which depend on whether the magnetic flux penetrating the circuit decreases or increases. The rule for determining the direction of the induced current was formulated in 1833. E. X. Lenz.

Experiment 2

We slide a permanent magnet into a light aluminum ring. The ring is repelled from it, and when extended, it is attracted to the magnet.

The result does not depend on the polarity of the magnet. Repulsion and attraction is explained by the appearance of an induction current in it.

When the magnet is pushed in, the magnetic flux through the ring increases: the repulsion of the ring at the same time shows that the induction current in it has such a direction in which the induction vector of its magnetic field is opposite in direction to the induction vector of the external magnetic field.

Lenz's rule:

The inductive current always has such a direction that its magnetic field prevents any changes in the magnetic flux that cause the appearance of an inductive current.(slide 9).

IV. Conducting laboratory work

Laboratory work on the topic "Experimental verification of the Lenz rule"

Devices and materials:milliammeter, coil-coil, arcuate magnet.

Working process

1. Prepare a table.

« Physics - Grade 11 "

Electromagnetic induction

The English physicist Michael Faraday was confident in the unified nature of electrical and magnetic phenomena.
A time-varying magnetic field generates an electric field, and a changing electric field generates a magnetic field.
In 1831, Faraday discovered the phenomenon of electromagnetic induction, which formed the basis for the device of generators that convert mechanical energy into electric current energy.

The phenomenon of electromagnetic induction

The phenomenon of electromagnetic induction is the occurrence of an electric current in a conducting circuit, which either rests in a magnetic field that changes in time, or moves in a constant magnetic field in such a way that the number of magnetic induction lines penetrating the circuit changes.

For his numerous experiments, Faraday used two coils, a magnet, a switch, a direct current source and a galvanometer.

An electric current can magnetize a piece of iron. Can a magnet cause an electric current?

As a result of experiments, Faraday found main features phenomena of electromagnetic induction:

one). induction current occurs in one of the coils at the moment of closing or opening the electrical circuit of the other coil, which is motionless relative to the first one.

2) induction current occurs when the current strength in one of the coils changes with the help of a rheostat 3). induced current occurs when the coils move relative to each other 4). induction current occurs when a permanent magnet moves relative to the coil

Conclusion:

In a closed conducting circuit, a current arises when the number of magnetic induction lines penetrating the surface bounded by this circuit changes.
And the faster the number of lines of magnetic induction changes, the greater the resulting induction current.

It doesn't matter though. which is the reason for the change in the number of lines of magnetic induction.
This may also be a change in the number of lines of magnetic induction penetrating the surface bounded by a fixed conducting circuit, due to a change in the current strength in the adjacent coil,

and a change in the number of induction lines due to the movement of the circuit in an inhomogeneous magnetic field, the density of lines of which varies in space, etc.

magnetic flux

magnetic flux- this is a characteristic of the magnetic field, which depends on the vector of magnetic induction at all points of the surface bounded by a flat closed contour.

There is a flat closed conductor (circuit) bounding the surface with area S and placed in a uniform magnetic field.
The normal (vector whose modulus is equal to one) to the plane of the conductor makes an angle α with the direction of the magnetic induction vector

The magnetic flux Ф (flux of the magnetic induction vector) through a surface with an area S is a value equal to the product of the modulus of the magnetic induction vector by the area S and the cosine of the angle α between the vectors and:

Ф = BScos α

where
Bcos α = B n- projection of the magnetic induction vector on the normal to the contour plane.
So

Ф = B n S

The magnetic flux is greater, the more In n and S.

The magnetic flux depends on the orientation of the surface that the magnetic field penetrates.

The magnetic flux can be graphically interpreted as a quantity proportional to the number of lines of magnetic induction penetrating a surface with an area S.

The unit of magnetic flux is weber.
Magnetic flux in 1 weber ( 1 Wb) is created by a uniform magnetic field with an induction of 1 T through a surface of 1 m 2 located perpendicular to the magnetic induction vector.

Lesson summary on the topic:

"Magnetic field induction".

The purpose of the lesson: introduce the concept of magnetic field induction in accordance with the answer plan about the physical quantity.

Educational objectives of the lesson:

1. form a correct understanding of the vector of magnetic induction, as a power characteristic of the magnetic field;
2. enter the unit of magnetic induction;
3. form a correct idea of ​​the direction of magnetic induction and a graphical representation of magnetic fields.

Developing tasks of the lesson:

1. establish the relationship between theory and experiment in the study of phenomena;
2. further development of skills to analyze and draw conclusions;
3. maintain interest in the subject when setting up experiments.

Educational tasks of the lesson:

1. fostering a sense of sociability, goodwill and the ability to listen to each other.

Skills acquired by students:compare the results of experiments, observe, analyze, generalize and draw conclusions, explain physical phenomena, solve problems, develop oral speech.

Technical and software training tools:interactive whiteboard, personal computer, multimedia projector, Microsoft Power Point presentation program, presentation "Magnetic field induction", video clips "Earth's magnetic field", "Magnetic storms".

Equipment: worksheets, strip and arc magnets, conductors, current source, key, tripod, iron filings.

During the classes:

1. Organizational moment.

2. Statement of the question using the video fragment "Magnetic field of the Earth".

The power of modern science amazes even the inexperienced mind: it has split the atomic nucleus, reached the far corners of the universe, discovered the laws of the universe. But whether we like it or not, the future fate of mankind depends on the magnetic interaction of the Sun and the Earth.

Show video clip. Issues discussed:

1. What is the reason for the existence of the earth's magnetic field?
2. How does the sun affect the earth?
3. What is the role of the Earth's magnetic field in interaction with the Sun?

Today, every person should have a competent understanding of the essence of the physical processes on which his life depends.

3. Comprehensive testing of students' knowledge.So, let's systematize the knowledge that we have on the topic: "Magnetic field".

"The thinking mind does not feel happy until it succeeds in tying together the disparate facts it observes." Hevesy.

Frontal survey + individual answers on the description and demonstration of classical experiments on this topic.

1. What is a magnetic field?
2. What generates a magnetic field?
3. Who first discovered the magnetic field around a conductor with current?
4. Demonstrate Oersted's experience.
5. How is a magnetic field represented graphically?
6. How to get a picture of magnetic lines using iron filings? Show it by experience.
7. What are the magnetic lines of a straight conductor, a solenoid and a permanent magnet?
8. How to experimentally detect the presence of a force acting on a current-carrying conductor in a magnetic field?
9. How to determine the direction of this force?
10. State the left hand rule.

4. Checking homework. Exercise 36.

5.Updating knowledge.

What do you think, what determines how strong the interaction of a permanent magnet and a conductor with current will be? What are the assumptions?

"Undoubtedly all our knowledge begins with experience." (Immanuel Kant).Check on experience.

Experience: find out which of the magnets offered to you has a stronger effect on iron objects.

Thus, one should introduce a value that would characterize the magnetic field and show the force with which it acts on a current-carrying conductor, iron objects, and moving charged particles. This value is called the magnetic field induction.

Lesson objectives: to characterize the induction of the magnetic field according to the plan:

1. Definition of a physical quantity;
2. Symbol;
3. Calculation formula;
4. Direction;
5. Units.

6. Explanation of new material.In the course of the lesson, the guys fill out the worksheets, as a result they receive a reference summary on this topic.

Experience: interaction of a permanent arcuate magnet and a current-carrying conductor.

Purpose: to find out what determines the strength of the interaction?

Conclusion: magnetic force. interaction depends on the magnetic field, the current strength and the length of the conductor.

F/IL=const B=F/IL B - magnetic induction

Conclusion: Magnetic induction is the power characteristic of a magnet. fields. The greater the modulus of magnetic induction at a given point, the more force the field will act on a current-carrying conductor or a moving charge.

Magnetic induction - the power characteristic of a magnetic field, the module of which is equal to the ratio of the module of the force with which the field acts on a perpendicular magnet. lines a conductor with current, to the strength of the current and the length of the conductor.

Units of measurement 1Tl=1N/A*m, tesla. The units of measurement are named after the Serbian electrical engineer Nikola Tesla, whose photo is shown on the slide.

Magnetic induction is a vector quantity.Conclusion: It is directed tangentially to the magnetic lines.I remind you that the direction of the magnetic lines is determined by the right hand rule.Direction of magnet. induction indicates the north pole of the magnetic needle.Then a more precise definition of magnetic lines can be given as follows: these are lines, at each point of which the tangents coincide with the vector of magnetic induction.

Since the magnetic field arises around conductors with different current configurations, despite the fact that the magnetic lines are always closed, they can have different configurations. Therefore, magnetic fields are classified into homogeneous and inhomogeneous. Magnetic lines of uniform fields are located at the same distance from each other and have the same direction. In the figures, indicate the vectors of the magn. by induction, noting that they too must have the same direction and the same length.

Conclusion: A magnetic field is called homogeneous if at all its points the magnetic induction is the same both in magnitude and in direction.

7. Checking students' understanding of new knowledge.

Answer the questions:

1. What is the strength of a magnetic field called?
2. How is it designated?
3. What formula is used to calculate the modulus of magnetic induction?
4. Can we say that the magnet. induction depends on the strength with which the magnet. the field acts on a current-carrying conductor, the current strength, the length of the conductor?
5. What is the unit of measure for magnetic induction called?
6. According to the figures in the textbook 120,121,122 (p. 159), determine which fields are homogeneous and which are not.
7. Is the earth's magnetic field uniform?

8. Consolidation of students' knowledge

Run a practice test:

Option 1:

1. When electric charges are at rest, around them is found ....

2. How are iron filings arranged in a direct current magnetic field?

A. randomly B. in circles surrounding the conductor

3. Which pole of the magnetic needle indicates the direction of the magnetic induction vector?

A. northern B. southern

A. yes B. no

5. What determines the force with which the magnetic field acts on a current-carrying conductor?

A.Conductor cross-sectional area

B. magnetic induction

V.current

G. the time of the influence of the magnetic field on the conductor

D.conductor length

Option 2:

1. When electric charges move, then there is (s) around them

A. electric field B. magnetic field

B. electric and magnetic fields

2. What are the magnetic lines of a coil with current?

A. closed curves B. straight lines

B. randomly spaced lines

3. In what units is the magnetic field induction measured?

A. Newton B. Ampere V. Tesla

4. Is the magnetic field shown in the figure uniform?

A. yes B. no

5. How is the magnetic induction vector directed?

A. tangential to magnetic lines B. tangential to a current-carrying conductor

Check your desk mate: Option 1: 1-A, 2-B, 3-A, 4-A, 5-BVD

Option 2: 1-C,2-A,3-C,4-B,5-A

9. Homework:§46, orally answer the questions after the paragraph, exercise: 37 (in writing).

10. The results of the lesson.

1. What did you learn new? What have you learned?
2. What did you find especially difficult?
3. What material generated the most interest?

The stream of charged particles flying from the Sun reaches the Earth in 8 minutes. This leads to a change in the Earth's magnetic field, to the so-called magnetic storms. At this point, people experience a sharp jump in blood pressure. On the day of a solar flare, the number of cardiovascular diseases increases. There are even changes in the blood. The composition of the blood includes positive and negative ions, and the magnetic field just affects the charged particles. The changing magnetic the field disorients charged blood particles, increasing its lethargy.

Muscle loads, physical education and sports will help to adapt to adverse environmental changes. There is an improvement in blood circulation, oxygen supply to all organs, an increase in the body's resistance to changes in the Earth's magnetosphere.

One philosopher was asked: "What is the most important thing in life: wealth or fame?" The sage replied: “Neither wealth nor fame makes a person happy. Health is one of the most important sources of happiness and joy.” What do you wish!

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Lesson Objectives:

• Educational- to reveal the essence of the phenomenon of electromagnetic induction; explain to students the Lenz rule and teach them how to use it to determine the direction of the induction current; explain the law of electromagnetic induction; teach students to calculate the EMF of induction in the simplest cases.
• Educational- to develop the cognitive interest of students, the ability to think logically and generalize. Develop motives for teaching and interest in physics. Develop the ability to see the connection between physics and practice.
• Educational- to cultivate a love for student work, the ability to work in groups. Foster a culture of public speaking.

Equipment:

• Textbook "Physics - 11" G.Ya.Myakishev, B.B.Bukhovtsev, V.M.Charugin.
• G.N. Stepanova.
• "Physics - 11". Lesson plans for the textbook by G.Ya. Myakishev, B.B. Bukhovtsev. author - compiler G.V. Markin.
• Computer and projector.
• Material "Library of visual aids".
• Presentation for the lesson.

Lesson plan:

Lesson stages	Time min.	Methods and techniques
1. Organizational moment: Introduction Historical information		Message by the teacher of the topic, goals and objectives of the lesson. slide 1. Life and work of M. Faraday. (Student's message). Slides 2, 3, 4.
2. Explanation of new material Definition of the concepts "electromagnetic induction", "induction current". Introduction of the concept of magnetic flux. Connection of magnetic flux with the number of induction lines. Units of magnetic flux. Rule of E.H. Lenz. Study of the dependence of the induction current (and induction EMF) on the number of turns in the coil and the rate of change of the magnetic flux. Application of EMR in practice.		1. Demonstration of experiments on EMR, analysis of experiments, viewing the video clip "Examples of electromagnetic induction", Slides 5, 6. 2. Conversation, viewing the presentation. Slide 7. 3. Demonstration of the validity of the Lenz rule. Video clip "Lenz's Rule". Slides 8, 9. 4. Work in notebooks, making drawings, working with a textbook. 5. Conversation. Experiment. Watching the video fragment "Law of electromagnetic induction". Viewing a presentation. Slides 10, 11. 6. View presentation Slide 12.
3. Consolidation of the studied material	10	1. Solving problems No. 1819,1821 (1.3.5) (Collection of problems in physics 10-11. G.N. Stepanova)
4. Summing up	2	2. Generalization of the studied material by students.
5. Homework	1	§ 8-11 (to teach), R. No. 902 (b, d, e), 911 (in writing in notebooks)

DURING THE CLASSES

I. Organizational moment

1. Electric and magnetic fields are generated by the same sources - electric charges. Therefore, it can be assumed that there is a certain relationship between these fields. This assumption found experimental confirmation in 1831 in the experiments of the outstanding English physicist M. Faraday, in which he discovered the phenomenon of electromagnetic induction. (slide 1) .

Epigraph:

"Fluke
falls on only one share
prepared mind.

L.Pasternak

2. Brief historical essay on the life and work of M. Faraday. (Student's message). (Slides 2, 3).

II. For the first time, the phenomenon caused by an alternating magnetic field was observed in 1831 by M. Faraday. He solved the problem: Can a magnetic field cause an electric current to flow in a conductor? (Slide 4).

Electric current, argued M. Faraday, can magnetize a piece of iron. Could a magnet in turn cause an electric current? For a long time, this connection could not be found. It was difficult to think of the main thing, namely: a moving magnet, or a changing magnetic field, can excite an electric current in a coil. (Slide 5).
(viewing the video clip "Examples of electromagnetic induction"). (Slide 6).

Questions:

1. What do you think causes the electric current to flow in the coil?
2. Why was the current short?
3. Why is there no current when the magnet is inside the coil (Figure 1), when the rheostat slider does not move (Figure 2), when one coil stops moving relative to the other?

Conclusion: current appears when the magnetic field changes.

The phenomenon of electromagnetic induction consists in the occurrence of an electric current in a conducting circuit, which either rests in a magnetic field that changes in time, or moves in a constant magnetic field in such a way that the number of magnetic induction lines penetrating the circuit changes.
In the case of a changing magnetic field, its main characteristic B - the magnetic induction vector can change in magnitude and direction. But the phenomenon of electromagnetic induction is also observed in a magnetic field with a constant V.

Question: What is it that changes?

The area that the magnetic field penetrates changes, i.e. the number of lines of force that permeate this area changes.

To characterize the magnetic field in a region of space, a physical quantity is introduced - magnetic flux - F(Slide 7).

magnetic flux F through a surface area S call a value equal to the product of the modulus of the magnetic induction vector AT To the square S and cosine of the angle between the vectors AT and n.

F \u003d BS cos

Work B cos = B n is the projection of the magnetic induction vector onto the normal n to the contour plane. So F \u003d B n S.

Magnetic flux unit - Wb(Weber).

A magnetic flux of 1 weber (Wb) is created by a uniform magnetic field with an induction of 1 T through a surface of 1 m 2 located perpendicular to the magnetic induction vector.
The main thing in the phenomenon of electromagnetic induction is the generation of an electric field by an alternating magnetic field. A current appears in a closed coil, which makes it possible to register the phenomenon (Figure 1).
The resulting inductive current of one direction or another somehow interacts with the magnet. A coil with a current flowing through it is like a magnet with two poles - north and south. The direction of the induced current determines which end of the coil acts as the north pole. Based on the law of conservation of energy, it is possible to predict in which cases the coil will attract the magnet, and in which cases it will repel.
If the magnet is brought closer to the coil, then an induction current of this direction appears in it, the magnet is necessarily repelled. To bring the magnet closer to the coil, positive work must be done. The coil becomes similar to a magnet, turned with the same pole to the magnet approaching it. Like poles repel each other. Removing the magnet is the opposite.

In the first case, the magnetic flux increases (Figure 5), and in the second case it decreases. Moreover, in the first case, the lines of induction B / of the magnetic field created by the induction current that has arisen in the coil come out of the upper end of the coil, because the coil repels the magnet, and in the second case they enter this end. These lines are shown in darker color in the figure. In the first case, the coil with current is similar to a magnet, the north pole of which is above, and in the second case, below.
Similar conclusions can be drawn using the experience shown in the figure (Figure 6).

(View excerpt "Lenz's Rule")

Conclusion: The inductive current arising in a closed circuit counteracts the change in the magnetic flux by which it is caused by its magnetic field. (Slide 8).

Lenz's rule. The induction current always has a direction in which there is a counteraction to the causes that generated it.

Algorithm for determining the direction of the induction current. (Slide 9)

1. Determine the direction of the lines of induction of the external field B (they leave N and enter S).
2. Determine whether the magnetic flux through the circuit increases or decreases (if the magnet moves into the ring, then ∆Ф> 0, if it moves out, then ∆Ф<0).
3. Determine the direction of the lines of induction of the magnetic field B′ created by the induction current (if ∆Ф>0, then the lines В and В′ are directed in opposite directions; if ∆Ф<0, то линии В и В′ сонаправлены).
4. Using the gimlet rule (right hand), determine the direction of the induction current.
Faraday's experiments showed that the strength of the inductive current in a conducting circuit is proportional to the rate of change in the number of magnetic induction lines penetrating the surface bounded by this circuit. (Slide 10).
With any change in the magnetic flux through a conducting circuit, an electric current arises in this circuit.
The induction emf in a closed loop is equal to the rate of change of the magnetic flux through the area bounded by this loop.
The current in the circuit has a positive direction when the external magnetic flux decreases.

(View snippet "Law of Electromagnetic Induction")

(Slide 11).

The EMF of electromagnetic induction in a closed loop is numerically equal and opposite in sign to the rate of change of the magnetic flux through the surface bounded by this loop.

The discovery of electromagnetic induction made a significant contribution to the technical revolution and served as the basis of modern electrical engineering. (Slide 12).

III. Consolidation of the studied

Solving problems No. 1819, 1821(1.3.5)

(Collection of problems in physics 10-11. G.N. Stepanova).

IV. Homework:

§eight - 11 (to teach), R. No. 902 (b, d, f), No. 911 (in writing in notebooks)

Bibliography:

1. Textbook "Physics - 11" G.Ya.Myakishev, B.B.Bukhovtsev, V.M.Charugin.
2. Collection of problems in physics 10-11. G.N. Stepanova.
3. "Physics - 11". Lesson plans for the textbook by G.Ya. Myakishev, B.B. Bukhovtsev. author-compiler G.V. Markina.
4. V / m and video materials. School physical experiment "Electromagnetic induction" (sections: "Examples of electromagnetic induction", "Lenz's Rule", "Law of electromagnetic induction").
5. Collection of problems in physics 10-11. A.P. Rymkevich.