Lesson summary “Magnetic flux. Electromagnetic induction

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Lesson objectives:

• Educational– reveal the essence of the phenomenon of electromagnetic induction; Explain to students Lenz’s rule and teach them to use it to determine the direction of the induction current; explain the law of electromagnetic induction; teach students to calculate induced emf in the simplest cases.
• Developmental– develop students’ cognitive interest, ability to think logically and generalize. Develop motives for learning and interest in physics. Develop the ability to see the connection between physics and practice.
• Educational– cultivate a love of 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. Markina.
• Computer and projector.
• Material "Library of Visual Aids".
• Presentation for the lesson.

Lesson plan:

Lesson steps	Time min.	Methods and techniques
1. Organizational moment: Introduction Historical information		The teacher’s message about the topic, goals and objectives of the lesson. Slide 1. Life and work of M. Faraday. (Student 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. Relationship between magnetic flux and the number of induction lines. Units of magnetic flux. E.H. Lenz's rule. Study of the dependence of induced current (and induced emf) on the number of turns in the coil and the rate of change of magnetic flux. Application of EMR in practice.		1. Demonstration of experiments on EMR, analysis of experiments, viewing of the video fragment “Examples of electromagnetic induction”, Slides 5, 6. 2. Conversation, viewing of the presentation. Slide 7. 3. Demonstration of the validity of Lenz's rule. Video fragment “Lenz's Rule”. Slides 8, 9. 4. Work in notebooks, make drawings, work with a textbook. 5. Conversation. Experiment. Watch the video clip “The Law of Electromagnetic Induction.” View the presentation. Slides 10, 11. 6. View the presentation Slide 12.
3. Consolidation of the studied material	10	1. Solution of problems No. 1819,1821(1.3.5) (Collection of problems in physics 10-11. G.N. Stepanova)
4. Summing up	2	2.Summarization of the studied material by students.
5. Homework	1	§ 8-11 (teach), R. No. 902 (b, d, f), 911 (written in notebooks)

DURING THE CLASSES

I. Organizational moment

1. Electric and magnetic fields are generated by the same sources - electric charges. Therefore, we can make the assumption that there is a certain connection 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 only on one share
prepared mind."

L. Pasternak

2. A brief historical sketch of the life and work of M. Faraday. (Student message). (Slides 2, 3).

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

Electric current, M. Faraday reasoned, can magnetize a piece of iron. Couldn't a magnet, in turn, cause an electric current? For a long time this connection could not be discovered. It was difficult to figure out the main thing, namely: a moving magnet, or a changing magnetic field, can excite an electric current in a coil. (Slide 5).
(watch the video “Examples of electromagnetic induction”). (Slide6).

Questions:

1. What do you think causes electric current to flow in the coil?
2. Why was the current short-lived?
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 is either at rest in a time-varying magnetic field 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 constant B.

Question: What changes?

The area pierced by the magnetic field changes, i.e. the number of lines of force that penetrate 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 quantity equal to the product of the magnitude of the magnetic induction vector IN To the square S and cosine of the angle between the vectors IN And n.

Ф = ВS cos

Work V cos = V n represents the projection of the magnetic induction vector onto the normal n to the contour plane. That's why Ф = В 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 with an area 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 arises in a closed coil, which allows the phenomenon to be recorded (Figure 1).
The resulting induced current of one direction or another somehow interacts with the magnet. A coil with current passing through it is like a magnet with two poles - north and south. The direction of the induction current determines which end of the coil acts as the north pole. Based on the law of conservation of energy, we can predict in which cases the coil will attract the magnet and in which it will repel it.
If the magnet is brought closer to the coil, then an induced current appears in it in this direction; the magnet is necessarily repelled. To bring the magnet and coil closer together, positive work must be done. The coil becomes like a magnet, with its pole of the same name facing the magnet approaching it. Like poles repel each other. When removing the magnet, it's 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 induction lines B/ of the magnetic field created by the induction current that arises in the coil come out from 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 colors in the figure. In the first case, the coil with current is similar to a magnet, the north pole of which is located at the top, and in the second case, at the bottom.
Similar conclusions can be drawn using the experiment shown in the figure (Figure 6).

(View fragment “Lenz's Rule”)

Conclusion: The induced current arising in a closed circuit with its magnetic field counteracts the change in the magnetic flux that it causes. (Slide 8).

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

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

1. Determine the direction of the induction lines 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 induction lines of the magnetic field B′ created by the induced current (if ∆Ф>0, then lines B and B′ 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 induced 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).
Whenever there is a change in the magnetic flux through a conducting circuit, an electric current arises in this circuit.
The induced emf in a closed loop is equal to the rate of change of the magnetic flux through the area limited by this loop.
The current in the circuit has a positive direction as the external magnetic flux decreases.

(View fragment “The 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 for modern electrical engineering. (Slide 12).

III. Consolidation of what has been learned

Solving problems No. 1819, 1821(1.3.5)

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

IV. Homework:

§8 - 11 (teach), R. No. 902 (b, d, f), No. 911 (written 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 physics 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.

PHYSICS LESSON. PREPARED BY PHYSICS TEACHER VITALY VASILIEVICH KAZAKOV.

Lesson topic: Magnetic flux

The purpose of the lesson

1.Introduce the definition of magnetic flux;

2.Develop abstract thinking;

3. Cultivate accuracy and precision.

Lesson objectives: Developmental

Lesson type: presentation of new material

Equipment: computer , LCD-projector , projectional th screen .

During the classes

1.Checking homework

1.What is the magnetic induction vector?

1.An axis passing through the center of a permanent magnet;

2. Strength characteristics of the magnetic field;

3. Magnetic field lines of a straight conductor.

2. Magnetic induction vector...

2.comes out from the south pole of a permanent magnet;

3. 1. Select the correct statement(s).

A: magnetic lines are closed

B: magnetic lines are denser in those areas where the magnetic field is stronger

B: the direction of the field lines coincides with the direction of the north pole of the magnetic needle placed at the point being studied

Only A; 2. Only B; 3. A, B, and C.

4. The figure shows magnetic field lines. At what point in this field will the maximum force act on the magnetic needle?

1. 3; 2. 1; 3. 2.

5 . A straight conductor was placed in a uniform magnetic field perpendicular to the lines of magnetic induction, through which a current of force 8A flows. Determine the induction of this field if it acts with a force of 0.02 N for every 5 cm of the length of the conductor.

1. 0.05 T 2. 0.0005 T 3. 80 T 4. 0.0125 T

Answers: 1-2; 2-3; 3-3; 4-2; 5-1.

2.Learning something new

Statement of a virtual problem.

We came to the next plow festival - Sabantuy. But here, it would seem, was a disappointment - the rain poured down. I offer you a competition game in which you need to collect as much water as possible in buckets. (The condition is to collect only rain falling from the sky). The students have a heated discussion about who will collect water how: - they would run against the rain; - preferably more dishes; - stand in one place; - run to where the rain is heavier; - keep the bucket perpendicular to the rain. These examples are irrefutable. The children themselves came to fulfill the goal of the lesson - determining magnetic flux. All that remains is to draw conclusions and come to mathematical formulations. So, magnetic flux (rain) depends on:- surface area of ​​the contour (bucket); - magnetic induction vector (rain intensity); - the angle between the magnetic induction vector and the normal to the contour plane.

Consolidation

Now let’s consolidate our conclusions with interactive models

2.Tutorial: Peryshkin A.V., Gutnik E.M. Physics. 9th grade: Textbook for general education institutions. M.: Bustard, 2009.

3. Physics. 9th grade Lesson plans for textbooks Peryshkina A.V. and Gromova S.V_2010 -364s

4. Physics tests for the textbookPeryshkin A.V., Gutnik E.M. Physics. 9th grade

LESSON PLAN

Topic: “Magnetic flux. The phenomenon of electromagnetic induction", 9th grade

Lesson objectives:

The goal is to achieve educational results.

Personal results:

– development of cognitive interests, intellectual and creative abilities;

– independence in acquiring new knowledge and practical skills;

– formation of value attitudes towards learning outcomes.

Meta-subject results:

– mastering the skills of independently acquiring new knowledge, organizing educational activities, setting goals, planning;

– mastering methods of action in non-standard situations, mastering heuristic methods of problem solving;

– developing the skills to observe, highlight the main thing, and explain what is seen.

Subject results:

– know: magnetic flux, induced current, the phenomenon of electromagnetic induction;

– understand: concept of flux, phenomenon of electromagnetic induction

– be able to: determine the direction of the induction current, solve typical OGE problems.

Lesson type: learning new material

Lesson format: lesson study

Technologies: elements of critical thinking technology, problem-based learning, ICT, problem-based dialogue technology

Lesson equipment: computer, interactive whiteboard, coil, tripod with foot, strip magnet – 2 pcs., demonstration galvanometer, wires, device for demonstrating Lenz’s rule.

During the classes

Start: 10.30

1. Organizational stage (5 minutes).

Hello guys! Today I will teach a physics lesson, my name is Innokenty Innokentyevich Malgarov, a physics teacher at the Kyllakh school. I am very glad to work with you, with the high school students, I hope today’s lesson will proceed in a productive manner. Today's lesson assesses attentiveness, independence, and resourcefulness. The motto of our lesson is “Everything is very simple, you just need to understand!” Now, your desk neighbors look at each other, wish them luck and shake hands. To establish feedback, I will sometimes clap my hands and you will repeat. Shall we check? Amazing!

Please look at the screen. What do we see? That's right, a waterfall and strong wind. What word (one!) unites these two natural phenomena? Yes, flow. Water flow and air flow. Today we will also talk about flow. Only about a flow of a completely different nature. Can you guess what? What are the topics you covered previously related to? That's right, with magnetism. Therefore, write down the topic of the lesson in your worksheets: Magnetic Flux. The phenomenon of electromagnetic induction.

Start: 10.35

2. Updating knowledge (5 minutes).

Exercise 1. Please look at the screen. What can you say about this drawing? The blanks in the worksheets should be filled in. Consult your partner.

1. A current-carrying conductor occurs around a magnetic field. It is always closed;

2. The strength characteristic of the magnetic field is magnetic induction vector 0 " style="border-collapse:collapse;border:none">

Look at the screen. By analogy, fill in the second column for the circuit in a magnetic field.

Please take a look at the demo table. On the table you see a stand with a movable rocker with two aluminum rings. One is whole, and the other has a slot. We know that aluminum does not exhibit magnetic properties. We begin to insert the magnet into the ring with the slot. Nothing happens. Now let's start introducing the magnet into the whole ring. Please note that the hundred ring begins to “run away” from the magnet. Stop the movement of the magnet. The ring also stops. Then we begin to carefully remove the magnet. The ring now begins to follow the magnet.

Try to explain what you saw (students try to explain).

Please look at the screen. There's a hint hidden here. (Students come to the conclusion that when the magnetic flux changes, an electric current can be obtained).

Task 4. It turns out that if you change the magnetic flux, you can get an electric current in the circuit. You already know how to change the flow. How? That's right, you can strengthen or weaken the magnetic field, change the area of ​​the circuit itself and change the direction of the circuit plane. Now I will tell you a story. Listen carefully and complete task 4 at the same time.

In 1821, the English physicist Michael Faraday, inspired by the work of Oersted (the scientist who discovered the magnetic field around a current-carrying conductor), set himself the task of obtaining electricity from magnetism. For almost ten years he carried wires and magnets in his trouser pocket, unsuccessfully trying to generate an electric current from them. And one day, completely by accident, on August 28, 1831, he succeeded. (Prepare and show a demonstration). Faraday discovered that if a coil is quickly placed on a magnet (or removed from it), a short-term current arises in it, which can be detected using a galvanometer. This phenomenon came to be called electromagnetic induction.

This current is called induced current. We said that any electric current generates a magnetic field. Induction current also creates its own magnetic field. Moreover, this field interacts with the field of a permanent magnet.

Now, using the interactive whiteboard, determine the direction of the induction current. What conclusion can be drawn regarding the direction of the magnetic field of the induced current?

Start: 11.00

5. Application of knowledge in various situations (10 minutes).

I suggest you solve the tasks that are offered in the OGE in physics.

Task 5. A strip magnet is brought to a solid aluminum ring suspended on a silk thread at a constant speed (see figure). What will happen to the ring during this time?

1) the ring will remain at rest

2) the ring will be attracted to the magnet

3) the ring will be repelled by the magnet

4) the ring will begin to rotate around the thread

Task 6.

1) Only at 2.

2) Only in 1.

4) Only at 3.

Start: 11.10

5. Reflection (5 minutes).

It's time to evaluate the results of our lesson. What new have you learned? Have the goals set at the beginning of the lesson been achieved? What was difficult for you? What did you especially like? What feelings did you experience?

6. Information about homework

Find in your textbooks the topic “Magnetic flux”, “The phenomenon of electromagnetic induction”, read and see if you can answer the self-test questions.

Thank you again for your cooperation, for your interest and, in general, for a very interesting lesson. I wish to study physics well and, on its basis, to understand the structure of the world.

“It’s very simple, you just need to understand!”

Last name, first name of the student ________________________________________________ 9th grade student

Date "____"________________2016

WORKSHEET

Lesson topic:__________________________________________________________________________

__________________________________________________________________________

644 " style="width:483.25pt;border-collapse:collapse;border:none">

Task 4. Fill the gaps.

1. The phenomenon of the occurrence of current in a closed conductor (circuit) when the magnetic field penetrating this circuit changes is called _______________________;

2. The current that arises in the circuit is called ___________________________;

3. The magnetic field of the circuit created by the induction current will be directed __________________ the magnetic field of the permanent magnet (Lenz’s Rule).

https://pandia.ru/text/80/300/images/image006_55.jpg" align="left hspace=12" width="238" height="89"> Task 6. There are three identical metal rings. A magnet is removed from the first ring, a magnet is inserted into the second ring, and a stationary magnet is located in the third ring. In which ring does the induction current flow?

1) Only at 2.

2) Only in 1.

9.

Topic: Magnetic field induction. Magnetic flux

9th grade

Lesson duration – 45 minutes;

Use of information technology - projector.

Magnetic field induction. Magnetic flux

Lesson objectives:

Organize activities for perception, comprehension and primary memorization of new knowledge and methods of activity;

Create conditions for the development of memory and logical thinking;

Create conditions for instilling self-confidence in students through lessons;

Create conditions for the development of skills to use scientific methods of knowledge.

Lesson objectives:

Introduce the concept of magnetic field induction;

Enter the definition of magnetic flux.

During the classes

1. Organizational stage

2. Checking homework

3. Updating the subjective experience of students

Frontal survey(Slide 6)

How is a magnetic field represented graphically?

What are magnetic induction lines called?

What is the difference between a uniform magnetic field and an inhomogeneous one?

How is the existence of a magnetic field detected?

How to determine the direction of the force with which a magnetic field acts on a current-carrying conductor?

Formulate the left-hand rule.

4. Stage of learning new knowledge and ways of doing things

Some magnets create stronger fields in space than others (Slide 7 ).

The magnetic field is characterized by a vector physical quantity, which is denotedIN.

IN- magnetic field induction (magnetic induction).

Consider the experiment presented in the figure (Slide 8 )

The modulus of this force acting on a current-carrying conductor depends on: (Slide 9 ):

The magnetic field itself

Conductor lengths

Current strength

B = F/Il [ IN ] = [T]

This value is taken as the magnitude of the magnetic induction vector.IN depends only on the field and can serve as its quantitative characteristic.

By introducing a physical quantity such as magnetic induction, we can give a more accurate definition of magnetic field lines.

Magnetic induction lines are lines whose tangents at each point of the field coincide with the direction of the magnetic induction vector (Slide 10 ).

The magnetic field is calledhomogeneous , if at all its points the magnetic induction B is the same. Otherwise the field is calledheterogeneous ( Slide 11 ) .

2. A quantity characterizing the magnetic field - magnetic flux or flux of the magnetic induction vectorF .

With an increase in the magnetic induction vector inn times, the magnetic flux also increases by n once.

When the contour is enlarged in n times, the magnetic flux also increases by n once.

When the circuit is oriented perpendicular to the lines of magnetic induction, the magnetic flux is maximum; when the circuit is oriented parallel to the lines of magnetic induction, the magnetic flux is zero

( Slide 12-14 ).

Magnetic flux - Ф =BScosα , [F] = [Wb]( Slide 15 )

That. the magnetic flux penetrating the area of ​​the circuit changes when the module of the magnetic induction vector changes, the area of ​​the circuit and when the circuit rotates, i.e. when its orientation changes relative to the magnetic field lines.

5. Stage of initial verification of understanding of what has been learned

Questions:

1. What formula is used to calculate magnetic flux?

2. When is the magnetic flux passing through a closed circuit at its maximum? minimal? (Slide 16 ).

6. Stage of consolidation of what has been learned

Tasks:

1. Water in a stream and in a river flows at the same speed. In which case is the flow of water through a sieve placed perpendicular to the flow greater?

2. What is the induction of a magnetic field in which a force of 0.4 N acts on a 2 m conductor? The current in the conductor is 10 A.

3. Flat contour with an area of ​​20 cm 2 is in a uniform magnetic field with an induction of 0.5 T. Determine the magnetic flux penetrating the circuit if the normal to the circuit makes an angle of 60°C with the magnetic field induction vector (Slide 17 ).

7. Results, homework paragraph 46, 47,

ex. 37, 38( Slide 18 )

8. Reflection

Used Books

1. Peryshkin A.V. Physics. 8th grade. - M.: Bustard, 2009.

2. Gromov S.V., Rodina N.A. Physics. 9th grade - M.: Prosveshchenie, 2002.