PHYSICS LESSON. PREPARED BY PHYSICS TEACHER VITALY VASILIEVICH KAZAKOV.
Lesson topic: Magnetic flux
The purpose of the lesson
1. Enter the definition of magnetic flux;
2.Develop abstract thinking;
3. To cultivate accuracy, accuracy.
Lesson objectives: Developing
Type of lesson presentation of new material
Equipment: a computer , LCD-projector , projection th screen .
During the classes
1.Checking homework
1. What is the magnetic induction vector?
1. Axis passing through the center permanent magnet;
2. Power characteristic of the magnetic field;
3. Magnetic field lines of a straight conductor.
2. The vector of magnetic induction ...
2. comes out of the south pole of the permanent magnet;
3. 1. Choose the correct statement(s).
BUT: magnetic lines closed
B: magnetic lines are denser in areas where the magnetic field is stronger
B: direction lines of force coincides with the direction north pole magnetic needle placed at the point under study
Only A; 2. Only B; 3. A, B, and C.
4. The figure shows the magnetic field lines. At what point of 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 8A flows. Determine the induction of this field if it acts with a force of 0.02 N for every 5 cm of the conductor length.
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 a new
Statement of the virtual task.
We came to the next holiday of the plow - Sabantuy. But here, it would seem, chagrin - 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: - would run against the rain; - preferably more dishes; - stand in one place; - run to where the rain is stronger; - hold the bucket perpendicular to the rain. These examples are irrefutable. The children themselves came to fulfill the purpose of the lesson - the definition of the magnetic flux. It remains 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.
Anchoring
And now we fix our conclusions with interactive models
2.tutorial: Peryshkin A.V., Gutnik E.M. Physics. Grade 9: Textbook for educational institutions. M.: Bustard, 2009.
3. Physics. 9th grade Lesson Plans to the textbooks of Peryshkin A.V. and Gromova S.V_2010 -364s
4. Physics tests for the textbookPeryshkin A.V., Gutnik E.M. Physics. Grade 9
« 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 electromagnetic induction, which formed the basis for the device of generators that convert mechanical energy into energy electric current.
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 source direct current 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 electrical circuit another coil, fixed relative to the first.
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 homogeneous magnetic field with an induction of 1 T through a surface of 1 m 2 located perpendicular to the magnetic induction vector.
Back forward
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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 |
Methods and techniques |
| 1. Organizational moment: Introduction |
Message by the teacher of the topic, goals and objectives of the lesson. slide 1. |
|
| 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:
- What do you think causes the electric current to flow in the coil?
- Why was the current short?
- 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 like a magnet facing pole of the same name to an approaching magnet. 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 circuit is numerically equal and opposite in sign to the rate of change of the magnetic flux through the surface bounded by this circuit.
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:
- Textbook "Physics - 11" G.Ya.Myakishev, B.B.Bukhovtsev, V.M.Charugin.
- Collection of problems in physics 10-11. G.N. Stepanova.
- "Physics - 11". Lesson plans for the textbook by G.Ya. Myakishev, B.B. Bukhovtsev. author-compiler G.V. Markina.
- V / m and video materials. School physical experiment "Electromagnetic induction" (sections: "Examples of electromagnetic induction", "Lenz's Rule", "Law of electromagnetic induction").
- Collection of problems in physics 10-11. A.P. Rymkevich.