Slide 1
“Happy accidents come only to one portion of the prepared mind.” L. Pasternak The phenomenon of electromagnetic inductionSlide 2
“My greatest discovery was that of Faraday.” Humphry Davy Discovery of electromagnetic induction
Slide 3
1791 – 1867, English physicist, Honorary Member of the St. Petersburg Academy of Sciences (1830), Founder of the doctrine of the electromagnetic field; introduced the concepts of “electric” and “magnetic field”; expressed the idea of the existence of electromagnetic waves. 1821: “Convert magnetism into electricity.” 1931 - received electric current using a magnetic field Michael Faraday
Slide 4
August 29, 1831 “A copper wire 203 feet long was wound on a wide wooden spool, and between its turns was wound a wire of the same length, insulated from the first cotton thread. One of these spirals was connected to a galvanometer, the other to a strong battery... When the circuit was closed, a sudden but extremely weak action was observed on the galvanometer, and the same action was noticed when the current ceased. With the continuous passage of current through one of the spirals, it was not possible to detect deviations of the galvanometer needle ... "
Slide 5
Electric current arose when the conductor was in the area of action of an alternating magnetic field. October 17, 1831
Slide 6
Electromagnetic induction is a physical phenomenon consisting in the emergence of a vortex electric field that causes an electric current in a closed circuit when the flux of magnetic induction changes through the surface limited by this circuit. The current arising in this case is called induction.
Slide 7
Lenz's rule E.H. Lenz 1804 - 1865, academician, rector of St. Petersburg University Induction current always has a direction in which there is a counteraction to the reasons that gave rise to it.
Slide 8
Magnetic flux Ф through a surface of area S is a value equal to the product of the magnitude of the magnetic induction vector B by the area S and the cosine of the angle between vectors B and n. Ф=ВS cos Ф=Вn S Magnetic flux
Slide 9
∆Ф is characterized by a change in the number of lines B penetrating the contour. 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 ∆Ф0, then lines B and B′ are directed in opposite directions; if ∆Ф
The phenomenon of electromagnetic induction.
The phenomenon of electromagnetic induction is that when the magnetic flux changes through a closed circuit, an electric current arises in the latter.
1.Assemble the installation and obtain the induced current.
2.Answer the questions:
- What determines the direction of the induction current?
- How does a change in the magnetic flux through the coil affect the magnitude of the induced current?
a) on the magnitude of the change in magnetic flux;
b) on the direction of the magnetic field induction lines.
The magnitude of the induction current depends on the speed of change of the magnetic flux.
Self-induction.
L - inductance, H(henry )
The appearance of induction current in an electrical circuit when
change in current strength.
Application of the phenomenon of electromagnetic induction.
Induction currents arising in conductors are used to heat them. The design of electric furnaces for melting metals is based on this principle. The same effect is used in household microwave ovens.
These induction currents are called Foucault currents.
Transformer is a device for converting voltage.
1878 Yablochkov P.N. I.F. Usagin.
To reduce energy losses,
caused by Foucault currents in the transformer core, the core is laminated,
made from thin plates insulated from each other.
K = N 1 / N 2 – coefficient
transformation
Metal detector
Special detectors are used to detect metal objects. For example, at airports, a metal detector detects fields of induced currents in metal objects.
The magnetic field B 0 created by the current I 0 of the transmitting coil induces currents in metal objects that prevent changes in the magnetic flux. In turn, the magnetic field B ’ of these currents induces a current I ’ in the receiver coil, triggering an alarm signal.
Induction electromechanical alternating current generator.
The highest value of the alternating current is limited by inductance, i.e., the greater the inductance and frequency of the voltage, the lower the current value will be. Alternating current widely used in communication devices (radio, television, long-distance wire telephony, etc.).
Presentation on the topic "Electromagnetic induction. Faraday's experiments" in physics in powerpoint format. This presentation for schoolchildren tells how the phenomenon of electromagnetic induction was discovered, what this phenomenon is and what laws it has. Auto presentation: teacher Popova I.A.
Fragments from the presentation
Discovery of the phenomenon of electromagnetic induction
The phenomenon of electromagnetic induction was discovered by the outstanding English physicist M. Faraday in 1831. It consists in the occurrence of an electric current in a closed conducting circuit when the magnetic flux penetrating the circuit changes over time.
The phenomenon of electromagnetic induction
consists in the occurrence of an electric current in a closed conducting circuit when the magnetic flux penetrating the circuit changes over time.
Magnetic flux
- The magnetic flux Φ through the area S of the circuit is the quantity
- Φ = B S cos α
- where B is the magnitude of the magnetic induction vector,
- α – angle between the vector and the normal to the contour plane
- The SI unit of magnetic flux is called weber (Wb)
Faraday's law of electromagnetic induction
- Lenz's rule:
- When the magnetic flux changes in a conducting circuit, an induced emf Eind arises, equal to the rate of change of the magnetic flux through the surface bounded by the circuit, taken with a minus sign:
A change in the magnetic flux penetrating a closed circuit can occur for two reasons:
- The magnetic flux changes due to the movement of the circuit or its parts in a time-constant magnetic field.
- Change in time of the magnetic field with a stationary circuit.
conclusions
The phenomenon of electromagnetic induction is observed in the following cases:
- movement of the magnet relative to the coil (or vice versa);
- movement of the coils relative to each other;
- changing the current strength in the circuit of the first coil (using a rheostat or closing and opening a switch);
- rotation of the circuit in a magnetic field;
- rotation of the magnet inside the circuit.
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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 |
Methods and techniques |
| 1. Organizational point: Introduction |
The teacher’s message about 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. 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. | 10 | 3. Consolidation of the studied material |
| 1. Solution of problems No. 1819,1821(1.3.5) (Collection of problems in physics 10-11. G.N. Stepanova) | 2 | 4. Summing up |
| 2.Summarization of the studied material by students. | 1 | 5. Homework |
§ 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."
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:
- What do you think causes electric current to flow in the coil?
- Why was the current short-lived?
- 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 a magnet is brought closer to the coil, then an induced current of this direction appears in it, and 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:
- 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
- Collection of problems in physics 10-11. V/m and video materials. School physics experiment “Electromagnetic induction” (sections: “Examples of electromagnetic induction”, “Lenz’s rule”, “Law of electromagnetic induction”)..
A.P. Rymkevich
The phenomenon of electromagnetic induction
prepared mind."
“Happy accidents come only to one portion of the prepared mind.”
The experience of the Danish scientist Oersted
1820
1777 – 1851
Michael Faraday
1791 – 1867, English physicist,
Honorary member of the St. Petersburg
Academy of Sciences (1830),
Founder of the doctrine of the electromagnetic field; introduced the concepts of “electric” and “magnetic field”;
expressed the idea of existence .
1821 electromagnetic waves
1931 year: “Convert magnetism into electricity.”
year – received electric current using a magnetic field
"Electromagnetic induction" - Latin word meaning "
guidance"
M. Faraday's experiment
“A copper wire 203 feet long was wound on a wide wooden reel, and between its turns was wound a wire of the same length, insulated from the first with a cotton thread.
When the circuit was closed, a sudden but extremely weak action was observed on the galvanometer, and the same effect was observed when the current was stopped.
With the continuous passage of current through one of the spirals, it was not possible to detect deviations of the galvanometer needle ... "
What do we see?
Conclusion from the experience :
- The current arising in the coil (closed circuit) is called
induction.
- The difference between the resulting current and what we previously knew is that to receive it no power source needed.
Faraday's general conclusion
Induction current in a closed loop occurs when the magnetic flux changes through the area limited by the loop.
Electromagnetic induction is a physical phenomenon consisting 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.
The current that arises is called induction .
What is the reason for the occurrence induced current in the coil?
Consider a magnet:
What can you say about the magnet?
When we introduce a magnet into the closed circuit of a coil, What changes for him?
How to determine the direction of the induction current?
We see that the direction of the induction current is different in these experiments.
Based on the law of conservation of energy, the Russian scientist Lenz offered rule , which determines the direction of the induction current.
Russian physicist Emil Lenz
1804 – 1865
0, if it extends, 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, then lines B and B′ are co-directed). 4. Using the gimlet rule (right hand), determine the direction of the induction current. ∆ Ф is characterized by a change in the number of lines of magnetic induction B penetrating the circuit "width="640" 1. Determine the direction of the induction lines of the external field B (coming from N and are included in S ).
2. Determine whether the magnetic flux through the circuit increases or decreases (if the magnet moves into the ring, then ∆Ф 0, if extended, then ∆Ф 0).
3. Determine the direction of the induction lines of the magnetic field B′ created by the induction current (if ∆Ф 0, then lines B and B′ are directed in opposite directions; if ∆Ф 0, then lines B and B′ are codirectional).
4. Using the gimlet rule (right hand), determine the direction of the induction current.
∆ F
characterized by change
number of lines of magnetic induction B,
permeating the contour
Mathematical formula for the law of electromagnetic induction
ε = - ΔΦ/Δ t
ΔΦ/Δ t - rate of change of magnetic flux (units Wb/s )
The induced emf in a closed loop is equal in magnitude to the rate of change of the magnetic flux through the surface bounded by the loop.
Electromagnetic law induction
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 current in the circuit has a positive direction as the external magnetic flux decreases.
Computer hard drive.
Electromagnetic induction in the modern world
Video recorder.
Policeman detector.
Metal detector at airports
Magnetic levitation train
Showing videos about the application of the phenomenon of electromagnetic induction: metal detector, recording information on magnetic media and reading from them - disk “Physics grades 7-11. Library of visual aids" Educational complexes.