Goal of the work: experimental study of the phenomenon of magnetic induction verification of Lenz's rule.
Theoretical part:
Phenomenon 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 our case, it would be more reasonable to change the magnetic field in time, since it is created by a moving (freely) magnet. According to Lenz's rule, the inductive current that occurs in a closed circuit counteracts with its magnetic field the change in the magnetic flux by which it is caused. In this case, we can observe this by the deviation of the milliammeter needle.
Equipment: Milliammeter, power supply, coils with cores, arcuate magnet, push-button switch, connecting wires, magnetic needle (compass), rheostat.
Work order
I. Finding out the conditions for the occurrence of induction current.1. Connect the coil-coil to the clamps of the milliammeter.
2. Observing the readings of the milliammeter, note whether an induction current occurred if:
* insert a magnet into the fixed coil,
* remove the magnet from the fixed coil,
* place the magnet inside the coil, leaving it motionless.
3. Find out how the magnetic flux Ф, penetrating the coil, changed in each case. Make a conclusion about the condition under which the inductive current appeared in the coil.
II. Study of the direction of the induction current.
1. The direction of the current in the coil can be judged by the direction in which the milliammeter needle deviates from zero division.
Check whether the direction of the induction current will be the same if:
* insert into the coil and remove the magnet with the north pole;
* insert the magnet into the magnet coil with the north pole and the south pole.
2. Find out what changed in each case. Make a conclusion about what determines the direction of the induction current. III. The study of the magnitude of the induction current.
1. Move the magnet closer to the fixed coil slowly and with greater speed, noting how many divisions (N 1 , N 2 ) the arrow of the milliammeter deviates.
2. Bring the magnet closer to the coil with the north pole. Note how many divisions N 1 the needle of the milliammeter deviates.
Attach the north pole of the bar magnet to the north pole of the arcuate magnet. Find out how many divisions N 2, the arrow of the milliammeter deviates when two magnets approach simultaneously.
3. Find out how the magnetic flux changed in each case. Make a conclusion on what the magnitude of the induction current depends.
Answer the questions:
1. First quickly, then slowly push the magnet into the coil of copper wire. Is it the same electric charge at the same time is transferred through the section of the wire of the coil?
2. Will there be an induction current in the rubber ring when a magnet is introduced into it?
Physics teacher GBOU secondary school No. 58 of the city of Sevastopol Safronenko N.I.
Lesson topic: Faraday's experiments. Electromagnetic induction.
Laboratory work"Investigation of the phenomenon of electromagnetic induction"
Lesson Objectives : Know/understand: definition of the phenomenon of electromagnetic induction. Be able to describe and explain electromagnetic induction,be able to observe natural phenomena, use simple measuring instruments to study physical phenomena.
- developing: develop logical thinking, cognitive interest, observation.
- educational: Build confidence in the possibility of knowing nature,necessityreasonable use of scientific achievements for further development human society respect for the creators of science and technology.
Equipment: Electromagnetic induction: galvanometer coil, magnet, core coil, current source, rheostat, AC core coil, solid and slotted ring, bulb coil. A film about M. Faraday.
Lesson type: combined lesson
Lesson method: partially exploratory, explanatory and illustrative
Homework:
§21(p.90-93), orally answer questions p.90, test 11 p.108
Laboratory work
Study of the phenomenon of electromagnetic induction
Goal of the work: to figure out
1) under what conditions does an induction current occur in a closed circuit (coil);
2) what determines the direction of the induction current;
3) what determines the strength of the induction current.
Equipment : milliammeter, coil, magnet
During the classes.
Connect the ends of the coil to the milliammeter terminals.
1. Find out what electricity(induction) in the coil occurs when changing magnetic field inside the coil. Changes in the magnetic field inside a coil can be induced by pushing a magnet into or out of the coil.
a) Insert the magnet with the south pole into the coil, and then remove it.
b) Insert the magnet with the north pole into the coil, and then remove it.
When the magnet moved, did a current (inductive) appear in the coil? (When changing the magnetic field, did an induction current appear inside the coil?)
2. Find out what the direction of the induction current depends on the direction of movement of the magnet relative to the coil (the magnet is inserted or removed) and on which pole the magnet is inserted or removed.
a) Insert the magnet with the south pole into the coil, and then remove it. Observe what happens to the milliammeter needle in both cases.
b) Insert the magnet with the north pole into the coil, and then remove it. Observe what happens to the milliammeter needle in both cases. Draw the directions of deflection of the milliammeter needle:
magnet poles
To coil
From the reel
South Pole
North Pole
3. Find out what the strength of the induction current depends on the speed of the magnet (the rate of change of the magnetic field in the coil).
Slowly insert the magnet into the coil. Observe the milliammeter readings.
Quickly insert the magnet into the coil. Observe the milliammeter readings.
Conclusion.
During the classes
Road to knowledge? She is easy to understand. The answer is simple: “You are wrong and wrong again, but less, less each time. I express the hope that today's lesson will be one less on this path of knowledge. Our lesson is devoted to the phenomenon of electromagnetic induction, which was discovered by English physicist Michael Faraday August 29, 1831. A rare case when the date of a new remarkable discovery is known so precisely!
The phenomenon of electromagnetic induction is the phenomenon of the occurrence of an electric current in a closed conductor (coil) when an external magnetic field changes inside the coil. The current is called inductive. Induction - pointing, receiving.
The purpose of the lesson: study the phenomenon of electromagnetic induction, i.e. under what conditions does an induction current occur in a closed circuit (coil), find out what determines the direction and magnitude of the induction current.
Simultaneously with the study of the material, you will perform laboratory work.
At the beginning of the 19th century (1820), after the experiments of the Danish scientist Oersted, it became clear that an electric current creates a magnetic field around itself. Let's revisit this experience. (Student tells Oersted's experience ). After that, the question arose of whether it is possible to obtain a current using a magnetic field, i.e. perform the reverse action. In the first half of the 19th century, scientists turned to just such experiments: they began to look for the possibility of creating an electric current due to a magnetic field. M. Faraday wrote in his diary: "Turn magnetism into electricity." And he went to his goal for almost ten years. Handled the task brilliantly. As a reminder of what he should be thinking about all the time, he carried a magnet in his pocket. With this lesson, we will pay tribute to the great scientist.
Consider Michael Faraday. Who is he? (The student talks about M. Faraday ).
The son of a blacksmith, a newspaper peddler, a bookbinder, a self-taught person who independently studied physics and chemistry from books, a laboratory assistant to the outstanding chemist Devi and finally a scientist, did a great job, showed ingenuity, perseverance, perseverance until he received an electric current using a magnetic field.
Let's take a trip to those distant times and reproduce Faraday's experiments. Faraday is considered the greatest experimenter in the history of physics.
N S
1) 2)
SN
The magnet was inserted into the coil. When the magnet moved, a current (induction) was recorded in the coil. The first scheme was quite simple. Firstly, M. Faraday used a coil with a large number turns. The coil was connected to a milliammeter instrument. It must be said that in those distant times there were not enough good instruments for measuring electric current. Therefore, they used an unusual technical solution: they took a magnetic needle, placed a conductor next to it, through which current flowed, and the current flow was judged by the deviation of the magnetic needle. We will judge the current by the readings of a milliammeter.
Students reproduce the experience, perform step 1 in the laboratory work. We noticed that the milliammeter needle deviates from its zero value, i.e. shows that a current appeared in the circuit when the magnet moves. As soon as the magnet stops, the arrow returns to the zero position, i.e. there is no electric current in the circuit. Current appears when the magnetic field inside the coil changes.
We came to what we talked about at the beginning of the lesson: we got an electric current using a changing magnetic field. This is the first merit of M. Faraday.
The second merit of M. Faraday - he established what the direction of the induction current depends on. We will install it too.Students complete item 2 in the laboratory work. Let us turn to paragraph 3 of the laboratory work. Let us find out that the strength of the induction current depends on the speed of the magnet (the rate of change of the magnetic field in the coil).
What conclusions did M. Faraday draw?
An electric current appears in a closed circuit when the magnetic field changes (if the magnetic field exists, but does not change, then there is no current).
The direction of the induction current depends on the direction of movement of the magnet and its poles.
The strength of the inductive current is proportional to the rate of change of the magnetic field.
The second experiment of M. Faraday:
I took two coils on a common core. One connected to a milliammeter, and the second with a key to a current source. As soon as the circuit was closed, the milliammeter showed the induction current. Opened, too, showed current. While the circuit is closed, i.e. there is current in the circuit, the milliammeter did not show the current. The magnetic field exists but does not change.
Consider modern version M. Faraday's experiments. We bring in and take out an electromagnet, a core into a coil connected to a galvanometer, turn the current on and off, change the current strength with the help of a rheostat. A coil with a light bulb is put on the core of the coil through which alternating current flows.
Found out conditions occurrence in a closed circuit (coil) of induction current. And what iscause its occurrence? Recall the conditions for the existence of an electric current. These are: charged particles and electric field. The fact is that a changing magnetic field generates an electric field (vortex) in space, which acts on free electrons in the coil and sets them in a directed motion, thus creating an induction current.
The magnetic field changes, the number of magnetic field lines through a closed loop changes. If you rotate the frame in a magnetic field, then an induction current will appear in it.Show generator model.
The discovery of the phenomenon of electromagnetic induction was of great importance for the development of technology, for the creation of generators, with the help of which electrical energy is generated, which stand on energy industrial enterprises(power stations).A film about M. Faraday "From electricity to electric generators" is shown from 12.02 minutes.
Transformers work on the phenomenon of electromagnetic induction, with the help of which they transmit electricity without loss.A power line is shown.
The phenomenon of electromagnetic induction is used in the operation of a flaw detector, with the help of which steel beams and rails are examined (heterogeneities in the beam distort the magnetic field and an induction current appears in the flaw detector coil).
I would like to recall the words of Helmholtz: "As long as people enjoy the benefits of electricity, they will remember the name of Faraday."
“May those be holy who, in creative fervor, exploring the whole world, discovered laws in it.”
I think that on our road of knowledge there are even fewer mistakes.
What have you learned? (That the current can be obtained using a changing magnetic field. We found out what the direction and magnitude of the induction current depend on).
What have you learned? (Get an induction current using a changing magnetic field).
Questions:
A magnet is inserted into the metal ring during the first two seconds, during the next two seconds it is motionless inside the ring, during the next two seconds it is removed. How long does it take for the current to flow through the coil? (From 1-2s; 5-6s).
A ring with a slot and without is put on the magnet. What is the induced current? (In a closed circle)
On the core of the coil, which is connected to an alternating current source, there is a ring. Turn on the current and the ring bounces. Why?
Board layout:
"Turn magnetism into electricity"
M. Faraday
Portrait of M. Faraday
Drawings of M. Faraday's experiments.
Electromagnetic induction is the phenomenon of the occurrence of an electric current in a closed conductor (coil) when an external magnetic field changes inside the coil.
This current is called inductive.
You already know that there is always a magnetic field around an electric current. Electric current and magnetic field are inseparable from each other.
But if an electric current is said to "create" a magnetic field, isn't there the opposite? Is it possible to "create" an electric current with the help of a magnetic field?
Such a task in early XIX V. tried to solve many scientists. The English scientist Michael Faraday also put it in front of him. “Turn magnetism into electricity” - this is how Faraday wrote this problem in his diary in 1822. It took the scientist almost 10 years of hard work to solve it.
Michael Faraday (1791-1867)
English physicist. He discovered the phenomenon of electromagnetic induction, extra currents during closing and opening
To understand how Faraday was able to "turn magnetism into electricity", let's perform some of Faraday's experiments using modern instruments.
Figure 119, a shows that if a magnet is inserted into a coil closed to a galvanometer, then the galvanometer needle deviates, indicating the appearance of an induction (induced) current in the coil circuit. The induction current in a conductor is the same ordered movement of electrons as the current received from a galvanic cell or battery. The name "induction" indicates only the reason for its occurrence.
Rice. 119. The occurrence of an inductive current when a magnet and a coil move relative to each other
When the magnet is removed from the coil, the deviation of the galvanometer needle is again observed, but in opposite side, which indicates the occurrence of current in the opposite direction in the coil.
As soon as the movement of the magnet relative to the coil stops, the current stops. Therefore, the current in the coil circuit exists only during the movement of the magnet relative to the coil.
Experience can be changed. We will put a coil on a fixed magnet and remove it (Fig. 119, b). And again, you can find that during the movement of the coil relative to the magnet, a current appears in the circuit again.
Figure 120 shows coil A included in the current source circuit. This coil is inserted into another coil C connected to a galvanometer. When the circuit of coil A is closed and opened, an induction current occurs in coil C.
Rice. 120. Occurrence of inductive current when closing and opening an electrical circuit
You can cause the appearance of an induction current in coil C and by changing the current strength in coil A or by moving these coils relative to each other.
Let's do one more experiment. Let us place a flat contour of a conductor in a magnetic field, the ends of which we will connect to a galvanometer (Fig. 121, a). When the circuit is rotated, the galvanometer notes the appearance of an induction current in it. The current will also appear if a magnet is rotated near or inside the circuit (Fig. 121, b).
Rice. 121. When the circuit rotates in a magnetic field (magnet relative to the circuit), a change in the magnetic flux leads to the appearance of an induction current
In all the experiments considered, the induction current arose when the magnetic flux penetrating the area covered by the conductor changed.
In the cases depicted in figures 119 and 120, the magnetic flux changed due to a change in the magnetic field induction. Indeed, when the magnet and the coil moved relative to each other (see Fig. 119), the coil fell into the field with a greater or lesser magnetic induction (since the field of the magnet is non-uniform). When closing and opening the circuit of coil A (see Fig. 120), the induction of the magnetic field created by this coil changed due to a change in the current strength in it.
When the wire circuit rotated in a magnetic field (see Fig. 121, a) or the magnet relative to the circuit (see Fig. 121, b "), the magnetic flux changed due to a change in the orientation of this circuit with respect to the lines of magnetic induction.
Thus,
- with any change in the magnetic flux penetrating the area bounded by a closed conductor, an electric current arises in this conductor, which exists during the entire process of changing the magnetic flux
This is the phenomenon of electromagnetic induction.
The discovery of electromagnetic induction is one of the most remarkable scientific achievements first half of XIX V. It caused the emergence and rapid development of electrical and radio engineering.
Based on the phenomenon of electromagnetic induction, powerful generators were created electrical energy, in the development of which scientists and technicians from different countries took part. Among them were our compatriots: Emil Khristianovich Lenz, Boris Semyonovich Jacobi, Mikhail Iosifovich Dolivo-Dobrovolsky and others who contributed huge contribution in the development of electrical engineering.
Questions
- What was the purpose of the experiments depicted in Figures 119-121? How were they carried out?
- Under what condition in the experiments (see Fig. 119, 120) did an induction current arise in a coil closed to a galvanometer?
- What is the phenomenon of electromagnetic induction?
- What is the importance of discovering the phenomenon of electromagnetic induction?
Exercise 36
- How to create a short-term induction current in coil K 2 shown in Figure 118?
- The wire ring is placed in a uniform magnetic field (Fig. 122). The arrows shown next to the ring show that in cases a and b the ring moves in a straight line along the lines of magnetic field induction, and in cases c, d and e it rotates around the axis OO. "In which of these cases can an induction current occur in the ring ?
Lesson Plan
Lesson topic: Laboratory work: "Studying the phenomenon of electromagnetic induction"
Type of occupation - mixed.
Lesson type combined.
Learning objectives of the lesson: to study the phenomenon of electromagnetic induction
Lesson objectives:
Educational:study the phenomenon of electromagnetic induction
Developing. To develop the ability to observe, form an idea of the process of scientific knowledge.
Educational. Develop cognitive interest in the subject, develop the ability to listen and be heard.
Planned educational outcomes: to contribute to strengthening the practical orientation in teaching physics, the formation of skills to apply the acquired knowledge in various situations.
Personality: with contribute to the emotional perception of physical objects, the ability to listen, clearly and accurately express their thoughts, develop initiative and activity in solving physical problems, form the ability to work in groups.
Metasubject: pdevelop the ability to understand and use visual aids (drawings, models, diagrams). Development of an understanding of the essence of algorithmic prescriptions and the ability to act in accordance with the proposed algorithm.
subject: about know the physical language, the ability to recognize parallel and serial connections, the ability to navigate in an electrical circuit, to assemble circuits. Ability to generalize and draw conclusions.
Lesson progress:
1. Organization of the beginning of the lesson (marking absentees, checking students' readiness for the lesson, answering students' questions on homework) - 2-5 min.
The teacher tells the students the topic of the lesson, formulates the objectives of the lesson and introduces the students to the lesson plan. Students write the topic of the lesson in their notebooks. The teacher creates conditions for the motivation of learning activities.
Mastering new material:
Theory. The phenomenon of electromagnetic inductionconsists in the occurrence of an electric current in a conducting circuit, which either rests in an alternating 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 magnetic field at each point in space is characterized by the magnetic induction vector B. Let a closed conductor (circuit) be placed in a uniform magnetic field (see Fig. 1.)
Picture 1.
Normal to the plane of the conductor makes an anglewith the direction of the magnetic induction vector.
magnetic fluxФ through a surface with an area S is called a value equal to the product of the modulus of the magnetic induction vector B and the area S and the cosine of the anglebetween vectors And .
Ф=В S cos α (1)
The direction of the inductive current that occurs in a closed circuit when the magnetic flux through it changes is determined by Lenz's rule: the inductive current arising in a closed circuit counteracts with its magnetic field the change in the magnetic flux by which it is caused.
Apply Lenz's rule as follows:
1. Set the direction of the lines of magnetic induction B of the external magnetic field.
2. Find out if the magnetic induction flux of this field increases through the surface bounded by the contour ( F 0), or decreases ( F 0).
3. Set the direction of the lines of magnetic induction B "magnetic field
inductive current Iusing the gimlet rule.
When the magnetic flux changes through the surface bounded by the contour, external forces appear in the latter, the action of which is characterized by the EMF, called EMF of induction.
According to the law of electromagnetic induction, the EMF of induction in a closed loop is equal in absolute value to the rate of change of the magnetic flux through the surface bounded by the loop:
Devices and equipment:galvanometer, power supply, core coils, arched magnet, key, connecting wires, rheostat.
Work order:
1. Obtaining an induction current. For this you need:
1.1. Using figure 1.1., assemble a circuit consisting of 2 coils, one of which is connected to the source direct current through a rheostat and a key, and the second, located above the first, is connected to a sensitive galvanometer. (see fig. 1.1.)
Figure 1.1.
1.2. Close and open the circuit.
1.3. Make sure that the induction current occurs in one of the coils at the moment of closing the electrical circuit of the coil, which is stationary relative to the first, while observing the direction of deviation of the galvanometer needle.
1.4. Set in motion a coil connected to a galvanometer relative to a coil connected to a direct current source.
1.5. Make sure that the galvanometer detects the occurrence of an electric current in the second coil with any movement of it, while the direction of the arrow of the galvanometer will change.
1.6. Perform an experiment with a coil connected to a galvanometer (see Fig. 1.2.)
Figure 1.2.
1.7. Make sure that the induction current occurs when the permanent magnet moves relative to the coil.
1.8. Make a conclusion about the cause of the induction current in the experiments performed.
2. Checking the fulfillment of the Lenz rule.
2.1. Repeat the experiment from paragraph 1.6. (Fig. 1.2.)
2.2. For each of the 4 cases of this experiment, draw diagrams (4 diagrams).
Figure 2.3.
2.3. Check the fulfillment of the Lenz rule in each case and fill in Table 2.1 according to these data.
Table 2.1.
N experience | Method for obtaining induction current | ||||
Insertion into the coil north pole magnet | increases |
||||
Removing the magnet's north pole from the coil | decreasing |
||||
Insertion into the coil south pole magnet | increases |
||||
Removing the South Pole of the Magnet from the Coil | decreasing |
3. Make a conclusion about the laboratory work done.
4. Answer security questions.
Control questions:
1. How should a closed circuit move in a uniform magnetic field, translationally or rotationally, so that an inductive current arises in it?
2. Explain why the inductive current in the circuit has such a direction that its magnetic field prevents a change in the magnetic flux of its cause?
3. Why is there a "-" sign in the law of electromagnetic induction?
4. A magnetized steel bar falls through a magnetized ring along its axis, the axis of which is perpendicular to the plane of the ring. How will the current in the ring change?
Admission to laboratory work 11
1. What is the name of the power characteristic of the magnetic field? Its graphic meaning.
2. How is the modulus of the magnetic induction vector determined?
3. Give the definition of the unit of measurement of the magnetic field induction.
4. How is the direction of the magnetic induction vector determined?
5. Formulate the gimlet rule.
6. Write down the formula for calculating the magnetic flux. What is its graphic meaning?
7. Define the unit of measure for magnetic flux.
8. What is the phenomenon of electromagnetic induction?
9. What is the reason for the separation of charges in a conductor moving in a magnetic field?
10. What is the reason for the separation of charges in a stationary conductor in an alternating magnetic field?
11. Formulate the law of electromagnetic induction. Write down the formula.
12. Formulate Lenz's rule.
13. Explain Lenz's rule based on the law of conservation of energy.
Michael Faraday was the first to study the phenomenon of electromagnetic induction. More precisely, he established and investigated this phenomenon in search of ways to turn magnetism into electricity.
It took him ten years to solve such a problem, but now we use the fruits of his labor everywhere, and we can’t imagine modern life without the use of electromagnetic induction. In the 8th grade, we already considered this topic, in the 9th grade this phenomenon is considered in more detail, but the derivation of formulas refers to the 10th grade course. You can follow this link to get acquainted with all aspects of this issue.
The phenomenon of electromagnetic induction: consider the experience
We will consider what constitutes the phenomenon of electromagnetic induction. You can conduct an experiment for which you need a galvanometer, permanent magnet and coil. By connecting the galvanometer to the coil, we push a permanent magnet inside the coil. In this case, the galvanometer will show the change in current in the circuit.
Since we do not have any current source in the circuit, it is logical to assume that the current arises due to the appearance of a magnetic field inside the coil. When we pull the magnet back out of the coil, we will see that the readings of the galvanometer will change again, but its needle will deviate in the opposite direction. We will again receive a current, but already directed in the other direction.
Now we will do a similar experiment with the same elements, only at the same time we will fix the magnet motionless, and we will now put the coil itself on and off the magnet, connected to the galvanometer. We will get the same results. The pointer of the galvanometer will show us the appearance of current in the circuit. In this case, when the magnet is stationary, there is no current in the circuit, the arrow stands at zero.
It is possible to carry out a modified version of the same experiment, only to replace the permanent magnet with an electric one, which can be turned on and off. We will get results similar to the first experience when the magnet moves inside the coil. But, in addition, when turning off and turning off a stationary electromagnet, it will cause a short-term appearance of current in the coil circuit.
The coil can be replaced by a conducting circuit and experiments can be done on moving and rotating the circuit itself in a constant magnetic field, or a magnet inside a fixed circuit. The results will be the same appearance of current in the circuit when the magnet or circuit moves.
A change in the magnetic field causes a current to appear
From all this it follows that a change in the magnetic field causes the appearance of an electric current in the conductor. This current is no different from the current that we can get from batteries, for example. But to indicate the cause of its occurrence, such a current was called induction.
In all cases, we changed the magnetic field, or rather, the magnetic flux through the conductor, as a result of which a current arose. Thus, the following definition can be derived:
With any change in the magnetic flux penetrating the circuit of a closed conductor, an electric current arises in this conductor, which exists during the entire process of changing the magnetic flux.
