Laboratory work in physics: "Studying the phenomenon of electromagnetic induction." The phenomenon of electromagnetic induction The study of the phenomenon of electromagnetic induction

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,needreasonable use of the achievements of science for the further development of 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

Objective: 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 an electric current (inductive) in the coil occurs when the magnetic field inside the coil changes. 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 the English physicist Michael Faraday on 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 for the outstanding chemist Devi and finally a scientist, did a great job, showed ingenuity, perseverance, perseverance until he received an electric current with the help of 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 of turns in his experiments. 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 the modern version of 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 are used in energy industrial enterprises (power plants).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.

The purpose of the work: To study the phenomenon of electromagnetic induction.
Equipment: milliammeter, coil coil, arcuate magnet, power source, iron core coil from a collapsible electromagnet, rheostat, key, connecting wires, electric current generator model (one per class).
Instructions for work:
1. Connect the coil-coil to the clamps of the milliammeter.
2. Watching the readings of the milliammeter, bring one of the poles of the magnet to the coil, then stop the magnet for a few seconds, and then again bring it closer to the coil, sliding it into it (Fig. 196). Write down whether an induction current occurred in the coil during the movement of the magnet relative to the coil; during his stop.

Write down whether the magnetic flux Ф, penetrating the coil, changed during the movement of the magnet; during his stop.
4. Based on your answers to the previous question, draw and write down the conclusion under what condition an induction current occurred in the coil.
5. Why did the magnetic flux penetrating this coil change when the magnet approached the coil? (To answer this question, remember, firstly, on what quantities does the magnetic flux Ф depend and, secondly, is the same
whether the modulus of the induction vector B of the magnetic field of a permanent magnet near this magnet and away from it.)
6. 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 in the coil will be the same or different when the same pole of the magnet approaches it and moves away from it.

4. Approach the magnet pole to the coil at such a speed that the milliammeter needle deviates by no more than half the limit value of its scale.
Repeat the same experiment, but at a higher speed of the magnet than in the first case.
With a greater or lesser speed of movement of the magnet relative to the coil, did the magnetic flux Ф penetrating this coil change faster?
With a rapid or slow change in the magnetic flux through the coil, was the current strength in it greater?
Based on your answer to the last question, make and write down the conclusion about how the modulus of the strength of the induction current that occurs in the coil depends on the rate of change of the magnetic flux Ф penetrating this coil.
5. Assemble the setup for the experiment according to Figure 197.
6. Check whether there is an induction current in coil 1 in the following cases:
a) when closing and opening the circuit in which coil 2 is included;
b) when flowing through the coil 2 direct current;
c) with an increase and decrease in the strength of the current flowing through the coil 2, by moving the rheostat slider to the appropriate side.
10. In which of the cases listed in paragraph 9 does the magnetic flux penetrating coil 1 change? Why is he changing?
11. Observe the occurrence of electric current in the generator model (Fig. 198). Explain why an induction current occurs in a frame rotating in a magnetic field.
Rice. 196

LABORATORY WORK "STUDYING THE PHENOMENON OF ELECTROMAGNETIC INDUCTION" The purpose of lesson 6 is to study the phenomenon of electromagnetic induction. Equipment: milliammeter, coil-coil, power source, coil with an iron core from a collapsible electromagnet, rheostat, key, connecting wires, magnet. Workflow 1. Connect the coil-coil to the clamps of the milliammeter. 2. Watching the readings of the milliammeter, bring one of the poles of the magnet to the coil, then stop the magnet for a few seconds, and then again bring it closer to the coil, moving into it. 3. Write down whether an induction current appeared in the coil during the movement of the magnet relative to the coil? During his stop? 4. Write down whether the magnetic flux Ф, penetrating the coil, changed during the movement of the magnet? During his stop? 5. Based on your answers to the previous question, draw and write down the condition under which the induction current occurred in the coil. 6. Why did the magnetic flux penetrating this coil change when the magnet approached the coil? (to answer this question, remember, firstly, on what quantities does the magnetic flux Ф depend and, secondly, is the modulus of the magnetic induction vector B of the magnetic field of a permanent magnet near this magnet and away from it.) 7. On 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 in the coil will be the same or different when the same pole of the magnet approaches and moves away from it. 8. Bring the magnet pole closer to the coil at such a speed that the milliammeter needle deviates by no more than half the limit value of its scale. Repeat the same experiment, but at a higher speed of the magnet than in the first case. With a greater or lesser speed of movement of the magnet relative to the coil, did the magnetic flux Ф penetrating this coil change faster? With a fast or slow change in the magnetic flux through the coil, did a larger current appear in it? Based on your answer to the last question, make and write down the conclusion about how the modulus of the strength of the induction current that occurs in the coil depends on the rate of change of the magnetic flux Ф, about

150.000₽ prize fund 11 documents of honor Evidence of publication in the media

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 work everywhere, and we cannot 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, a permanent magnet and a 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.

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 at the beginning of the XIX century. 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 galvanometer arrow again deviates, but in the opposite direction, which indicates the occurrence of current in the coil in the opposite direction.

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.

In this way,

• 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 of the first half of the 19th century. It caused the emergence and rapid development of electrical and radio engineering.

Based on the phenomenon of electromagnetic induction, powerful generators of electrical energy were created, 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 made a great contribution to the development of electrical engineering.

Questions

1. What was the purpose of the experiments depicted in Figures 119-121? How were they carried out?
2. Under what condition in the experiments (see Fig. 119, 120) did an induction current arise in a coil closed to a galvanometer?
3. What is the phenomenon of electromagnetic induction?
4. What is the importance of discovering the phenomenon of electromagnetic induction?

Exercise 36

1. How to create a short-term induction current in coil K 2 shown in Figure 118?
2. 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 rectilinearly along the magnetic field induction lines, 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 ?