The phenomenon of electromagnetic induction. Laboratory work in physics: "Studying the phenomenon of electromagnetic induction" List of additional literature
In this lesson, we will conduct laboratory work No. 4 "Studying the phenomenon of electromagnetic induction." The purpose of this lesson will be to study the phenomenon of electromagnetic induction. Using the necessary equipment, we will conduct laboratory work, at the end of which we will learn how to properly study and determine this phenomenon.
The goal is to study phenomena of electromagnetic induction.
Equipment:
1. Milliammeter.
2. Magnet.
3. Coil-coil.
4. Current source.
5. Rheostat.
6. Key.
7. Coil from an electromagnet.
8. Connecting wires.
Rice. 1. Experimental equipment
Let's start the lab by collecting the setup. To assemble the circuit that we will use in the lab, we will attach a coil to a milliammeter and use a magnet that we will move closer or further away from the coil. At the same time, we must remember what will happen when the induction current appears.
Rice. 2. Experiment 1
Think about how to explain the phenomenon we are observing. How does the magnetic flux affect what we see, in particular the origin of the electric current. To do this, look at the auxiliary figure.
Rice. 3. Magnetic field lines of a permanent bar magnet
Please note that the lines of magnetic induction come out of the north pole, enter the south pole. At the same time, the number of these lines, their density is different in different parts of the magnet. Note that the direction of the magnetic field also changes from point to point. Therefore, we can say that a change in the magnetic flux leads to the fact that an electric current arises in a closed conductor, but only when the magnet moves, therefore, the magnetic flux penetrating the area limited by the turns of this coil changes.
The next stage of our study of electromagnetic induction is connected with the definition direction of induction current. We can judge the direction of the induction current by the direction in which the arrow of the milliammeter deviates. Let's use an arcuate magnet and we will see that when the magnet approaches, the arrow will deviate in one direction. If now the magnet is moved in the other direction, the arrow will deviate in the other direction. As a result of the experiment, we can say that the direction of the induction current also depends on the direction of movement of the magnet. We also note that the direction of the induction current also depends on the pole of the magnet.
Please note that the magnitude of the induction current depends on the speed of movement of the magnet, and at the same time on the rate of change of the magnetic flux.
The second part of our laboratory work will be connected with another experiment. Let's look at the scheme of this experiment and discuss what we will do now.
Rice. 4. Experiment 2
In the second circuit, in principle, nothing has changed regarding the measurement of the inductive current. The same milliammeter attached to the coil. Everything remains as it was in the first case. But now we will get a change in the magnetic flux not due to the movement of a permanent magnet, but due to a change in the current strength in the second coil.
In the first part, we will investigate the presence induction current when closing and opening the circuit. So, the first part of the experiment: we close the key. Pay attention, the current increases in the circuit, the arrow deviated to one side, but pay attention, now the key is closed, and the milliammeter does not show electric current. The fact is that there is no change in the magnetic flux, we have already talked about this. If the key is now opened, the milliammeter will show that the direction of the current has changed.
In the second experiment, we will see how induction current when the electric current in the second circuit changes.
The next part of the experiment will be to trace how the induction current will change if the current in the circuit is changed due to the rheostat. You know that if we change the electrical resistance in a circuit, then, following Ohm's law, our electric current will also change. As the electric current changes, the magnetic field will change. At the moment of moving the sliding contact of the rheostat, the magnetic field changes, which leads to the appearance of an induction current.
To conclude the lab, we should look at how an inductive electric current is created in an electric current generator.
Rice. 5. Electric current generator
Its main part is a magnet, and inside these magnets there is a coil with a certain number of wound turns. If we now rotate the wheel of this generator, an induction electric current will be induced in the coil winding. From the experiment it can be seen that an increase in the number of revolutions leads to the fact that the bulb starts to burn brighter.
List of additional literature:
Aksenovich L. A. Physics in high school: Theory. Tasks. Tests: Proc. allowance for institutions providing general. environments, education / L.A. Aksenovich, N.N. Rakina, K. S. Farino; Ed. K. S. Farino. - Mn.: Adukatsy i vykhavanne, 2004. - C. 347-348. Myakishev G.Ya. Physics: Electrodynamics. 10-11 grades. Textbook for in-depth study of physics / G.Ya. Myakishev, A.3. Sinyakov, V.A. Slobodskov. - M.: Bustard, 2005. - 476 p. Purysheva N.S. Physics. Grade 9 Textbook. / Purysheva N.S., Vazheevskaya N.E., Charugin V.M. 2nd ed., stereotype. - M.: Bustard, 2007.
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, make 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 and moves away from it.
4. 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 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 
Control questions
1.What is electric capacity?
2. Define the following concepts: alternating current, amplitude, frequency, cyclic frequency, period, phase of oscillation
Lab 11
Studying the phenomenon of electromagnetic induction
Objective: study the phenomenon of electromagnetic induction .
Equipment: milliammeter; coil-coil; arched magnet; source of power; a coil with an iron core from a collapsible electromagnet; rheostat; key; connecting wires; electric current generator model (one).
Progress
1. Connect the coil-coil to the clamps of the milliammeter.
2. Observing 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.). Write down whether an induction current occurred in the coil during the movement of the magnet relative to the coil; during his stop.
3. 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, make 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 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 and moves away from it.
7. Approach the pole of the magnet to the coil at such a speed that the needle of the milliammeter 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, did a current appear larger in magnitude 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 penetrating this coil.
8. Assemble the installation for the experiment according to the drawing.
9. Check whether there is an induction current in coil 1 in the following cases:
a. when closing and opening the circuit, which includes the coil 2;
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 the coil change? Why is he changing?
11. Observe the occurrence of electric current in the generator model (Fig.). Explain why an induction current occurs in a frame rotating in a magnetic field.
Control questions
1. Formulate the law of electromagnetic induction.
2. By whom and when was the law of electromagnetic induction formulated?
Lab 12
Measuring coil inductance
Objective: The study of the basic laws of electrical circuits of alternating current and familiarity with the simplest ways to measure inductance and capacitance.
Brief theory
Under the influence of a variable electromotive force (EMF) in an electrical circuit, an alternating current arises in it.
An alternating current is a current that changes in direction and magnitude. In this paper, only such an alternating current is considered, the value of which changes periodically according to a sinusoidal law.
Consideration of the sinusoidal current is due to the fact that all large power plants produce alternating currents that are very close to sinusoidal currents.
Alternating current in metals is the movement of free electrons in one direction, then in the opposite direction. With a sinusoidal current, the nature of this movement coincides with harmonic oscillations. Thus, a sinusoidal alternating current has a period T- the time of one complete oscillation and the frequency v number of complete oscillations per unit of time. There is a relationship between these quantities
The AC circuit, unlike the DC circuit, allows the inclusion of a capacitor.
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called full resistance or impedance chains. Therefore, expression (8) is called Ohm's law for alternating current.
In this work, active resistance R coil is determined using Ohm's law for a section of a DC circuit.
Let's consider two special cases.
1. There is no capacitor in the circuit. This means that the capacitor is turned off and instead the circuit is closed by a conductor, the potential drop on which is practically zero, that is, the value U in equation (2) is zero..gif" alt="(!LANG:http://web-local.rudn.ru/web-local/uem/ido/8/Image474.gif" width="54" height="18">.!}
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2. There is no coil in the circuit: hence .
For from formulas (6), (7), and (14), respectively, we have
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 peddler of newspapers, a book binder, 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 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.
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.
