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Laboratory work № 9
Phenomenon study electromagnetic induction
Objective: to study the conditions for the occurrence of induction current, EMF induction.
Equipment: coil, two bar magnets, milliammeter.
Theory
The mutual connection of electric and magnetic fields was established by the outstanding English physicist M. Faraday in 1831. He discovered the phenomenon electromagnetic induction.
Numerous experiments by Faraday show that with the help of magnetic field you can get an electric current in the conductor.
The phenomenon of electromagnetic inductionlies in the occurrence electric current in a closed loop when changing magnetic flux penetrating the contour.
The current that occurs during the phenomenon of electromagnetic induction is called induction.
AT electrical circuit(Figure 1) an induction current occurs if there is movement of the magnet relative to the coil, or vice versa. The direction of the induction current depends both on the direction of movement of the magnet and on the location of its poles. There is no induction current if there is no relative movement of the coil and magnet.
Picture 1.
Strictly speaking, when the circuit moves in a magnetic field, not a certain current is generated, but a certain e. d.s.
Figure 2.
Faraday experimentally found that when the magnetic flux changes in the conducting circuit, an EMF of induction occurs E ind, equal to speed changes in magnetic flux through a surface bounded by a contour, taken with a minus sign:
This formula expresses Faraday's law:e. d.s. induction is equal to the rate of change of the magnetic flux through the surface bounded by the contour.
The minus sign in the formula reflects Lenz's rule.
In 1833, Lenz experimentally proved a statement called Lenz's rule: the induction current excited in a closed circuit when the magnetic flux changes is always directed so that the magnetic field it creates prevents a change in the magnetic flux that causes the induction current.
With increasing magnetic fluxФ>0, and ε ind< 0, т.е. э. д. с. индукции вызывает ток такого направления, при котором его магнитное поле уменьшает магнитный поток через контур.
With decreasing magnetic flux F<0, а ε инд >0, i.e. the magnetic field of the inductive current increases the decreasing magnetic flux through the circuit.
Lenz's rule has a deep physical meaning – it expresses the law of conservation of energy: if the magnetic field through the circuit increases, then the current in the circuit is directed so that its magnetic field is directed against the external one, and if the external magnetic field through the circuit decreases, then the current is directed so that its magnetic field supports this decreasing magnetic field.
The induction emf depends on various reasons. If a strong magnet is pushed into the coil once, and a weak one the other time, then the readings of the device in the first case will be higher. They will also be higher when the magnet is moving fast. In each of the experiments carried out in this work, the direction of the induction current is determined by the Lenz rule. The procedure for determining the direction of the induction current is shown in Figure 2.
In the figure, the lines of force of the magnetic field of the permanent magnet and the lines of the magnetic field of the induction current are indicated in blue. The magnetic field lines are always directed from N to S - from the north pole to the south pole of the magnet.
According to Lenz's rule, the inductive electric current in the conductor, which occurs when the magnetic flux changes, is directed in such a way that its magnetic field counteracts the change in the magnetic flux. Therefore, in the coil direction lines of force magnetic field is opposite to the lines of force of a permanent magnet, because the magnet moves towards the coil. We find the direction of the current according to the rule of the gimlet: if the gimlet (with right-hand thread) is screwed in so that it forward movement coincided with the direction of the induction lines in the coil, then the direction of rotation of the gimlet handle coincides with the direction of the induction current.
Therefore, the current through the milliammeter flows from left to right, as shown in Figure 1 by the red arrow. In the case when the magnet moves away from the coil, the magnetic field lines of the inductive current will coincide in direction with the lines of force of the permanent magnet, and the current will flow from right to left.
Working process.
Prepare a table for the report and fill it in as the experiments are carried out.
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Actions with a magnet and a coil |
Indications milli-ammeter, |
Deflection directions of the milliamp meter needle (right, left, or no bow) |
Direction of induction current (according to Lenz's rule) |
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Quickly insert the magnet into the coil with the north pole |
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Leave the magnet in the coil stationary after experience 1 |
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Quickly pull the magnet out of the coil |
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Move the coil quickly to the north pole of the magnet |
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Leave the coil motionless after experiment 4 |
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Quickly pull the coil away from the north pole of the magnet |
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Slowly insert the north pole magnet into the coil |
Objective: experimental study of the phenomenon of magnetic induction verification of Lenz's rule.
Theoretical part:
The phenomenon of electromagnetic induction consists in the occurrence of an electric current in a conducting circuit, which either rests in a magnetic field that changes in time, or moves in a constant magnetic field in such a way that the number of magnetic induction lines penetrating the circuit changes. In 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?
test 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).
Working process
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, 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 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 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 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.
test 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 or in the opposite direction. With a sinusoidal current, the nature of this movement coincides with harmonic vibrations. 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
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, 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.
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
§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
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 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:
Got two coils 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 had great value for the development of technology, for the creation of generators, with the help of which electrical energy is generated, which are installed at 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.
