- " onclick="window.open(this.href,"win2","status=no,toolbar=no,scrollbars=yes,titlebar=no,menubar=no,resizable=yes,width=640,height=480,directories =no,location=no"); return false;" > Print
Laboratory work № 9
Study of the phenomenon of electromagnetic induction
Goal of the work: study the conditions for the occurrence of induced current, induced emf.
Equipment: coil, two strip magnets, milliammeter.
Theory
The mutual relationship between electric and magnetic fields was established by the outstanding English physicist M. Faraday in 1831. He discovered the phenomenon electromagnetic induction.
Numerous Faraday experiments show that using a magnetic field it is possible to produce an electric current in a conductor.
The phenomenon of electromagnetic inductionis the emergence electric current in a closed loop when changing magnetic flux piercing the contour.
The current arising from the phenomenon of electromagnetic induction is called induction.
In an electrical circuit (Figure 1), an induced 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 induced current if there is no relative movement of the coil and magnet.
Picture 1.
Strictly speaking, when a circuit moves in a magnetic field, it is not a certain current that is generated, but a certain e. d.s.
Figure 2.
Faraday experimentally established that when the magnetic flux changes in a conducting circuit, an induced emf E ind arises, equal to the rate of change of the magnetic flux through the surface bounded by the circuit, taken with a minus sign:
This formula expresses Faraday's law:e. d.s. induction is equal to the rate of change of 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 loop when the magnetic flux changes is always directed in such a way that the magnetic field it creates prevents the change in the magnetic flux causing the induced 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.
When the magnetic flux decreases F<0, а ε инд >0, i.e. the magnetic field of the induced current increases the decreasing magnetic flux through the circuit.
Lenz's rule has 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 in such a way 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 in such a way that its magnetic field supports this decreasing magnetic field.
The induced emf depends on various reasons. If you push a strong magnet into the coil once, and a weak one another time, then the readings of the device in the first case will be higher. They will also be higher when the magnet moves quickly. In each of the experiments carried out in this work, the direction of the induction current is determined by Lenz’s rule. The procedure for determining the direction of the induction current is shown in Figure 2.
In the figure, the magnetic field lines of a permanent magnet and the magnetic field lines of the induced 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 induced electric current in a conductor, arising 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 the direction of the magnetic field lines is opposite to the force lines of the permanent magnet, because the magnet moves towards the coil. We find the direction of the current using the gimlet rule: if a gimlet (with a right-hand thread) is screwed in so that its translational movement coincides 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 induced current will coincide in direction with the field lines of the permanent magnet, and the current will flow from right to left.
Progress.
Prepare a table for the report and fill it out as you conduct experiments.
|
Actions with magnet and coil |
Indications milli-ammeter, |
Directions of deflection of the milliampere meter needle (right, left or does not bow) |
Direction of induction current (according to Lenz's rule) |
|
|
Quickly insert the magnet into the coil with the north pole |
|
|||
|
Leave the magnet in the coil motionless after experience 1 |
|
|||
|
Quickly remove the magnet from the coil |
|
|||
|
Quickly bring the coil closer to the north pole of the magnet |
|
|||
|
Leave the coil motionless after experiment 4 |
|
|||
|
Quickly pull the coil away from the north pole of the magnet |
|
|||
|
Slowly insert the magnet into the coil with the north pole |
The student must:
be able to: handle and use physical instruments in laboratory work; investigate the phenomenon of electromagnetic induction - determine what determines the magnitude and direction of the induction current; use the necessary reference literature;
know: methods for measuring the power consumed by an electrical appliance; the dependence of the power consumed by the light bulb on the voltage at its terminals; investigate the dependence of conductor resistance on temperature.
Occupation availability
Equipment and tools: milliammeter, coil-coil, arc-shaped magnet, strip magnet, direct current source, two coils with cores, rheostat, key, long wire, connecting wires.
Handouts:
Brief theoretical materials on the topic of laboratory work
Induction current in a closed loop occurs when the magnetic flux changes through the area limited by the loop. Changing the magnetic flux through the circuit can be done in two ways: different ways:
1) a change in time of the magnetic field in which the stationary circuit is located when the magnet is pushed into the coil or when pulled out;
2) the movement of this circuit (or its parts) in a constant magnetic field (for example, when putting a coil on a magnet).
Instructions for performing laboratory work
Connect the coil-coil to the clamps of the milliammeter, and then put it on and off the north pole of the arc-shaped magnet at different speeds (see figure), and for each case note the maximum and minimum strength of the induced current and the direction of deflection of the arrow of the device.
Figure 9.1
1. Turn the magnet over and slowly push the south pole of the magnet into the coil and then pull it out. Repeat the experiment at higher speed. Pay attention to where the milliammeter needle deviated this time.
2. Place two magnets (strip and arc-shaped) with like poles and repeat the experiment with different speeds of movement of the magnets in the coil.
3. Connect a long wire, rolled into several turns, to the clamps of the milliammeter instead of the coil. As you slide the coils of wire on and off the pole of the arc-shaped magnet, note the maximum strength of the induced current. Compare it with the maximum strength of the induced current obtained in experiments with the same magnet and coil, and discover the dependence of the induced emf on the length (number of turns) of the conductor.
4. Analyze your observations and draw conclusions regarding the reasons on which the magnitude of the induction current and its direction depend.
5. Assemble the circuit shown in Figure 1. The coils with the cores inserted into them should be located close to one another and so that their axes coincide.
6. Carry out the following experiments:
a) set the rheostat slider to the position corresponding minimum resistance rheostat. Close the circuit with the key while observing the milliammeter needle;
b) open the circuit with the key. What changed?
c) set the rheostat slider to the middle position. Repeat the experiment;
d) set the rheostat slider to the position corresponding to the maximum resistance of the rheostat. Close and open the circuit with the key.
7. Analyze your observations and draw conclusions.
Laboratory work No. 10
DEVICE AND OPERATION OF THE TRANSFORMER
The student must:
be able to: determine the transformation ratio; use the necessary reference literature;
know: device and principle of operation of the transformer.
Occupation availability
Equipment and tools: source of adjustable alternating voltage, collapsible laboratory transformer, alternating current voltmeters (or avometer), key, connecting wires;
Handouts: data guidelines for performing laboratory work.
Michael Faraday was the first to study the phenomenon of electromagnetic induction in earnest. More precisely, he established and studied this phenomenon in search of ways to turn magnetism into electricity.
It took him ten years to solve this 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 the formulas relates 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 experience
We will look at what the phenomenon of electromagnetic induction is. You can conduct an experiment for which you will 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 galvanometer readings will change again, but its needle will deviate in the opposite direction. We will again receive a current, but this time directed in the other direction.
Now let's do a similar experiment with the same elements, only in this case we will fix the magnet motionless, and we will now put the coil itself connected to the galvanometer on and off the magnet. We will get the same results. The galvanometer needle will show us the appearance of current in the circuit. At the same time, when the magnet is stationary, there is no current in the circuit, the arrow is at zero.
You can conduct a modified version of the same experiment, only replace the permanent magnet with an electric one, which can be turned on and off. We will obtain results similar to the first experiment when the magnet moves inside the coil. But, in addition, when a stationary electromagnet is turned on and off, it will cause a short-term appearance of current in the coil circuit.
The coil can be replaced with 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 stationary circuit. The results will be the same as the 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 reason for its occurrence, such a current was called induction.
In all cases, our magnetic field changed, 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 throughout the entire process of changing the magnetic flux.
Physics teacher, Secondary School No. 58, Sevastopol, Safronenko N.I.
Lesson topic: Faraday's experiments. Electromagnetic induction.
Laboratory work “Study 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 make observations natural phenomena, use simple measuring instruments to study physical phenomena.
- developing: develop logical thinking, cognitive interest, observation.
- educational: To form confidence in the possibility of knowing nature,necessityreasonable use of scientific achievements for the further development of human society, respect for the creators of science and technology.
Equipment: Electromagnetic induction: a coil with a galvanometer, a magnet, a coil with a core, a current source, a rheostat, a coil with a core through which alternating current flows, a solid and a ring with a slot, a coil with a light bulb. Film about M. Faraday.
Lesson type: combined lesson
Lesson method: partially search, explanatory and illustrative
Homework:
§21(pp.90-93), answer questions orally 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 induced current appear in a closed circuit (coil);
2) what determines the direction of the induction current;
3) what does the strength of the induction current depend on?
Equipment : milliammeter, coil, magnet
During the classes.
Connect the ends of the coil to the terminals of the milliammeter.
1. Find out what An electric current (induction) in a coil occurs when the magnetic field inside the coil changes. Changes in the magnetic field inside the coil can be caused by moving 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 moves, does a current (induction) appear in the coil? (When the magnetic field changes, does an induced 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 added 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 direction of deflection of the milliammeter needle:
Magnet poles
To reel
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 reading.
Quickly insert the magnet into the coil. Observe the milliammeter reading.
Conclusion.
During the classes
The road to knowledge? She's easy to understand. You can simply answer: “You make mistakes and make mistakes again, but less, less each time. I hope that today's lesson will be one less on this road 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. It is a rare case when the date of a new remarkable discovery is known so accurately!
The phenomenon of electromagnetic induction is the phenomenon of the occurrence of electric current in a closed conductor (coil) when the external magnetic field inside the coil changes. The current is called induction. Induction - guidance, receiving.
The purpose of the lesson: study the phenomenon of electromagnetic induction, i.e. under what conditions does an induction current appear in a closed circuit (coil); find out what determines the direction and magnitude of the induction current.
At the same time as studying 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 electric current creates a magnetic field around itself. Let's remember this experience again. (A student tells Oersted's experiment ). After this, the question arose about whether it was possible to obtain 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: “Convert magnetism into electricity.” And I walked towards my goal for almost ten years. He coped with the task brilliantly. As a reminder of what he should always think about, he carried a magnet in his pocket. With this lesson we will pay tribute to the great scientist.
Let's remember Michael Faraday. Who is he? (A student talks about M. Faraday ).
The son of a blacksmith, a newspaper delivery man, a book binder, a self-taught person who independently studied physics and chemistry from books, a laboratory assistant of the outstanding chemist Devi and finally a scientist, he did a lot of work, showed ingenuity, perseverance, and 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 largest experimentalist in the history of physics.
N S
1) 2)
SN
The magnet was inserted into the coil. When the magnet moved in the coil, a current (induction) was recorded. 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 device. 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 by the deviation of the magnetic needle they judged the flow of current. We will judge the current based on the readings of the milliammeter.
Students reproduce the experiment, perform step 1 in laboratory work. We noticed that the milliammeter needle deviates from its zero value, i.e. shows that a current appears 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 received an electric current using a changing magnetic field. This is the first merit of M. Faraday.
The second merit of M. Faraday is that he established what the direction of the induction current depends on. We will establish this too.Students perform step 2 in laboratory work. Let's turn to point 3 of the laboratory work. Let's find out that the strength of the induction current depends on the speed of movement of the magnet (the rate of change of the magnetic field in the coil).
What conclusions did M. Faraday make?
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 induction current is proportional to the rate of change of the magnetic field.
M. Faraday's second experiment:
I took two coils on a common core. I connected one to a milliammeter, and the second using a key to a current source. As soon as the circuit was closed, the milliammeter showed the induced current. When it opened, it also showed current. While the circuit is closed, i.e. there is current flowing in the circuit, the milliammeter did not show any current. The magnetic field exists, but does not change.
Let's consider a modern version of M. Faraday's experiments. We insert and remove an electromagnet and a core into a coil connected to a galvanometer, turn the current on and off, and use a rheostat to change the current strength. A coil with a light bulb is placed on the core of the coil through which alternating current flows.
Found out conditions occurrence of induction current in a closed circuit (coil). And what isreason its occurrence? Let us recall the conditions for the existence of 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 directional motion, thus creating an induction current.
The magnetic field changes, the number of magnetic field lines through a closed circuit changes. If you rotate the frame in a magnetic field, an induced 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 Electric Energy, which are located at energy industrial enterprises (power plants).A film about M. Faraday “From electricity to power generators” is shown from 12.02 minutes.
Transformers operate on the phenomenon of electromagnetic induction, with the help of which they transmit electricity without loss.A power line is on display.
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 (inhomogeneities in the beam distort the magnetic field and an induction current appears in the flaw detector coil).
I would like to remember the words of Helmholtz: “As long as people enjoy the benefits of electricity, they will remember the name of Faraday.”
“Let those be holy who, in creative fervour, exploring the whole world, discovered laws in it.”
I think that on our road of knowledge there are even fewer mistakes.
What new did you learn? (That current can be obtained using a changing magnetic field. We found out what the direction and magnitude of the induction current depends on).
What have you learned? (Receive induced current using a changing magnetic field).
Questions:
A magnet is pushed into the metal ring during the first two seconds, during the next two seconds it is motionless inside the ring, and during the next two seconds it is removed. At what time intervals does current flow in the coil? (From 1-2s; 5-6s).
A ring with or without a slot is put on the magnet. Where does induced current occur? (In a closed ring)
On the core of the coil, which is connected to an alternating current source, there is a ring. The current is turned on and the ring jumps. Why?
Board design:
"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 electric current in a closed conductor (coil) when the external magnetic field inside the coil changes.
This current is called induction current.
Lesson plan
Lesson topic: Laboratory work: “Study of the phenomenon of electromagnetic induction”
Type of lesson - mixed.
Type of activity combined.
Learning objectives of the lesson: study the phenomenon of electromagnetic induction
Lesson objectives:
Educational:study the phenomenon of electromagnetic induction
Developmental. 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 results: contribute to strengthening the practical orientation in teaching physics, developing the skills to apply acquired knowledge in various situations.
Personal: with promote the emotional perception of physical objects, the ability to listen, clearly and accurately express one’s thoughts, develop initiative and activity in solving physical problems, and develop the ability to work in groups.
Metasubject: pdevelop the ability to understand and use visual aids (drawings, models, diagrams). Developing an understanding of the essence of algorithmic instructions and the ability to act in accordance with the proposed algorithm.
Subject: about master physical language, the ability to recognize parallel and serial connections, the ability to navigate electrical diagram, collect diagrams. Ability to generalize and draw conclusions.
Progress of the lesson:
1. Organizing the beginning of the lesson (marking absentees, checking students’ readiness for the lesson, answering students’ questions about homework) - 2-5 min.
The teacher informs students about the topic of the lesson, formulates the objectives of the lesson and introduces students to the lesson plan. Students write down the topic of the lesson in their notebooks. The teacher creates conditions for motivating learning activities.
Mastering new material:
Theory. The phenomenon of electromagnetic inductionconsists in the occurrence of an electric current in a conducting circuit, which is either at rest 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 makes an angle to the plane of the conductorwith the direction of the magnetic induction vector.
Magnetic fluxФ through a surface of area S is a quantity equal to the product of the magnitude of the magnetic induction vector B by the area S and the cosine of the anglebetween vectors And .
Ф=В S cos α (1)
The direction of the inductive current arising in a closed loop when the magnetic flux through it changes is determined Lenz's rule: The inductive current arising in a closed circuit with its magnetic field counteracts the change in the magnetic flux that causes it.
Lenz's rule should be applied like this:
1. Set the direction of the magnetic induction lines B of the external magnetic field.
2. Find out whether the flux of magnetic induction 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 a surface bounded by a contour, extraneous forces appear in the latter, the action of which is characterized by emf, called Induction emf.
According to the law of electromagnetic induction, the induced emf in a closed loop is equal in magnitude to the rate of change of the magnetic flux through the surface bounded by the loop:
Instruments and equipment:galvanometer, power supply, core coils, arc-shaped magnet, key, connecting wires, rheostat.
Work order:
1. Obtaining induction current. To do 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, stationary relative to the first, while observing the direction of deflection of the galvanometer needle.
1.4. Move 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 whenever it moves, and the direction of the galvometer arrow 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 induced current occurs when the permanent magnet moves relative to the coil.
1.8. Draw a conclusion about the reason for the occurrence of induced current in the experiments performed.
2. Checking the fulfillment of Lenz's rule.
2.1. Repeat the experiment from point 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 Lenz's rule in each case and fill out Table 2.1 using this data.
Table 2.1.
N experience | Method for producing induction current | ||||
Inserting the north pole of a magnet into the coil | increases |
||||
Removing the North Pole of a Magnet from a Coil | decreases |
||||
Inserting the south pole of a magnet into the coil | increases |
||||
Removing the South Pole of a Magnet from a Coil | decreases |
3. Draw 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, for an inductive current to arise in it?
2. Explain why the inductive current in the circuit has such a direction that its magnetic field prevents the change in the magnetic flux that caused it?
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 change in the ring?
Admission to laboratory work 11
1.What is the force characteristic of a magnetic field called? Its graphic meaning.
2. How is the magnitude of the magnetic induction vector determined?
3. Define the unit of measurement of 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 magnetic flux. What is its graphic meaning?
7. Define the unit of measurement of 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 located 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.