- " 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
Lab #9
Studying the phenomenon of electromagnetic induction
Objective: to study the conditions for the occurrence of induction current, induction EMF.
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 a magnetic field it is possible to obtain an electric current in a conductor.
The phenomenon of electromagnetic inductionconsists in the occurrence of an electric current in a closed circuit when the magnetic flux penetrating the circuit changes.
The current that occurs during the phenomenon of electromagnetic induction is called induction.
In the electrical circuit (Figure 1), an induction current occurs if there is a 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 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 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, the direction of the magnetic field lines is opposite to the lines of force of the 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 the right 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 inductive current will coincide in direction with the lines of force of the permanent magnet, and the current will flow from right to left.
Progress.
Prepare a table for the report and fill it in as the experiments are carried out.
|
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) |
|
|
Quickly insert the magnet into the coil with the north pole |
|
|||
|
Leave the magnet in the coil stationary after experience 1 |
|
|||
|
Quickly pull the magnet out of the coil |
|
|||
|
Move the coil quickly 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 north pole magnet into the coil |
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).
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, 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 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 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 a 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 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.
https://pandia.ru/text/80/343/images/image073.gif" alt="(!LANG:http://web-local.rudn.ru/web-local/uem/ido/8/Image443 .gif" width="89" height="24">,!}
|
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">.!}
|
|
2. There is no coil in the circuit: Consequently .
For from formulas (6), (7), and (14), respectively, we have
Lesson plan
Lesson topic: Laboratory work: "Studying the phenomenon of electromagnetic induction"
Type of occupation - mixed.
Lesson type combined.
Learning objectives of the lesson: to study the phenomenon of electromagnetic induction
Lesson objectives:
Educational:study the phenomenon of electromagnetic induction
Developing. To develop the ability to observe, form an idea of the process of scientific knowledge.
Educational. Develop cognitive interest in the subject, develop the ability to listen and be heard.
Planned educational results: to contribute to strengthening the practical orientation in teaching physics, the formation of skills to apply the acquired knowledge in various situations.
Personality: with contribute to the emotional perception of physical objects, the ability to listen, clearly and accurately express their thoughts, develop initiative and activity in solving physical problems, form the ability to work in groups.
Metasubject: pdevelop the ability to understand and use visual aids (drawings, models, diagrams). Development of an understanding of the essence of algorithmic prescriptions and the ability to act in accordance with the proposed algorithm.
subject: about know the physical language, the ability to recognize parallel and serial connections, the ability to navigate in an electrical circuit, to assemble circuits. Ability to generalize and draw conclusions.
Lesson progress:
1. Organization of the beginning of the lesson (marking absentees, checking students' readiness for the lesson, answering students' questions on homework) - 2-5 minutes.
The teacher tells the students the topic of the lesson, formulates the objectives of the lesson and introduces the students to the lesson plan. Students write the topic of the lesson in their notebooks. The teacher creates conditions for the motivation of learning activities.
Mastering new material:
Theory. The phenomenon of electromagnetic inductionconsists in the occurrence of an electric current in a conducting circuit, which either rests in an alternating magnetic field, or moves in a constant magnetic field in such a way that the number of magnetic induction lines penetrating the circuit changes.
The magnetic field at each point in space is characterized by the magnetic induction vector B. Let a closed conductor (circuit) be placed in a uniform magnetic field (see Fig. 1.)
Picture 1.
Normal to the plane of the conductor makes an anglewith the direction of the magnetic induction vector.
magnetic fluxФ through a surface with an area S is called a value equal to the product of the modulus of the magnetic induction vector B and the area S and the cosine of the anglebetween vectors and .
Ф=В S cos α (1)
The direction of the inductive current that occurs in a closed circuit when the magnetic flux through it changes is determined by Lenz's rule: the inductive current arising in a closed circuit counteracts with its magnetic field the change in the magnetic flux by which it is caused.
Apply Lenz's rule as follows:
1. Set the direction of the lines of magnetic induction B of the external magnetic field.
2. Find out if the magnetic induction flux of this field increases through the surface bounded by the contour ( F 0), or decreases ( F 0).
3. Set the direction of the lines of magnetic induction B "magnetic field
inductive current Iusing the gimlet rule.
When the magnetic flux changes through the surface bounded by the contour, external forces appear in the latter, the action of which is characterized by the EMF, called EMF of induction.
According to the law of electromagnetic induction, the EMF of induction in a closed loop is equal in absolute value to the rate of change of the magnetic flux through the surface bounded by the loop:
Devices and equipment:galvanometer, power supply, core coils, arched magnet, key, connecting wires, rheostat.
Work order:
1. Obtaining an induction current. For this you need:
1.1. Using Figure 1.1., assemble a circuit consisting of 2 coils, one of which is connected to a DC source through a rheostat and a key, and the second, located above the first, is connected to a sensitive galvanometer. (see fig. 1.1.)
Figure 1.1.
1.2. Close and open the circuit.
1.3. Make sure that the induction current occurs in one of the coils at the moment of closing the electrical circuit of the coil, which is stationary relative to the first, while observing the direction of deviation of the galvanometer needle.
1.4. Set in motion a coil connected to a galvanometer relative to a coil connected to a direct current source.
1.5. Make sure that the galvanometer detects the occurrence of an electric current in the second coil with any movement of it, while the direction of the arrow of the galvanometer will change.
1.6. Perform an experiment with a coil connected to a galvanometer (see Fig. 1.2.)
Figure 1.2.
1.7. Make sure that the induction current occurs when the permanent magnet moves relative to the coil.
1.8. Make a conclusion about the cause of the induction current in the experiments performed.
2. Checking the fulfillment of the Lenz rule.
2.1. Repeat the experiment from paragraph 1.6. (Fig. 1.2.)
2.2. For each of the 4 cases of this experiment, draw diagrams (4 diagrams).
Figure 2.3.
2.3. Check the fulfillment of the Lenz rule in each case and fill in Table 2.1 according to these data.
Table 2.1.
N experience | Method for obtaining induction current | ||||
Adding the North Pole of a Magnet to the Coil | increases |
||||
Removing the magnet's north pole from the coil | decreases |
||||
Insertion of the south pole of the magnet into the coil | increases |
||||
Removing the South Pole of the Magnet from the Coil | decreases |
3. Make a conclusion about the laboratory work done.
4. Answer security questions.
Test questions:
1. How should a closed circuit move in a uniform magnetic field, translationally or rotationally, so that an inductive current arises in it?
2. Explain why the inductive current in the circuit has such a direction that its magnetic field prevents a change in the magnetic flux of its cause?
3. Why is there a "-" sign in the law of electromagnetic induction?
4. A magnetized steel bar falls through a magnetized ring along its axis, the axis of which is perpendicular to the plane of the ring. How will the current in the ring change?
Admission to laboratory work 11
1. What is the name of the power characteristic of the magnetic field? Its graphic meaning.
2. How is the modulus of the magnetic induction vector determined?
3. Give the definition of the unit of measurement of the magnetic field induction.
4. How is the direction of the magnetic induction vector determined?
5. Formulate the gimlet rule.
6. Write down the formula for calculating the magnetic flux. What is its graphic meaning?
7. Define the unit of measure for magnetic flux.
8. What is the phenomenon of electromagnetic induction?
9. What is the reason for the separation of charges in a conductor moving in a magnetic field?
10. What is the reason for the separation of charges in a stationary conductor in an alternating magnetic field?
11. Formulate the law of electromagnetic induction. Write down the formula.
12. Formulate Lenz's rule.
13. Explain Lenz's rule based on the law of conservation of energy.
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 the same electric charge transferred through the wire section of the coil?
2. Will there be an induction current in the rubber ring when a magnet is introduced into it?
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 follow 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.
