test questions

1.What is electric capacity?

2. Define the following concepts: alternating current, amplitude, frequency, cyclic frequency, period, phase of oscillation

Laboratory work 11

Phenomenon study 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; generator model electric current(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, whether the modulus of the induction vector B is the same magnetic field 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 fast or slow change magnetic flux through the coil in it there was a larger current in modulus?

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 electrical circuit, it generates an alternating current.

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">.!}

2. There is no coil in the circuit: hence .

For from formulas (6), (7), and (14), respectively, we have

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

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

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

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

Note that the lines of magnetic induction come out of 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.

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 to the subject, to 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 own 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 min.

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, calledEMF 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 one, 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.

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.

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

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