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. 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.). 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 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 oscillations. Thus, a sinusoidal alternating current has a period T- the time of one complete oscillation and the frequency v number of complete oscillations per unit of time. There is a relationship between these quantities
The AC circuit, unlike the DC circuit, allows the inclusion of a capacitor.
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called full resistance or impedance chains. Therefore, expression (8) is called Ohm's law for alternating current.
In this work, active resistance R coil is determined using Ohm's law for a section of a DC circuit.
Let's consider two special cases.
1. There is no capacitor in the circuit. This means that the capacitor is turned off and instead the circuit is closed by a conductor, the potential drop on which is practically zero, that is, the value U in equation (2) is zero..gif" alt="(!LANG:http://web-local.rudn.ru/web-local/uem/ido/8/Image474.gif" width="54" height="18">.!}
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2. There is no coil in the circuit: Consequently .
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 
Michael Faraday was the first to study the phenomenon of electromagnetic induction. More precisely, he established and investigated this phenomenon in search of ways to turn magnetism into electricity.
It took him ten years to solve such a problem, but now we use the fruits of his work everywhere, and we cannot imagine modern life without the use of electromagnetic induction. In the 8th grade, we already considered this topic, in the 9th grade this phenomenon is considered in more detail, but the derivation of formulas refers to the 10th grade course. You can follow this link to get acquainted with all aspects of this issue.
The phenomenon of electromagnetic induction: consider the experience
We will consider what constitutes the phenomenon of electromagnetic induction. You can conduct an experiment for which you need a galvanometer, a permanent magnet and a coil. By connecting the galvanometer to the coil, we push a permanent magnet inside the coil. In this case, the galvanometer will show the change in current in the circuit.
Since we do not have any current source in the circuit, it is logical to assume that the current arises due to the appearance of a magnetic field inside the coil. When we pull the magnet back out of the coil, we will see that the readings of the galvanometer will change again, but its needle will deviate in the opposite direction. We will again receive a current, but already directed in the other direction.
Now we will do a similar experiment with the same elements, only at the same time we will fix the magnet motionless, and we will now put the coil itself on and off the magnet, connected to the galvanometer. We will get the same results. The pointer of the galvanometer will show us the appearance of current in the circuit. In this case, when the magnet is stationary, there is no current in the circuit, the arrow stands at zero.
It is possible to carry out a modified version of the same experiment, only to replace the permanent magnet with an electric one, which can be turned on and off. We will get results similar to the first experience when the magnet moves inside the coil. But, in addition, when turning off and turning off a stationary electromagnet, it will cause a short-term appearance of current in the coil circuit.
The coil can be replaced by a conducting circuit and experiments can be done on moving and rotating the circuit itself in a constant magnetic field, or a magnet inside a fixed circuit. The results will be the same appearance of current in the circuit when the magnet or circuit moves.
A change in the magnetic field causes a current to appear
From all this it follows that a change in the magnetic field causes the appearance of an electric current in the conductor. This current is no different from the current that we can get from batteries, for example. But to indicate the cause of its occurrence, such a current was called induction.
In all cases, we changed the magnetic field, or rather, the magnetic flux through the conductor, as a result of which a current arose. Thus, the following definition can be derived:
With any change in the magnetic flux penetrating the circuit of a closed conductor, an electric current arises in this conductor, which exists during the entire process of changing the magnetic flux.
The student must:
be able to: handle physical instruments and use them in laboratory work; to investigate the phenomenon of electromagnetic induction - to determine what the magnitude and direction of the induction current depend on; 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 the conductor resistance on temperature.
Security of the lesson
Equipment and tools: milliammeter, coil-coil, arcuate magnet, strip magnet, DC power supply, 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 bounded by the loop. Changing the magnetic flux through the circuit can be done in two different ways:
1) change in time of the magnetic field in which the fixed circuit is located when the magnet is pushed into the coil or when it is 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 take it off the north pole of the arcuate magnet at different speeds (see figure), and for each case note the maximum and minimum strength of the induction current and the direction of deviation of the device arrow.
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 a faster rate. Pay attention to where the needle of the milliammeter deviated this time.
2. Fold two magnets (stripe and arcuate) with the same poles and repeat the experiment with different speeds of the magnets in the coil.
3. Connect to the clamps of the milliammeter instead of the coil a long wire, folded into several turns. Putting on and taking off turns of wire from the pole of the arcuate magnet, note the maximum strength of the induction current. Compare it with the maximum strength of the induction current obtained in experiments with the same magnet and coil, and find the dependence of the induction 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 to the minimum resistance of the rheostat. Close the circuit with a key, watching the milliammeter needle;
b) open the circuit with the key. What changed?
c) put the rheostat slider in the middle position. Repeat the experience;
d) set the slider of the rheostat 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.
Lab #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.
Security of the lesson
Equipment and tools: adjustable alternating voltage source, collapsible laboratory transformer, AC voltmeters (or avometer), key, connecting wires;
Handouts: these guidelines for the implementation of laboratory work.
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 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 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, arcuate 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 |
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Removing the magnet's north pole from the coil | decreases |
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Insertion of the south pole of the magnet into the coil | increases |
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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.
