«Magnetic field and its graphic representation. Inhomogeneous and uniform magnetic fields»
The purpose of the lesson: providing conditions for students to acquire knowledge about the magnetic fieldcallowanceahegographic image
Tasks:
educational:
reveal the existence of a magnetic field in the process of solving the situation;
define the magnetic field;
to investigate the dependence of the magnitude of the magnetic field of the magnet on the distance to it;
explore the interaction of the poles of two magnets;
find out the properties of the magnetic field;
to get acquainted with the image of the magnetic field through the lines of force.
developing: development of logical thinking; ability to analyze, compare, systematize information;
educational: develop teamwork skills;
form responsibility in the implementation of the educational task.
Lesson type: learning new material.
Equipment: magnets (strip, arcuate) according to the number of students, iron filings, white sheet.
During the classes
1) Organizational stage. The motto of our lesson will be the words of R. Descartes: "... In order to improve the mind, you need to think more than memorize."
2) Setting the goal and objectives of the lesson. Motivation of educational activity of students.
Situation. It was many centuries ago. In search of a sheep, the shepherd went to unfamiliar places, to the mountains. There were black stones all around. He noticed with amazement that his iron-tipped stick was being pulled towards the stones, as if some invisible hand was grasping and holding it. Struck by the miraculous power of the stones, the shepherd brought them to the nearest town. Here everyone could be convinced that the shepherd's story was not a fiction - amazing stones attracted iron things to themselves! Moreover, it was worth rubbing the knife blade with such a stone, and he himself began to attract iron objects: nails, arrowheads. As if from a stone brought from the mountains, some kind of power, of course, mysterious, flowed into them.
Loving stone "- such a poetic name was given by the Chinese to this stone. A loving stone (tshu-shih), the Chinese say, attracts iron, just as a tender mother attracts her children.
Teacher. What stone is the story about? (About the magnet.)
Bodies that remain magnetized for a long time are called permanent magnets Or just magnets.
Teacher. You have magnets on your desks. I suggest taking the magnets and bringing them to each other without touching. What are you observing? How do you explain? Why do magnets interact? It turns out that there is something between the magnets that we cannot see and cannot touch with our hands. Then it is called a special form of matter - a field. magnetic field. We find out the topic of the lesson and set the goal of the lesson - the study of the magnetic field. Not just the concept of a magnetic field, but its properties.
3 ) Primary assimilation of new knowledge.
So write down the topic in your notebook. Magnetic field and its graphic representation. Inhomogeneous and uniform magnetic fields. The purpose of our lesson: to identify the basic properties of the magnetic field and how to display it
So a little about magnets (website INFOOUROK, Magnetic field)
(when watching the film, we write down the definitions, properties of the field, make sketches)
A magnetic field - special form of matter ( force field) that is formed around moving charged particles)
1. The magnetic field is generated only by moving charges.
2. The magnetic field is invisible, but material. It can be detected only by the effect that it has.
3. A magnetic field can be detected by its effect on a magnetic needle and on other moving bodies.
You can depict a magnetic field using magnetic lines.
Magnetic lines are imaginary lines along which small magnetic needles would be placed in a magnetic field.
We can see them by doing an experiment with iron filings.
Experience: On a white sheet, under which there is a magnet, slowly pour iron filings. The sawdust lines up along the lines of the magnetic field.
Please note that in those areas where the magnetic field is stronger - at the poles, the magnetic lines are closer to each other, i.e. thicker. Than in those places where the field is weaker.
Features of magnetic lines (write down)
1. Magnetic lines can be drawn through any point in space.
2. They are closed and do not intersect. The middle line goes on forever.
3. The magnetic line is drawn so that the tangent at each point of the line coincides with the axis of the magnetic needle placed at this point.
4. The direction of the north pole of the compass needles located along this line is taken as the direction of the magnetic line.
5. A stronger magnetic field is represented by a higher concentration.
Consider the lines of force of a coil with current. We have been familiar with the concept of a solenoid since grade 8 .
Solenoid- this is a coil in the form of an insulated conductor wound on a cylindrical surface, through which an electric current flows (show)
Arrow rule (depict in a notebook)
Homogeneous field (depict in a notebook)
Inhomogeneous field (depict in a notebook)
4 ) Initial check of understanding fill in the tables
| The result is a graphical representation of magnetic field lines |
|
| Bar magnet | |
| arcuate magnet |
| Non-uniform magnetic field | Uniform magnetic field |
|
| Line arrangement | Curved, their density is different | Parallel, their density is the same |
| Line Density | not the same | the same |
| not the same | the same |
5 ) Primary pinning. Independent work with peer review.
1. The rotation of the magnetic needle near the conductor with current is explained by the fact that it is affected by ...
A. ... a magnetic field created by charges moving in a conductor.
B. ... an electric field created by the charges of a conductor.
B. ... an electric field created by charges moving in a conductor.
2. Magnetic fields are created...
A. ... both stationary and moving electric charges.
B. ... immobile electric charges.
B. ... moving electric charges.
3. Magnetic field lines are ...
A. ... lines that match the shape of the magnet.
B. ... lines along which a positive charge moves when it enters a magnetic field.
B. ... imaginary lines along which small magnetic needles would be placed, placed in a magnetic field.
4. Lines of a magnetic field in space outside a permanent magnet ...
A. ...begin at the north pole of the magnet, end at infinity.
B. ... start at the north pole of the magnet, end at the south.
B. ... start at the pole of the magnet, end at infinity.
G. ...begin at the south pole of the magnet, end at the north.
5. The configurations of the lines of the magnetic field of the solenoid are similar to the pattern of lines of force ...
A. ... a bar magnet.
B. ...a horseshoe magnet.
B. ... a straight wire with current.
Benchmarking and self-assessment:
3 correct answers - score 3,
4 correct answers - score 4,
5 correct answers - score 5.
6) Information about homework, instructions for its implementation
7) Reflexion (summing up the lesson)
Choose the beginning of the phrase and continue the sentence.
I'll try…
surprised me...
gave me a lesson for life...
Permanent magnets N - the north pole of the magnet S - the south pole of the magnet Permanent magnets Permanent magnets are bodies that retain magnetization for a long time. Arcuate magnet Bar magnet N N S S Pole - the place of the magnet where the strongest action is found
Hypothesis of Ampère ++ e - SN According to the hypothesis of Ampère (r.), ring currents arise in atoms and molecules as a result of the movement of electrons. In 1897 the hypothesis was confirmed by the English scientist Thomson, and in 1910. American scientist Milliken measured the currents. What are the reasons for magnetization? When a piece of iron is introduced into an external magnetic field, all elementary magnetic fields in this iron are oriented in the same way in the external magnetic field, forming their own magnetic field. So a piece of iron becomes a magnet.
Magnetic field of permanent magnets Magnetic field is the component of the electromagnetic field that appears in the presence of a time-varying electric field. In addition, the magnetic field can be created by the current of charged particles. An idea of the form of the magnetic field can be obtained using iron filings. One has only to put a sheet of paper on the magnet and sprinkle it with iron filings on top.
Magnetic fields are depicted using magnetic lines. These are imaginary lines along which magnetic needles are placed in a magnetic field. Magnetic lines can be drawn through any point of the magnetic field, they have a direction and are always closed. Outside the magnet, magnetic lines exit the north pole of the magnet and enter the south pole, closing inside the magnet.
INHOMOGENEOUS MAGNETIC FIELD The force with which the magnet field acts can be different both in absolute value and in direction. Such a field is called inhomogeneous. Characteristics of an inhomogeneous magnetic field: magnetic lines are curved; the density of the magnetic lines is different; the force with which the magnetic field acts on the magnetic needle is different at different points of this field in magnitude and direction.
Where does an inhomogeneous magnetic field exist? Around a straight conductor with current. The figure shows a section of such a conductor, located perpendicular to the plane of the drawing. The current is directed away from us. It can be seen that the magnetic lines are concentric circles, the distance between which increases with distance from the conductor
HOMOGENEOUS MAGNETIC FIELD Characteristics of a uniform magnetic field: magnetic lines are parallel straight lines; the density of magnetic lines is the same everywhere; the force with which the magnetic field acts on the magnetic needle is the same at all points of this field in magnitude and direction.
If a powerful flare occurs on the Sun, then the solar wind intensifies. This disturbs the earth's magnetic field and results in a magnetic storm. Solar wind particles flying past the Earth create additional magnetic fields. Magnetic storms cause serious harm: they have a strong effect on radio communications, on telecommunication lines, many measuring instruments show incorrect results. It is interesting
The Earth's magnetic field reliably protects the Earth's surface from cosmic radiation, whose effect on living organisms is destructive. The composition of cosmic radiation, in addition to electrons, protons, includes other particles moving in space at great speeds. It is interesting
The result of the interaction of the solar wind with the Earth's magnetic field is the aurora. Invading the Earth's atmosphere, the particles of the solar wind (mainly electrons and protons) are guided by the magnetic field and are focused in a certain way. Colliding with the atoms and molecules of atmospheric air, they ionize and excite them, resulting in a glow, which is called the aurora. It is interesting
The study of the influence of various factors of weather conditions on the body of a healthy and sick person is carried out by a special discipline - biometrology. Magnetic storms cause discord in the work of the cardiovascular, respiratory and nervous systems, and also change the viscosity of the blood; in patients with atherosclerosis and thrombophlebitis, it becomes thicker and coagulates faster, while in healthy people, on the contrary, it increases. It is interesting
1. What bodies are called permanent magnets? 2. What generates the magnetic field of a permanent magnet? 3. What is called the magnetic poles of a magnet? 4. What is the difference between homogeneous magnetic fields and inhomogeneous ones? 5. How do the poles of magnets interact with each other? 6. Explain why the needle attracts the paper clip? (see pic) Fastening
Plan outline of lesson number 16.
Lesson topic: “Magnetic field and its graphic representation. Inhomogeneous and uniform magnetic field»
Goals:
Educational : to establish a relationship between the direction of the magnetic lines of the magnetic field of the current and the direction of the current in the conductor. Introduce the concept of inhomogeneous and uniform magnetic fields. In practice, get a picture of the lines of force of the magnetic field of a permanent magnet, solenoid, conductor through which an electric current flows. Systematize knowledge on the main issues of the topic “Electromagnetic field”, continue to teach how to solve qualitative and experimental problems.
Educational : to intensify the cognitive activity of students in physics lessons. To develop the cognitive activity of students.
Educational : to promote the formation of the idea of the cognizability of the world. To cultivate industriousness, mutual understanding between students and the teacher.
Tasks:
educational : deepening and expanding knowledge about the magnetic field, substantiate the relationship between the direction of the magnetic lines of the magnetic field of the current and the direction of the current in the conductor.
Educational : to show causal relationships in the study of the magnetic field of direct current and magnetic lines, that causeless phenomena do not exist, that experience is a criterion for the truth of knowledge.
Educational : to continue work on the formation of skills to analyze and generalize knowledge about the magnetic field and its characteristics. Involving students in active practical activities when performing experiments.
Equipment: presentation,table, projector, screen, mmagnetic arrows, iron filings, magnets, compass.
Lesson plan:
Organizational moment. (1-2 min)
Motivation and goal setting (1-2 min)
Learning a new topic (15-30 min)
4. Homework. (1-2 min)
1. Organizational moment.
They got up, lined up. Hello, have a seat.
2. Motivation and goal setting.
Each of you watched how at the end of summer, at the beginning of autumn, many birds fly away to warmer climes. Migratory birds cover great distances, fearing the winter cold, and in the spring they return. Birds navigate by the Earth's magnetic field. So this days we will talk about magnets, consider the properties of a magnet. Let's remember what a magnetic field is, what magnetic fields are.
3. Studying a new topic.
The history of the magnet has more than two and a half thousand years.
An old legend tells of a shepherd named Magnus. He once discovered that the iron tip of his stick and the nails of his boots were attracted to the black stone. This stone became known as the "Magnus" stone or simply "magnet". But another legend is also known that the word "magnet" came from the name of the area where iron ore was mined (the hills of Magnesia in Asia Minor) slide 2 . Thus, for many centuries BC. it was known that some rocks have the property of attracting pieces of iron. This was mentioned in VI in BC Greek physicist Thales. In those days, the properties of magnets seemed magical. in the same ancient Greece, their strange action was directly connected with the activity of the Gods.
Here is how the ancient Greek sage Socrates described the property of this stone: “This stone not only attracts an iron ring, it endows the ring with its power, so that it, in turn, can attract another ring, and thus many rings and pieces of iron can hang on top of each other ! This is due to the power of the magnetic stone."
What are the properties of magnets and what determines the properties of magnets? To do this, let's look at the experience. We take a sheet of paper, a magnet and iron filings. What are we seeing? Video
slide 3
And if you take 2 magnets and bring them to each other with the same poles? how will they behave? And if opposite poles?
Why are pieces, iron filings attracted to a magnet? Just as a glass rod attracts pieces of paper, so a magnet attracts iron filings. There is a magnetic field around a magnet.
From the 8th grade physics course, you learned that a magnetic field is generated by an electric current. It exists, for example, around a metal conductor with current. In this case, the current is created by electrons moving in a direction along the conductor.
Since electric current is a directed movement of charged particles, we can say thatthe magnetic field is created by moving charged particles, both positive and negative.
So let's write the definition:
A magnetic field is a special kind of matter that is created around magnets by moving charged particles, both positive and negative.
slide 5
Remember that if the particles are moving, then a magnetic field is created. We said that m.p. is a special kind of matter, it is called a special kind, because. not perceived by the senses.
To detect m.p. magnetic arrows are used.
To visually represent the magnetic field, we use magnetic lines (they are also called magnetic field lines). Recall thatmagnetic lines - these are imaginary lines along which small magnetic needles placed in a magnetic field would be located. Slide
A magnetic line can be drawn through any point in space where a magnetic field exists.
Figure 86,a, b it is shown that a magnetic line (both rectilinear and curvilinear) is drawn so that at any point of this line the tangent to it coincides with the axis of the magnetic needle placed at this point. slide 6
Magnetic lines are closed. For example, the picture of the magnetic lines of a straight conductor with current is a concentric circle lying in a plane perpendicular to the conductor.Slide 7
In those regions of space where the magnetic field is stronger, the magnetic lines are drawn closer to each other, i.e., thicker than in those places where the field is weaker. For example, the field shown in Figure 87 is stronger on the left than on the right.Slide 8
Thus, according tothe picture of the magnetic lines, one can judge not only the direction, but also the magnitude of the magnetic field (i.e., at what points in space the field acts on the magnetic needle with greater force, and at what points with less).
Let's look at fig. 88 in the textbook: a conductor with a current BC is shown, let's remember what an email is. current - charge movement. particles, and we said, if the particles move, then a magnetic field is created. Let's look at the pointNwill there be a magnetic field? Yes, it will, because current flows throughout the conductor. At what point A or M will the magnetic field be stronger? At point A, since it is closer to the magnet.
There are two types of magnetic field: homogeneous and non-uniform. Let's look at these types of magnetic fields.
Magnetic lines have neither beginning nor end: they are either closed or go from infinity to infinity. Rice. 89
Outside the magnet, magnetic lines are densest at its poles. This means that the field is strongest near the poles, and as you move away from the poles, it weakens. The closer to the pole of the magnet the magnetic needle is located, the greater the modulus of force the field of the magnet acts on it. Since the magnetic lines are curved, the direction of the force with which the field acts on the needle also changes from point to point.
Thus,the force with which the field of a strip magnet acts on a magnetic needle placed in this field at different points in the field can be different both in absolute value and in direction.
Slide 9
Such a field is calledheterogeneous. The lines of an inhomogeneous magnetic field are curved, their density varies from point to point.
Another example of a non-uniform magnetic field is the field around a rectilinear current-carrying conductor. Figure 90 shows a section of such a conductor, located perpendicular to the plane of the drawing. The circle indicates the cross section of the conductor. From this figure it can be seen that the magnetic lines of the field created by a rectilinear conductor with current are concentric circles, the distance between which increases with distance from the conductor.
In some limited area of space, you can createhomogeneous magnetic field, i.e.field, at any point in which the force acting on the magnetic needle is the same in magnitude and direction.
slide 10.
Figure 91 shows a uniform field that occurs inside the so-called solenoid, i.e., a cylindrical wire coil with current. The field inside the solenoid can be considered homogeneous if the length of the solenoid is much greater than its diameter (outside the solenoid, the field is inhomogeneous, its magnetic lines are approximately the same as those of a bar magnet). From this figure, we see thatmagnetic lines of a uniform magnetic field are parallel to each other and are located with the same density. The field inside the permanent bar magnet in its central part is also homogeneous (see Fig. 89).
slide11
For the image of the magnetic field, the following method is used. If the lines of a uniform magnetic field are located perpendicular to the plane of the drawing and are directed from us beyond the drawing, then they are depicted with crosses (Fig. 92), and if because of the drawing towards us, then with dots (Fig. 93). As in the case of current, each cross is, as it were, the tail of an arrow flying from us, and the point is the tip of an arrow flying towards us (in both figures, the direction of the arrows coincides with the direction of the magnetic lines).
Since birds still orient themselves in space during flights, it turns out that the Earth is surrounded by a magnetic field. Inside the earth is a large magnet which creates a huge magnetic field around the earth. And the magnet inside the earth is the iron ore from which our permanent magnets are made. Scientists say that carrier pigeons, for example, also have a kind of magnet inside, which is why they are so well oriented in space.
Homework.
Paragraph 43, 44. exercise 34.
Prepare messages on the topic: “M.p. Earth”, “M.p. in living organisms", "Magnetic storms".
Permanent magnets are bodies that retain magnetization for a long time. Pole - the place of the magnet where the strongest action is found N - the north pole of the magnet S - the south pole of the magnet S N S Arcuate magnet Bar magnet N 2
What are the reasons for magnetization? Hypothesis of Ampère + S According to the hypothesis of Ampère (1775 - 1836), ring currents arise in atoms and molecules as a result of the movement of electrons. In 1897, the English scientist Thomson confirmed the hypothesis, and in 1910 the American scientist Milliken measured the currents. - e N When a piece of iron is introduced into an external magnetic field, all elementary magnetic fields in this iron are oriented in the same way in the external magnetic field, forming their own magnetic field. So a piece of iron becomes a magnet. 3
The movement of electrons is a circular current, and around a conductor with electric current there is a magnetic field. 4 4
Artificial and natural magnets. Artificial magnets - obtained by magnetizing iron when it is introduced into a magnetic field. Natural magnets are magnetic iron ore. Natural magnets, i.e. pieces of magnetic iron ore magnetite 5
Properties of magnets: 1. The strongest magnetic action is found at the poles of magnets; 2. Cast iron, steel, iron and some alloys are well attracted by a magnet; 3. Iron, steel, nickel in the presence of magnetic iron ore acquire magnetic properties; 4. Opposite magnetic poles attract, like ones repel. 6 6
The interaction of magnets is explained by the fact that any magnet has a magnetic field, and these magnetic fields interact with each other. 7
The magnetic field of permanent magnets An idea of the form of a magnetic field can be obtained using iron filings. One has only to put a sheet of paper on the magnet and sprinkle it with iron filings on top. Magnetic field - a component of the electromagnetic field that appears in the presence of a time-varying electric field. In addition, the magnetic field can be created by the current of charged particles. eight
Magnetic fields are depicted using magnetic lines. These are imaginary lines along which magnetic needles are placed in a magnetic field. Magnetic lines can be drawn through any point of the magnetic field, they have a direction and are always closed. Outside the magnet, magnetic lines exit the north pole of the magnet and enter the south pole, closing inside the magnet. nine
According to the pattern of magnetic lines, one can judge not only the direction, but also the magnitude of the magnetic field. In those regions of space where the magnetic field is stronger, the magnetic lines are drawn closer to each other, thicker than in those places where the field is weaker. ten
INHOMOGENEOUS MAGNETIC FIELD The force with which the magnet field acts can be different both in absolute value and in direction. Such a field is called inhomogeneous. Characteristics of an inhomogeneous magnetic field: magnetic lines are curved; the density of the magnetic lines is different; the force with which the magnetic field acts on the magnetic needle is different at different points of this field in magnitude and direction. 12
Where does an inhomogeneous magnetic field exist? Around a straight conductor with current. The figure shows a section of such a conductor, located perpendicular to the plane of the drawing. The current is directed away from us. It can be seen that the magnetic lines are concentric circles, the distance between which increases with distance from the conductor 13
HOMOGENEOUS MAGNETIC FIELD Characteristics of a uniform magnetic field: magnetic lines are parallel straight lines; the density of magnetic lines is the same everywhere; the force with which the magnetic field acts on the magnetic needle is the same at all points of this field in magnitude and direction. fifteen
Where does a uniform magnetic field exist? Inside the bar magnet and inside the solenoid, if its length is much greater than the diameter 16
This is interesting The magnetic poles of the Earth have changed places many times (inversions). This has happened 7 times in the last million years. 570 years ago, the Earth's magnetic poles were located at the equator 17
This is interesting. If a powerful flare occurs on the Sun, then the solar wind intensifies. This disturbs the earth's magnetic field and results in a magnetic storm. Solar wind particles flying past the Earth create additional magnetic fields. Magnetic storms cause serious harm: they have a strong effect on radio communications, on telecommunication lines, many measuring instruments show incorrect results. eighteen
This is interesting. The Earth's magnetic field reliably protects the Earth's surface from cosmic radiation, whose effect on living organisms is destructive. The composition of cosmic radiation, in addition to electrons, protons, includes other particles moving in space at great speeds. nineteen
This is interesting The result of the interaction of the solar wind with the Earth's magnetic field is the aurora. Invading the Earth's atmosphere, the particles of the solar wind (mainly electrons and protons) are guided by the magnetic field and are focused in a certain way. Colliding with the atoms and molecules of atmospheric air, they ionize and excite them, resulting in a glow, which is called the aurora. 20
This is interesting. A special discipline - biometrology - is engaged in studying the influence of various weather factors on the body of a healthy and sick person. Magnetic storms cause discord in the work of the cardiovascular, respiratory and nervous systems, and also change the viscosity of the blood; in patients with atherosclerosis and thrombophlebitis, it becomes thicker and coagulates faster, while in healthy people, on the contrary, it increases. 21
Fixing 1. 2. 3. 4. 5. 6. What bodies are called permanent magnets? What generates the magnetic field of a permanent magnet? What are the magnetic poles of a magnet? What is the difference between uniform magnetic fields and non-uniform ones? How do the poles of magnets interact with each other? Explain why the needle attracts the paperclip? (see pic) 22
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