«Magnetic field and its graphic representation. Heterogeneous and homogeneous 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 logical thinking; ability to analyze, compare, systematize information;
educational: develop teamwork skills;
create accountability for the implementation learning task.
Lesson type: learning new material.
Equipment: magnets (strip, arcuate) according to the number of students, iron filings, White list.
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 learning activities 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 stick with an iron tip was attracted by the stones, as if it were being grabbed and held by some kind of invisible hand. Stricken miraculous power the shepherd brought the stones 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.)
body, long time retaining magnetization 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. Average line goes endlessly.
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 flows electricity(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. ... electric field created by the charges of the 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. ... the lines along which it moves positive charge, falling into a magnetic field.
B. ... imaginary lines along which small magnetic needles would be placed, placed in a magnetic field.
4. Magnetic field lines in space outside 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...
Magnetic field and its characteristics. When an electric current passes through a conductor, a a magnetic field. A magnetic field is one of the types of matter. It has an energy that manifests itself in the form electromagnetic forces acting on individual moving electric charges(electrons and ions) and their flows, i.e. electric current. Under the influence of electromagnetic forces, moving charged particles deviate from their original path in a direction perpendicular to the field (Fig. 34). The magnetic field is formed only around moving electric charges, and its action also extends only to moving charges. Magnetic and electric fields are inseparable and form together a single electromagnetic field. Any change electric field leads to the appearance of a magnetic field and, conversely, any change in the magnetic field is accompanied by the appearance of an electric field. Electromagnetic field propagates at the speed of light, i.e. 300,000 km/s.
Graphical representation of the magnetic field. Graphically, the magnetic field is represented by magnetic lines of force, which are drawn so that the direction of the line of force at each point of the field coincides with the direction of the field forces; magnetic field lines are always continuous and closed. The direction of the magnetic field at each point can be determined using a magnetic needle. The north pole of the arrow is always set in the direction of the field forces. The end of the permanent magnet, from which the lines of force come out (Fig. 35, a), is considered to be the north pole, and the opposite end, which includes the lines of force, is the south pole (the lines of force passing inside the magnet are not shown). The distribution of lines of force between the poles of a flat magnet can be detected using steel filings sprinkled on a sheet of paper placed on the poles (Fig. 35, b). The magnetic field in the air gap between two parallel opposite poles of a permanent magnet is characterized by a uniform distribution of magnetic lines of force (Fig. 36) (field lines passing inside the magnet are not shown).
Rice. 37. Magnetic flux penetrating the coil at perpendicular (a) and inclined (b) its positions with respect to the direction of magnetic lines of force.
For a more visual representation of the magnetic field, the lines of force are located less often or thicker. In those places where the magnetic role is stronger, the lines of force are located closer to each other, in the same place where it is weaker, further apart. The lines of force do not intersect anywhere.
In many cases, it is convenient to consider magnetic field lines as some elastic stretched threads that tend to contract and also mutually repel each other (have mutual lateral expansion). Such a mechanical representation of the lines of force makes it possible to clearly explain the emergence of electromagnetic forces during the interaction of a magnetic field and a conductor with a current, as well as two magnetic fields.
The main characteristics of a magnetic field are magnetic induction, magnetic flux, magnetic permeability and magnetic field strength.
Magnetic induction and magnetic flux. The intensity of the magnetic field, i.e., its ability to do work, is determined by a quantity called magnetic induction. The stronger the magnetic field created by a permanent magnet or electromagnet, the greater the induction it has. Magnetic induction B can be characterized by the density of magnetic lines of force, i.e., the number of lines of force passing through an area of 1 m 2 or 1 cm 2 located perpendicular to the magnetic field. Distinguish between homogeneous and inhomogeneous magnetic fields. In a uniform magnetic field, the magnetic induction at each point of the field has same value and direction. The field in the air gap between the opposite poles of a magnet or electromagnet (see Fig. 36) can be considered homogeneous at some distance from its edges. The magnetic flux Ф passing through any surface is determined by the total number of magnetic lines of force penetrating this surface, for example, coil 1 (Fig. 37, a), therefore, in a uniform magnetic field
F = BS (40)
where S is the cross-sectional area of the surface through which the magnetic lines of force pass. It follows that in such a field the magnetic induction is equal to the flux divided by the cross-sectional area S:
B = F/S (41)
If any surface is inclined with respect to the direction of the magnetic field lines (Fig. 37, b), then the flux penetrating it will be less than when it is perpendicular, i.e. Ф 2 will be less than Ф 1.
In the SI system of units, magnetic flux is measured in webers (Wb), this unit has the dimension V * s (volt-second). Magnetic induction in the SI system of units is measured in teslas (T); 1 T \u003d 1 Wb / m 2.
Magnetic permeability. Magnetic induction depends not only on the strength of the current passing through a straight conductor or coil, but also on the properties of the medium in which the magnetic field is created. The quantity characterizing the magnetic properties of the medium is the absolute magnetic permeability? a. Its unit is the henry per meter (1 H/m = 1 Ohm*s/m).
In a medium with greater magnetic permeability, an electric current of a certain strength creates a magnetic field with greater induction. It has been established that the magnetic permeability of air and all substances, with the exception of ferromagnetic materials (see § 18), has approximately the same value as the magnetic permeability of vacuum. The absolute magnetic permeability of vacuum is called the magnetic constant, ? o \u003d 4? * 10 -7 Gn / m. The magnetic permeability of ferromagnetic materials is thousands and even tens of thousands of times greater than the magnetic permeability of non-ferromagnetic substances. Permeability ratio? and any substance to the magnetic permeability of vacuum? o is called the relative magnetic permeability:? = ? a /? about (42)
Magnetic field strength. The intensity And does not depend on the magnetic properties of the medium, but takes into account the influence of the current strength and the shape of the conductors on the intensity of the magnetic field at a given point in space. Magnetic induction and intensity are related by the relation
H=B/? a = b/(?? o) (43)
Consequently, in a medium with a constant magnetic permeability, the magnetic field induction is proportional to its intensity.
TOPIC: MAGNETIC FIELD, ITS GRAPHIC DESCRIPTION.
Magnetic field strength is measured in amperes per meter (A/m) or amperes per centimeter (A/cm).HOMOGENEOUS AND NON-HOMOGENEOUS MAGNETIC FIELD.
Lesson - study new topic.
OBJECTIVES: to repeat - the concept of a magnetic field, how a magnetic field is created and how it can be
discover; the essence of Ampère's hypothesis - the properties of permanent magnets are explained
molecular currents.
To be able to depict graphically the lines of force of the magnetic field; know that everyone
Magnet two poles; know the nature of their interaction; know that thanks to the magnetic
The field interacts with magnetized bodies; have an idea of uniformity and
inhomogeneous magnetic field.
Develop - an idea of how the Earth's magnetic field affects living
creatures; concept of human magnetic field.
Cultivate the skills of mental operations: analysis, generalization, systematization
Knowledge gained; organize your study; use additional
Literature; conduct a physical experiment.
EQUIPMENT: magnets, magnetic needles, solenoid, projector,
ON THE BOARD: TOPIC OF THE LESSON. LESSON QUESTIONS: called a magnetic field,
“I think - so I am MAGNET-
exist." Descartes the loving stone.
As a result of which it is formed, in what
Ampère's conjecture concludes, as graphically
Represent the magnetic field, and also introduce
The concept of homogeneous and heterogeneous
magnetic field..
DURING THE CLASSES.
A. Organizational moment.
Teacher draws attention to the epigraph of the lesson: "I think - therefore I exist." Descartes
Let's guys together today we will reflect on the issues of the topic and we will be together
Exist.
B. Exploring a New Topic
1Today we are starting to study a new topic that will provide answers to questions related to the work of industrial and household appliances with natural phenomena.
You will name the TOPIC of the lesson by listening to the following legend.
The TEACHER tells the LEGEND: “in the old days they told that there is Mount Magnit at the end of the world. She stands by the sea. Trouble for a ship that sails too close. The mountain attracts iron, so much so that it pulls nails out of the boards. Ships fall apart and sink)
Question: What is the reason for this phenomenon? Answer: Because the mountain is magnetic, then near it
There is a magnetic field that
Works on metal objects.
Question: Therefore, about what? Answer: about the magnetic field.
Are we going to talk today?
The topic of the lesson is “MAGNETIC FIELD, ITS GRAPHIC IMAGE.
HOMOGENEOUS AND NON-HOMOGENEOUS MAGNETIC FIELD.»
(children write the topic of the lesson in their notebooks).
2 Today we have to remember: what is called a magnetic field, as a result of which it is formed, what is Ampère's hypothesis, how the magnetic field is graphically represented, and we will also introduce the concept of a homogeneous and inhomogeneous magnetic field.
T. Magnetic phenomena were discovered a very long time ago, let's take an excursion into history
Message-historical background prepared by students. (3-4 min)
TEACHER. As you can see, for centuries mankind has been studying magnetic phenomena.
Question: FOR WHAT, WHY STUDY MAGNETIC FIELDS.
Video clip. (questions for the film are on the tables)
Questions for fragment number 1.
In what areas are magnetic phenomena used?
Which devices work based on magnetic phenomena?
TEACHER. We studied magnetic phenomena
Magnetic field STUDENTS.
Let's remember.1 What is called a magnetic field? A special kind of matter
2. As a result of which the magnetic field The magnetic field around the constant magnetic
exists around permanent magnets? tov exists because
We conduct the experiment "Soaring Magnet".
Take two identical ring magnets,
Put one of them on the bottom of the corresponding
Size glass vessel(from the kit
electrolysis). Lower the second magnet so that
The magnets were facing each other
Same poles. Watching
“hovering” of the upper magnet over the lower one.
3. What generates a magnetic field? The magnetic field is generated by moving
Charges in a conductor. (student conducts
Oersted's experience or experience is demonstrated on
screen).
You see that the magnetic field is generated
Could there be a reverse effect?
Does a magnetic field affect charges? If a
It works, how? Yes, it works. An experience with an oscilloscope.
Get
On the oscilloscope screen, a bright, glowing
Spot. Bring an arcuate magnet to it,
Pay attention to the displacement of moving
charges under the action of a magnetic field.
Conclusion: magnetic field acts on charged particles.
Under we summarize all that has been said CONCLUSION: a magnetic field is created around any electric current and acts only on moving charges, which is hallmark magnetic field.
3 We're talking about a magnetic field, You can, with the help of iron filings.
Whether to see him and how ? Experience (student shows) or on a video disc
experience: field of magnets.
( The student explains the experience with the instruments:
Permanent magnet and metal filings.)
VIDEO FRAGMENT No. 2.
QUESTIONS TO VIDEO fragment №2.
1. What is called magnetic lines?
2. What does the direction of the magnetic lines indicate?
3 How does the influence of a magnetic field depend on distance?
We found out that the magnetic field is characterized by magnetic lines.
WHAT TYPES OF MAGNETIC FIELD EXIST?
Consider a bar magnet and its magnetic lines.
QUESTION. What can be said about the density of lines AND ABOUT THE FORCE OF THE MAGNETIC FIELD ACTING ON THE POINTS IN WHICH THE MAGNETIC ARROWS ARE LOCATED? GIVE A NAME TO THIS TYPE OF MAGNETIC FIELD.
Answer: the closer to the magnet, the thicker the lines,
operating at the points where they are located
magnetic arrows are different. Such
the field is said to be inhomogeneous.
Teacher - Let's read this definition again. (the student reads on the slide, everyone makes an insert in notebooks, and next to them they write down the definition of the magnetic field).
Now pay attention to the internal fields of the permanent magnet and the solenoid.
What can you say about them?
Answer: Because lines are located with the same
Density and have one direction,
This field is homogeneous.
Formulate the definition of a homogeneous field. Students define homogeneous
Conclusion: 1. What types of magnetic field have we met?
2. Is the Earth's magnetic field homogeneous or non-uniform?
STUDENTS: 1. We got acquainted with two types of magnetic field
Homogeneous and heterogeneous.
2. Is the Earth's magnetic field non-uniform?
Listen to student messages. How does a change in the Earth's magnetic field affect living things?
Organisms?
To summarize what has been said: in the lesson we talked about magnetic phenomena: what is called a magnetic field? what causes it to form? What is Ampère's hypothesis? How is a magnetic field represented graphically? and also introduced the concept of a homogeneous and inhomogeneous magnetic field.
Make a conclusion: WHY, WHY STUDY MAGNETIC FIELDS.
The children draw their own conclusions.
D.Z. §43-44. Ex. 34 (1.2) Answers to questions after §. Individual tasks:
YOU THOUGHT WELL TODAY, THIS MEANS WE REALLY EXISTED. THANKS.
GRADING
Thanks for the lesson. goodbye
Questions for students in class.
Question to the class: WHY, WHY STUDY MAGNETIC FIELDS
Questions for fragment number 1.
1. In what areas are magnetic phenomena used?
2. The operation of which devices is based on magnetic phenomena?
Questions for fragment number 2.
3. How is the magnetic field graphically depicted?
4. What are called magnetic lines?
5. What does the direction of the magnetic lines indicate?
6.Where do the magnetic field lines start and where do they end?
QUESTIONS FOR CONSOLIDATION.
1. Movements repeating at certain intervals ...
2. A field whose magnetic lines are of the same density is called………
3. The imaginary lines along which the magnetic needles are located are called……..
4. The magnetic field has north and south…….
5. A scientist who proved that the magnetic field around a permanent magnet is formed as a result of the rotation of charged particles in one direction.
6. A cylindrical wire coil with current is called - ... ...
: 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. Develop cognitive activity 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.
- educational
- 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.
- Receipt scientific fact about the relationship between the direction of the lines of the magnetic field of the current with the direction of the current in the conductor and in the solenoid.
- Application of the gimlet rule to determine the direction of magnetic field lines in the direction of current.
- Application of the rule right hand to determine the direction of the magnetic field lines in the direction of the current.
- Application of the right hand rule to determine the direction of the magnetic field lines in the direction of the current in the solenoid.
- Solution of practical problems.
- Summarizing.
- Homework.
- Students will understand the meaning of the terms: “non-uniform and uniform magnetic field”, “magnetic lines of non-uniform and uniform magnetic fields”.
- Schoolchildren are aware of the relationship between the direction of the lines of the magnetic field of the current with the direction of the current in the conductor and in the solenoid.
- Students will be able to solve practical problems:
- Around motionless charges exist ... field.
- Around mobile charges….
- With a magnetic needle.
- According to the gimlet's rule.
- Right hand rule.
- Magnetic lines are closed curves, so the magnetic field is called vortex. This means that there are no magnetic charges in nature.
- The denser the magnetic lines are, the stronger the magnetic field.
- If the magnetic lines are parallel to each other with the same density, then such a magnetic field is called uniform.
- If the magnetic lines are curved, this means that the force acting on the magnetic needle at different points of the magnetic field is different. Such a magnetic field is called non-uniform.
- Task for the first person: draw the magnetic field of a straight conductor with current.
- Task for the second person: draw the magnetic field of the solenoid.
- Task for the third person: draw the magnetic field of a permanent magnet.
- On fig. 88 shows a section BC of a current-carrying conductor. Around it, in one of the planes, the lines of the magnetic field created by this current are shown. Is there a magnetic field at point A?
- On fig. 88 shows three points: A, M, N. In which of them will the magnetic field of the current flowing through the conductor BC act on the magnetic needle with the greatest force? with the least force?
- Peryshkin A.V., Gutnik E.M. Textbook for educational institutions "Physics-9", 12th edition. – M.: Bustard, 2009.
- Gromov S.V.. "Physics-9": Textbook for educational institutions. 3rd ed. - M .: Education, 2002.
- Pinsky A.A., Razumovsky V.G. Textbook for educational institutions "Physics-8". M.: Education, 2003.
- “Fundamentals of methods of teaching physics. General questions” edited by L.I. Reznikova, A.V. Peryshkina, P.A. Znamensky. - M .: Education, 1965.
- Scientific and methodological journal "Physics at School", Publishing House "School-Press", 1999, 6.
- Journal "Physics at school". - 2003. - 7. - p.30.
- Dubinin E.M., Podgorny I.M. The magnetic field of celestial bodies. – M.: Knowledge, 1998.
- “Fundamentals of methods of teaching physics. General questions” / edited by L.I. Reznikova, A.V. Peryshkina, P.A. Znamensky - "Enlightenment", Moscow, 1965.
- Gromov S.V., Rodina N.A. Physics-9: Textbook for educational institutions - 3rd ed. - M .: Education, 2002.
- Lukashik V.I. Collection of questions and problems in physics. 7–9 cells - M.: Enlightenment, 2002. - 192p.
- Maron A.E., Maron E.A. Control texts in physics. 7–9 cells - M.: Enlightenment, 2002. - 79p.
today I found out...
it was interesting…
it was difficult…
I did assignments...
I realized that...
Now I can…
I felt that...
I purchased...
I learned…
I managed …
Tasks:
: 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.
Equipment. interactive board, a device for demonstrating the location of iron filings around a straight conductor with current, a device for demonstrating the location of iron filings around a solenoid, a power source, a 220 W coil, bar magnets, horseshoe magnets, magnetic needles, copper wire, iron filings, magnets, compass. Presentation ( Attachment 1).Additional material ( Annex 2).
Type of lesson: lesson learning new material.
Lesson type: research lesson.
During the classes
1. Organizational stage
The stage of updating knowledge and actions.
2. Motivational stage
Educational outcomes to be achieved by students:
- to determine the direction of the lines of the magnetic field of the current in the direction of the current in the conductor;
- to determine the direction of the lines of the magnetic field of the current in the direction of the current in the solenoid;
- in the direction of the current in the conductor, determine the direction of the magnetic lines of the magnetic field of the current;
– to determine the direction of the magnetic lines of the magnetic field of the current by the direction of the current in the solenoid.
1. The stage of updating knowledge and actions
Magnetism has been known since the fifth century BC, but the study of its essence has progressed very slowly. The properties of a magnet were first described in 1269. In the same year, the concept of a magnetic pole was introduced. The word “magnet” (from the Greek magnetis eitos. A mineral consisting of - FeO (31%) Fe 2 O 3 (69%)) means the name of the ore mined in the area of Magnesia (now it is the city of Manisa in Turkey). The magnet is the "stone of Hercules", the "loving stone", the "wise iron", and the "royal stone".
Slide 1. The origin of the word is a magnet.
This name was coined by the ancient Greek playwright Euripides (in the 5th century BC) Rich deposits magnetic iron ore are available in the Urals, Ukraine, Karelia and the Kursk region. At present, it has been possible to create artificial magnets that have greater magnetic properties than natural ones. The material for them are alloys based on iron, nickel, cobalt and some other metals.
Slide 2. Artificial magnets.
A magnet has a different attraction force in different areas, and this force is most noticeable at the poles. You already know that there is a magnetic field around any magnet. This field attracts the iron to the magnet.
Slide 3. Different attractive force of magnets on the poles.
The outer, molten, core of the Earth is in constant motion. As a result of this, magnetic fields arise in it, which ultimately form the Earth's magnetic field.
slide 4. Earth- big magnet
Previously, you studied the various effects of electric current, in particular, the magnetic effect. It manifests itself in the fact that interaction forces arise between conductors with current, which are called magnetic. The first experiments to detect a magnetic field around a conductor with current were carried out by Hans Christian Oersted in 1820.
Slide 5. Experience of Hans Christian Oersted in 1820.
Slide 6. Scheme of the experience of Hans Christian Oersted in 1820.
His unexpected and simple experiments with the deflection of a magnetic needle near a current-carrying conductor have been tested by a number of scientists. This test also brought new results, which formed the experimental basis of the first theory of magnetism. He first suggested a possible connection between electric current and magnetism, and was recorded in 1735 in one of the scientific London journals. However, the solution came only when researchers learned how to receive an electric current .
Consider a series of experiments. Experience in detecting the magnetic field of the current. We will assemble the electrical circuit according to the scheme. We place a magnetic arrow near the conductor. Let's answer the question: "How do a current-carrying conductor and a magnetic needle interact if the circuit is not closed?".
Slide 7. Experience in detecting the magnetic field of the current.
Let's answer the question: "How do a current-carrying conductor and a magnetic needle interact if the circuit is closed?".
Slide 8. Experience in detecting a magnetic field of current.
Let's answer the question: "How do a current-carrying conductor and a magnetic needle interact when the circuit is opened?".
Slide 9. Experience in detecting the magnetic field of the current.
Experiments suggested the existence of a magnetic field around a current-carrying conductor. It can be seen from experiments that a magnetic needle, which can freely rotate around its axis, is always installed, orienting itself in a certain way, in a given region of the magnetic field. Based on this, the concept of the direction of the magnetic field at a given point is introduced.
Iron filings are attracted to a permanent magnet. Based on the available knowledge, we assert that this is due to the magnetic field that arises around the permanent magnets.
Slide 10. Experience. Iron filings are attracted to a permanent magnet.
We conclude that the source of the magnetic field are:
a) moving electric charges;
b) permanent magnets.
Slide 11. Sources of the magnetic field.
Using iron filings, we demonstrate the spectrum of the direct current magnetic field at a given point.
Slide 12. The location of metal filings around a straight conductor with current.
Let's answer the question: "How can a magnetic field be detected?".
a) with iron filings. Getting into a magnetic field, iron filings are magnetized and are located along magnetic lines.
b) acting on a current-carrying conductor. Getting into a magnetic field conductor with current starts to move, because a force acts on it from the side of the magnetic field.
Slide 13. Magnetic field detection options.
Let us determine, on the basis of existing knowledge, the causes of the magnetic field.
We affirm that the magnetic field is generated by permanent magnets and moving electric charges and is detected by the action on moving electric charges. The magnetic field weakens with distance from the source.
Slide 14. Magnetic field and its causes. Let's draw conclusions:
There is a magnetic field around a conductor with current (i.e. around moving charges). It acts on the magnetic needle, deflecting it.
Electric current and magnetic field are inseparable from each other.
We will answer questions:
slide 15. Conclusions.
2. Motivation for new learning material
Graphical representation of the magnetic field. All magnets have two kinds of poles. These poles are called southern (S) and northern (N).
Slide 16. Poles of magnets.
An idea of the magnetic field can be obtained using modern methods. But this can be done with the help of iron filings.
Slide 17. Magnetic field lines.
In order to get the appearance of the magnetic field of a permanent magnet, you need to do the following: put a sheet of cardboard on a bar magnet, and evenly sprinkle it with iron filings. Without moving the magnet and cardboard sheet relative to each other, gently tap the sheet so that the sawdust can be freely redistributed. Watch how sawdust lines up on cardboard.
Slide 18. Lines of force of the magnetic field of a strip magnet ..
The magnetic field lines are closed lines. Outside, magnetic lines of force exit the north pole of the magnet and enter the south pole, closing inside the magnet.
The lines formed by magnetic needles or iron filings in a magnetic field came to be called magnetic field lines.
Slide 19. Graphical representation of the magnetic field of the current.
The lines along which the axes of small magnetic arrows are located in a magnetic field are called magnetic field lines
.
The magnetic lines of the current magnetic field are closed curves
enclosing the conductor.
The direction that points North Pole
magnetic needle at each point of the field, taken as the direction of the magnetic lines of the magnetic field.
3. Understanding new learning material
We continue to explore the world. The topic of today's lesson is “Magnetic field and its graphical representation. Inhomogeneous and uniform magnetic field. Dependence of the direction of magnetic lines on the direction of current in the conductor”.
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. A magnetic field also arises when the current passes through an electrolyte solution, where charge carriers are positively and negatively charged ions moving towards each other.
Since electric current is the directed movement of charged particles, we can say that the magnetic field is created by moving charged particles, both positive and negative. Recall that, according to the Ampère hypothesis, ring currents arise in atoms and molecules of matter as a result of the movement of electrons. In magnets, these elementary ring currents are oriented in the same way. Therefore, the magnetic fields formed around each such current have the same directions. These fields reinforce each other, creating a field in and around the magnet.
Slide 20. The direction of the magnetic line at point B
For a visual representation of the magnetic field, we used magnetic lines (they are also called magnetic field lines). Recall that magnetic lines– these are imaginary lines along which small magnetic needles placed in a magnetic field would be located. The direction of the magnetic line is conventionally taken as the direction that indicates the north pole of the magnetic needle, placed at this point.
Slide 21. Magnetic lines are closed.
Slide 22. The magnetic field of the coil and the permanent magnet.
A coil with current, like a magnetic needle, has 2 poles - north and south.
The magnetic effect of the coil is stronger, the more turns in it.
As the current increases, the magnetic field of the coil increases.
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 23. Magnetic lines of a straight conductor with current. Slide 24. Consider the magnetic lines of the solenoid.
Inhomogeneous and uniform magnetic field.
Consider the pattern of magnetic field lines of a permanent bar magnet shown in the figure.
Slide 25. Representation of the magnetic field using magnetic lines.
From the 8th grade physics course, we know that magnetic lines come out of the north pole of the magnet and enter the south. Inside the magnet, they are directed from the south pole to the north. Magnetic lines have neither beginning nor end: they are either closed or, as middle line in the figure, go from infinity to infinity. Outside the magnet, the lines are densest at its poles. This means that the field is strongest near the poles, and as it moves away from the poles, it weakens. The closer the magnetic needle is to the pole of the magnet, the more force the magnet field acts on it. Since the magnetic lines are curved, the direction of the force with which the field acts on the arrow 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 of the field, can be different both in absolute value and in direction. Such a field is called inhomogeneous.
The lines of an inhomogeneous magnetic field are curved, and their density varies from point to point.
Properties of magnetic lines: if the magnetic lines are curved and located with unequal density, then the magnetic field is non-uniform.
Slide 26. Properties of magnetic lines.
In a certain limited region of space, it is possible to create a uniform magnetic field, i.e., a field, at any point of which the force of action on the magnetic needle is the same in magnitude and direction. The magnetic 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.
Slide 27. Properties of magnetic lines.
Slide 28. Uniform and non-uniform magnetic fields.
What you need to know about magnetic lines?
Slide 29. What you need to know about magnetic lines?
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, and if they are towards us because of the drawing, then with dots. As in the case of the current, each cross is, as it were, the tail of an arrow flying from us, and the dot 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).
Slide 30. Image of a uniform magnetic field.
There are several ways to determine the direction of magnetic lines.
Slide 31. Determining the direction of magnetic lines.
The first rule of the right hand: if you clasp the conductor with the palm of your right hand, directing the thumb along the current, then the remaining fingers of this hand will indicate the direction of the magnetic field lines of this current.
Slide 32. The first rule of the right hand.
The second rule of the right hand: if you clasp the solenoid with the palm of your right hand, pointing four fingers along the current in the turns, then the left thumb will indicate the direction of the magnetic lines inside the solenoid.
Slide 33. The second rule of the right hand.
If you place a frame with a current at a certain point of the magnetic field, then the magnetic field will have an orienting effect on it - the frame will be installed in the magnetic field in a certain way. Now you need to draw a normal to the frame. The direction of the normal can be used to determine the direction of the magnetic induction vector at this point of the magnetic field.
Gimlet rule: if the gimlet handle is rotated in the direction of the current in the frame, then the direction of the gimlet will show the direction of the magnetic induction vector at a given point in the field.
Slide 34. The gimlet rule.
Solution of practical problems.
Slide 35. Which statements are true?
Slide 36. Finish the phrase: “There is a current around a conductor ...
a) magnetic field.
b) Electric field.
c) Electric and magnetic fields.
slide 37. What you need to know about magnetic lines?
Slide 38. What does the north pole of a magnetic needle point to? What are magnetic lines?
Slide 40. At what point is the magnetic field the strongest?
Slide 41. Determine the direction of the current according to the known direction of the magnetic lines.
Slide 42. Answer. Determining the direction of the current according to the known direction of the magnetic lines.
Slide 43. Which of the options corresponds to the arrangement of magnetic lines around a rectilinear current-carrying conductor located perpendicular to the plane of the picture?
Slide 44. Which of the options corresponds to the arrangement of magnetic lines around a straight current-carrying conductor located vertically?
Slide 45. Which of the options corresponds to the layout of the magnetic lines around the solenoid?
Slide 46. What are the magnetic lines of a solenoid?
4. Awareness of educational material
Questions: Slide 47.
1. Which statements are true?
a) There are electric charges in nature.
B) There are magnetic charges in nature.
C) There are no electric charges in nature.
D) There are no magnetic charges in nature.a) A and B, b) A and C, c) A and D, d) B, C and D.
2. What generates a magnetic field?
3. What creates the magnetic field of a permanent magnet?
4. What are magnetic lines?
5. What can be judged from the pattern of magnetic field lines?
6. What kind of magnetic field - homogeneous or inhomogeneous - is formed around a bar magnet? around a straight current-carrying conductor? inside a solenoid whose length is much greater than its diameter?
Slide 49. Pictures of magnetic fields.
The work of students at the blackboard.
Exercise 33
5. Summary of the lesson
6. Homework
§§43–45. Ex. 33, 34, 35.
Literature
11B students Alekseev Alexander and Barbashov Andrey
Presentation for the lesson on summarizing the material on the topic "Magnetic field".
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Presentation for a physics lesson on the topic Magnetic field and its graphic representation. Completed by students of class 11 "B" Alekseev Alexander Barbashov Andrey 2013
Theory electromagnetic field According to Maxwell's theory, alternating electric and magnetic fields cannot exist separately: a changing magnetic field generates an electric field, and a changing electric field generates a magnetic one.
Magnetic field - a force field acting on moving electric charges and on bodies with a magnetic moment, regardless of the state of their movement, the magnetic component of the electromagnetic field. The magnetic field can be created by the current of charged particles and / or magnetic moments of electrons in atoms (and magnetic moments of other particles , although to a much lesser extent) (permanent magnets). In addition, it appears in the presence of a time-varying electric field. The main power characteristic of the magnetic field is the magnetic induction vector (magnetic field induction vector). From a mathematical point of view, it is a vector field that defines and specifies the physical concept of a magnetic field. Often the vector of magnetic induction is called simply a magnetic field for brevity (although this is probably not the most strict use of the term).
Is it true that at a given point in space there is only an electric or only a magnetic field? A charge at rest creates an electric field. But the charge is at rest only with respect to a certain frame of reference. Relative to others, it can move and, therefore, create a magnetic field. A magnet lying on a table creates only a magnetic field. But an observer moving relative to it will also detect an electric field
The statement that at a given point in space there is only an electric or only a magnetic field is meaningless, if you do not specify in relation to which frame of reference these fields are considered. Conclusion: electric and magnetic fields are a manifestation of a single whole: the electromagnetic field. The source of the electromagnetic field are rapidly moving electric charges.
Permanent magnets N - magnet north pole S - South Pole Magnet 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
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
Opposite magnetic poles attract, like poles repel. The interaction of magnets is explained by the fact that any magnet has a magnetic field, and these magnetic fields interact with each other.
Hypothesis of Ampère + e - S N 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 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 A magnetic field is a component of an 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.
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.
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
Where does an inhomogeneous magnetic field exist? around a bar magnet around a solenoid (coil with current).
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.
Where does a uniform magnetic field exist? Inside the bar magnet and inside the solenoid, if its length is much greater than the diameter
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 near the equator
If the sun is powerful flash, the solar wind increases. 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 tremendous speeds. It is interesting
The result of the interaction of the solar wind with the Earth's magnetic field is the aurora. Invading earth's atmosphere, particles of the solar wind (mainly electrons and protons) are guided by the magnetic field and focused in a certain way. Colliding with atoms and molecules atmospheric air, they ionize and excite them, resulting in a glow, which is called the aurora. It is interesting
Influence study various factors weather conditions a special discipline, biometrology, deals with the body of a healthy and sick person. Magnetic storms bring discord into the work of the cardiovascular, respiratory and nervous system, and also change the viscosity of the blood; in patients with atherosclerosis and thrombophlebitis, it becomes thicker and coagulates faster, and in healthy people, on the contrary, increases. It is interesting
What bodies are called permanent magnets? What generates the magnetic field of a permanent magnet? What is called magnetic poles magnet? How do homogeneous magnetic fields differ from non-uniform ones? How do the poles of magnets interact with each other? Explain why the needle attracts the paperclip? (see pic) Fastening
Thank you for your work and attention!