Src \u003d "http://present5.com/presentation/3/46060323_437197076.pdf-img/46060323_437197076.pdf-1.jpg" alt \u003d "(! LANG:\u003e The magnetic field and its graphic image Inhomogeneous and homogeneous "\u003e Magnetic field and its graphic representation Inhomogeneous and homogeneous magnetic field Rule of thumb Rule right hand Left hand rule

Src \u003d "http://present5.com/presentation/3/46060323_437197076.pdf-img/46060323_437197076.pdf-2.jpg" alt \u003d "(! LANG:\u003e Magnetic field and its graphical representation For visualization"> Магнитное поле и его графическое изображение Для наглядного представления магнитного поля мы пользовались магнитными линиями. Магнитные линии – это воображаемые линии, вдоль которых расположились бы маленькие магнитные стрелки, помещенные в магнитное поле. На рисунке показано магнитная линия (как прямолинейная, так и криволинейная). По картине магнитных линий можно судить не только о направлении, но и о величине магнитного поля.!}

Src \u003d "http://present5.com/presentation/3/46060323_437197076.pdf-img/46060323_437197076.pdf-3.jpg" alt \u003d "(! LANG:\u003e Inhomogeneous and uniform magnetic field The force with which the field of a strip magnet"> Неоднородное и однородное магнитное поле Сила, с которой поле полосового магнита действует на помещенную в это поле магнитную стрелку, в разных точках поля может быть различной как по модулю, так и по направлению. Такое поле называют неоднородным. Линии неоднородного магнитного поля искривлены, их густота меняется от точки к точке. В некоторой ограниченной области пространства можно создать однородное магнитное поле, т. е. поле, в любой точке которого сила действия на магнитную стрелку одинакова по модулю и направлению. Для изображения магнитного поля пользуются следующим приемом. Если линии однородного магнитного поля расположены перпендикулярно к плоскости чертежа и наплавлены от нас за чертеж, то их изображают крестиками, а если из-за чертежа к нам – то точками.!}

Src \u003d "http://present5.com/presentation/3/46060323_437197076.pdf-img/46060323_437197076.pdf-4.jpg" alt \u003d "(! LANG:\u003e Gimbal rule It is known that the direction of the current magnetic field lines is related to"> Правило буравчика Известно, что направление линий магнитного поля тока связано с направлением тока в проводнике. Эта связь может быть выражена !} simple rule, which is called the gimbal rule. The gimbal's rule is as follows: if the direction of the gimbal's translational motion coincides with the direction of the current in the conductor, then the direction of rotation of the gimbal handle coincides with the direction of the current magnetic field lines. Using the gimbal rule in the direction of the current, you can determine the directions of the lines of the magnetic field created by this current, and in the direction of the lines of the magnetic field - the direction of the current that creates this field.

Src \u003d "http://present5.com/presentation/3/46060323_437197076.pdf-img/46060323_437197076.pdf-5.jpg" alt \u003d "(! LANG:\u003e Right hand rule It is more convenient to determine the direction of the solenoid magnetic field lines"> Правило правой руки Для определения направления линий магнитного поля соленоида удобнее пользоваться другим правилом, которое иногда называют правилом правой руки: если обхватить соленоид ладонью правой руки, направив четыре пальца по направлению тока в витках, то отставленный большой палец покажет направление линий магнитного поля внутри соленоида. Соленоид, как и магнит, имеет полосы: тот конец соленоида, из которого магнитные линии выходят, называется северным полюсом, а тот, в который входят, - южным. Зная направления тока в соленоиде, по правилу правой руки можно определить направление магнитных линий внутри него, а значит, и его магнитные полюсы и наоборот. Правило правой руки можно применять и для определения направления линий магнитного поля в центре одиночного витка с током.!}

Src \u003d "http://present5.com/presentation/3/46060323_437197076.pdf-img/46060323_437197076.pdf-6.jpg" alt \u003d "(! LANG:\u003e Right hand rule for a conductor with current If the right hand"> Правило правой руки для проводника с током Если правую руку расположить так, чтобы большой палец был направлен по току, то остальные четыре пальца покажут направление линии магнитной индукции!}

Lesson outline plan number 16.

Lesson topic: “Magnetic field and its graphic representation. Inhomogeneous and uniform magnetic field "

Objectives:

Educational : 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 non-uniform and homogeneous magnetic fields. In practice, to obtain a picture of the lines of force of the magnetic field of a permanent magnet, a solenoid, a conductor through which flows electricity... To systematize knowledge on the main issues of the topic "Electromagnetic field", to continue teaching to solve qualitative and experimental problems.

Developing : activate cognitive activity students in physics lessons. Develop cognitive activity students.

Educational : to contribute to the formation of the idea of \u200b\u200bthe cognizability of the world. To cultivate hard work, mutual understanding between students and the teacher.

Tasks:

Educational : deepening and expanding knowledge about the magnetic field, substantiate the connection between the direction of the magnetic lines of the current magnetic field 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 there are no causeless phenomena, that experience is a criterion for the truth of knowledge.

Developing : continue to work on the formation of skills to analyze and generalize knowledge about the magnetic field and its characteristics. Engaging students in active practical activities when doing experiments.

Equipment: presentation,table, projector, screen, magnite 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 minutes)

1. Organizational moment.

We got up and leveled ourselves. Hello, sit down.

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 overcome great distances, fearing winter cold, and in the spring they come back. Birds are guided by the earth's magnetic field. So this is it 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. Learning a new topic.

The history of the magnet is over two and a half thousand years old.

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 was called 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 connected directly with the activity of the Gods.

This is how the ancient Greek sage Socrates described the property of this stone: “This stone not only attracts the iron ring, it also 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 how are the properties of magnets determined? For this, let's see 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 with opposite poles?

Why are pieces, iron filings attracted to the magnet? Just as a glass rod attracts pieces of paper to itself, similarly a magnet attracts iron filings to itself 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 directionally along the conductor.

Since electric current is the directed movement of charged particles, we can say thata magnetic field is created by moving charged particles, both positive and negative.

So let's write the definition:

A magnetic field is a special type of matter that is created around magnets by moving charged particles, both positive and negative.

Slide 5

Remember that if the particles move, a magnetic field is created. We said that the MP is a special type of matter, it is called a special type, because not perceived by the senses.

For detecting m. magnetic arrows are used.

To visualize the magnetic field, we use magnetic lines (also called magnetic field lines). Recall thatmagnetic lines - these are imaginary lines along which small magnetic arrows would be placed in a magnetic field. Slide

A magnetic line can be drawn through any point in space in which a magnetic field exists.

In Figure 86,a, b it is shown that the magnetic line (both straight and curved) is drawn so that at any point of this line the tangent to it coincides with the axis of the magnetic arrow placed at this point... Slide 6

Magnetic lines are closed. For example, the pattern of the magnetic lines of a straight conductor with current is concentric circles lying in a plane perpendicular to the conductor.Slide 7

In those areas of space where the magnetic field is stronger, magnetic lines are depicted closer to each other, i.e., denser 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, bythe picture of magnetic lines can be judged not only about the direction, but also about the magnitude of the magnetic field (i.e., about which points in space the field acts on the magnetic needle with greater force, and at which - with less).

Let's take a look at fig. 88 in the textbook: a conductor with a VS current is depicted, let's remember what e-mail is. current - movement charged. particles, and we said that if the particles move, then a magnetic field is created. Let's take a look at the pointN will the magnetic field work? 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.

The magnetic field is of 2 types: homogeneous and non-uniform. Let's take a look at these types of magnetic fields.

Magnetic lines have no beginning or end: they are either closed or go from infinity to infinity. Figure: 89

Outside the magnet, the magnetic lines are most densely located at its poles. This means that near the poles the field is the strongest, and with distance from the poles it weakens. The closer the magnetic needle is to the pole of the magnet, the greater in magnitude the force of 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.

In this way,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 magnitude 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 an inhomogeneous magnetic field is the field around a straight conductor with current. 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. It can be seen from this figure that the magnetic lines of the field created by a straight conductor with current are concentric circles, the distance between which increases with distance from the conductor.

In some limited area of \u200b\u200bspace, you can createhomogeneous 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.

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 uniform if the length of the solenoid is much greater than its diameter (outside the solenoid the field is nonuniform, its magnetic lines are located approximately the same as for a strip magnet). From this figure we can see thatthe magnetic lines of a uniform magnetic field are parallel to each other and are located with the same density. The field inside the permanent strip magnet in its central part is also homogeneous (see Fig. 89).

Slide11

The following technique is used to display the magnetic field. 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 to us, then dots (Fig. 93). As in the case of the current, each cross is, as it were, the tail unit of an arrow flying from us, as it were, and a 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, the Earth is surrounded by a magnetic field. There is a large magnet inside the earth that 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 homing pigeons, for example, also have a semblance of a 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. Land "," M. p. in living organisms ”,“ Magnetic storms ”.

Graphical representation of the magnetic field. Flux vector of magnetic induction

The magnetic field can be represented graphically using magnetic induction lines. The line of magnetic induction is a line whose tangent at each point coincides with the direction of the magnetic induction vector (Fig. 6).

Studies have shown that lines of magnetic induction are closed lines that embrace currents. The density of the lines of magnetic induction is proportional to the magnitude of the vector at a given place of the field. In the case of a magnetic field of a forward current, the lines of magnetic induction have the form of concentric circles lying in planes perpendicular to the current, centered on a straight line with current. The direction of the lines of magnetic induction, regardless of the shape of the current, can be determined by the gimbal rule. In the case of a direct current magnetic field, the gimbal must be rotated so that its translational motion coincides with the direction of the current in the wire, then the rotational movement of the gimbal handle coincides with the direction of the magnetic induction lines (Fig. 7).

In fig. 8 and 9 show the patterns of the magnetic induction lines of the circular current field and the solenoid field. A solenoid is a collection of circular currents with a common axis.

The lines of the induction vector inside the solenoid are parallel to each other, the density of the lines is the same, the field is uniform (\u003d const). The solenoid field is similar to the field of a permanent magnet. The end of the solenoid from which the induction lines come out is similar to the north pole - N, the opposite end of the solenoid is similar to the south pole - S.

The number of lines of magnetic induction that penetrate a certain surface is called the magnetic flux through that surface. Designate the magnetic flux by the letter Ф в (or Ф).

,

(3)

Where α is the angle formed by the vector and the normal to the surface (Fig. 10).

Is the projection of the vector onto the normal to the area S.

The magnetic flux is measured in Weber (Wb): [Ф] \u003d [B] × [S] \u003d T × m 2 \u003d \u003d

We know that a conductor with a current creates a magnetic field around itself. A permanent magnet also creates a magnetic field. Will the fields they create differ? Undoubtedly they will. The difference between them can be clearly seen if you create graphical images of magnetic fields. The magnetic lines of the fields will be directed differently.

Homogeneous magnetic fields

When conductor with current magnetic lines form closed concentric circles around the conductor. If we look at a conductor with a current and the magnetic field formed by it in a section, we will see a set of circles of different diameters. The figure on the left shows just a conductor with current.

The closer to the conductor, the stronger the effect of the magnetic field. With distance from the conductor, the action and, accordingly, the strength of the magnetic field will decrease.

When permanent magnet we have lines emerging from the south pole of the magnet, passing along the very body of the magnet and entering its north pole.

Having drawn such a magnet and the magnetic lines of the magnetic field formed by it graphically, we will see that the strongest effect of the magnetic field will be near the poles, where the magnetic lines are most densely located. The picture on the left with two magnets just depicts a magnetic field. permanent magnets.

We will see a similar picture of the arrangement of magnetic lines in the case of a solenoid or a coil with a current. The magnetic lines will have the greatest intensity at the two ends or ends of the coil. In all of the above cases, we had an inhomogeneous magnetic field. The magnetic lines were in different directions, and their density was different.

Can a magnetic field be uniform?

If we look closely at the graphic representation of the solenoid, we will see that the magnetic lines are parallel and have the same density only in one place inside the solenoid.

The same picture will be observed inside the body of a permanent magnet. And if in the case of a permanent magnet we cannot "climb" into its body without destroying it, then in the case of a coil without a core or a solenoid, we get a uniform magnetic field inside them.

Such a field may be required by a person in a row technological processestherefore it is possible to design solenoids large enough to carry out the necessary processes inside them.

Graphically, we are used to depicting magnetic lines as circles or segments, that is, we seem to see them from the side or along. But what if the drawing is created so that these lines are directed at us or in the opposite direction from us? Then they are drawn in the form of a point or a cross.

If they are directed at us, then they are depicted as a point, as if it were the tip of an arrow flying at us. In the opposite case, when they are directed away from us, they are drawn in the form of a cross, as if it were the tail of an arrow receding from us.