Src="http://present5.com/presentation/3/46060323_437197076.pdf-img/46060323_437197076.pdf-1.jpg" alt="(!LANG:> Magnetic field and its graphic image Inhomogeneous and homogeneous "> Magnetic field and its graphical representation Inhomogeneous and uniform magnetic field Gimlet rule Rule right hand left hand rule

Src="http://present5.com/presentation/3/46060323_437197076.pdf-img/46060323_437197076.pdf-2.jpg" alt="(!LANG:>Magnetic field and its graphic representation For visual presentation"> 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="http://present5.com/presentation/3/46060323_437197076.pdf-img/46060323_437197076.pdf-3.jpg" alt="(!LANG:>Inhomogeneous and uniform magnetic field The force with which the field of a bar 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="http://present5.com/presentation/3/46060323_437197076.pdf-img/46060323_437197076.pdf-4.jpg" alt="(!LANG:>Gimlet Rule"> 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 gimlet rule. The rule of the gimlet is as follows: if the direction of the translational movement of the gimlet coincides with the direction of the current in the conductor, then the direction of rotation of the gimlet handle coincides with the direction of the lines of the magnetic field of the current. Using the gimlet 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="http://present5.com/presentation/3/46060323_437197076.pdf-img/46060323_437197076.pdf-5.jpg" alt="(!LANG:>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="http://present5.com/presentation/3/46060323_437197076.pdf-img/46060323_437197076.pdf-6.jpg" alt="(!LANG:>Right hand rule for conductor with current If 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!}

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, to get a picture of the lines of force of the magnetic field of a permanent magnet, solenoid, conductor through which flows electricity. Systematize knowledge on the main issues of the topic “Electromagnetic field”, continue to teach how to solve qualitative and experimental problems.

Educational : activate cognitive activity students in physics classes. 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.

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 overcome great distances, fearing the winter cold, and in the spring they return back. 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".

Graphical representation of the magnetic field. Magnetic induction vector flux

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

Studies have shown that the lines of magnetic induction are closed lines covering currents. The density of the lines of magnetic induction is proportional to the magnitude of the vector at a given location in the field. In the case of a direct current magnetic field, 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 gimlet rule. In the case of a direct current magnetic field, the gimlet must be rotated in such a way that its translational movement coincides with the direction of the current in the wire, then the rotational movement of the gimlet handle coincides with the direction of the magnetic induction lines (Fig. 7).

On fig. 8 and 9 show the patterns of the lines of magnetic induction of the circular current field and the field of the solenoid. The 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 ( = const). The field of a solenoid 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 penetrating a certain surface is called the magnetic flux through this surface. Designate the magnetic flux with the letter F in (or F).

,

(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 webers (Wb): [F] = [B] × [S] = Tl × m 2 = =

We know that a conductor with current creates a magnetic field around itself. A permanent magnet also creates a magnetic field. Will the fields they create be different? Undoubtedly, they will. The difference between them can be seen clearly if you create graphic 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 current-carrying conductor and the magnetic field formed by it in section, we will see a set of circles of different diameters. The figure on the left shows just a conductor with current.

The action of the magnetic field will be the stronger, the closer to the conductor. As you move away from the conductor, the action and, accordingly, the strength of the magnetic field will decrease.

When permanent magnet we have lines coming out of the south pole of the magnet, passing along the body of the magnet itself and entering its north pole.

Having sketched such a magnet and the magnetic lines of the magnetic field formed by it graphically, we will see that the effect of the magnetic field will be strongest near the poles, where the magnetic lines are most densely located. The drawing 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 current. The magnetic lines will have the greatest intensity at the two ends or ends of the coil. In all the above cases, we had a non-uniform magnetic field. The magnetic lines had 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 arranged in parallel and have the same density in only 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” inside 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 number of technological processes, so it is possible to design solenoids of sufficient size so that the necessary processes can be carried out 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 in such a way that these lines are directed towards us or in the opposite direction from us? Then they are drawn in the form of a dot 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 moving away from us.