We know from experience that magnets attract iron and other magnets. They have a magnetic field around them. When a closed conducting circuit enters this field, an electric current may occur in it, that is, the appearance of an electric field.

This phenomenon is known and is called electromagnetic induction. However, a number of questions arise. Does the resulting electric field differ from the field of stationary charges? What role does the conductor play, that is, does the electric field arise only in the conductor brought to the magnet? Or does this field exist independently of foreign objects, along with the magnetic one?

The answers to these questions were given by the English scientist James Maxwell, who created the theory of the electromagnetic field. In the ninth grade, this question is studied only in general terms, but at a sufficiently deep level to answer the above questions.

So, what does physics say about the electromagnetic field?

It has been proved theoretically and practically that a magnetic field that changes with time generates an alternating electric field, and an electric field that changes with time serves as a source of a magnetic field. These changing fields together form a common unified electromagnetic field.

The source of the electromagnetic field is the rapidly moving electric charges. Electrons, rotating around the nuclei of atoms, move with acceleration, respectively, they generate around themselves this very electromagnetic field.

When electrons move in a conductor, forming an electric current, they move with acceleration all the time, as they oscillate, that is, they change the direction of their movement all the time. The weak bond of electrons with nuclei and their ability to move freely inside the substance, and due to the existence of an electromagnetic field in conductors.

In non-conductors, electrons are much more strongly bound to the nuclei of atoms, so they cannot move freely inside the substance, and the electromagnetic fields created by them are compensated by the positively charged nuclei of atoms, so the substances remain neutral and do not conduct current.

However, the electromagnetic fields of each individual electron and proton still exist and do not differ in any way from the same fields in conductors. Therefore, non-conductors are able to be magnetized, such as hair from a comb, and then be shocked. This happens when, as a result of friction, some of the electrons nevertheless leave the atoms and uncompensated charges are formed.

Now we can confidently answer the above questions. The electric field of resting or moving charges, as well as the field obtained as a result of electromagnetic induction, do not differ from each other.

Around the magnet there is a general electromagnetic field, the electrical component of which exists regardless of whether there is a conductor nearby or not. The conductor, falling into such a field, is actually only an indicator of the electric field, and the indications of the conductor as an indicator are the electric current arising in it.

Basic concepts: magnetic field, Oersted's experiment, magnetic lines.

To study the magnetic effect of electric current, we use a magnetic needle. A magnetic needle has two poles: northern And southern. The line connecting the poles of a magnetic needle is called it. axis.

Consider an experiment showing the interaction of a conductor with current and a magnetic needle. Such an interaction was first discovered in 1820 by the Danish scientist Hans Christian Oersted (Fig. 1). His experience was of great importance for the development of the theory of electromagnetic phenomena.

Fig.1. Hans Christian Oersted.

Let us place the conductor included in the current source circuit above the magnetic needle parallel to its axis (see Fig. 2).

Fig.2. Oersted's experience.

When the circuit is closed, the magnetic needle deviates from its original position. When the circuit is opened, the magnetic needle returns to its original position. This means that the conductor with current and the magnetic needle interact with each other.

The performed experiment suggests the existence of a conductor with electric current around magnetic field. It acts on the magnetic needle, deflecting it.

A magnetic field exists around any conductor with current, i.e. around moving electric charges. Electric current and magnetic field are inseparable from each other.

Thus, around stationary electric charges there is only an electric field, around moving charges, i.e. electric current, there is electric, And a magnetic field. A magnetic field appears around a conductor when a current occurs in the latter, so the current should be considered as a source of a magnetic field. In this sense, one must understand the expressions "magnetic field of the current" or "magnetic field created by the current."

The existence of a magnetic field around a conductor carrying an electric current can be detected in various ways. One such method is to use fine iron filings.

In a magnetic field, sawdust - small pieces of iron - are magnetized and become magnetic arrows. The axis of each arrow in a magnetic field is set along the direction of action of the magnetic field forces.

Figure 3 shows a picture of the magnetic field of a straight conductor with current. To obtain such a picture, a straight conductor is passed through a sheet of cardboard. A thin layer of iron filings is poured onto the cardboard, the current is turned on and the filings are slightly shaken. Under the influence of a magnetic current field, iron filings are located around the conductor not randomly, but in concentric circles.

Fig.3. Magnetic direct current lines.

Magnetic lines are lines along which the axes of small magnetic arrows are located in a magnetic field.The direction that indicates the north pole of the magnetic needle at each point of the field is taken as the direction of the magnetic line.

The chains that iron filings form in a magnetic field show the shape of the magnetic lines of the magnetic field. The magnetic lines of the current magnetic field are closed, concentric circles.

With the help of magnetic lines it is convenient to depict magnetic fields graphically. Since a magnetic field exists at all points in space surrounding a current-carrying conductor, a magnetic line can be drawn through any point..

Figure 3a shows the location of the magnetic needles around a current-carrying conductor. (The conductor is located perpendicular to the plane of the drawing, the current in it is directed away from us, which is conventionally indicated by a circle with a cross.) The axes of these arrows are set along the magnetic lines of the direct current magnetic field. When the direction of the current in the conductor changes, all magnetic needles turn by 180 0 (Fig. 3, b; in this case, the current in the conductor is directed towards us, which is conventionally indicated by a circle with a dot.) From this experience, we can conclude that the direction of the magnetic lines of the current magnetic field is related to the direction of the current in the conductor.

Direct current magnetic field. magnetic lines. ()

Go to notes for grade 8.

Homework on this topic:

A.V. Peryshkin, E.M. Gutnik, Physics 9, Bustard, 2006:§ 56, § 57.

"Conductors in an electric field dielectrics in an electric field" - Dielectrics are materials in which there are no free electric charges. Polarization of dielectrics. Dielectrics. The use of dielectrics. According to the principle of superposition of fields, the tension inside the conductor is zero. Topic: "Conductors and dielectrics in an electric field." The charges of the sites are equal. There are three types of dielectrics: polar, non-polar and ferroelectric.

"On the Kulikovo field"- And we stand like a silent wall, Clenching our fists. And blood flowed like water. And the author of the masterpiece with a kind word - We certainly need to remember. And the brushes of Moscow ... and swords of damask ... In the morning the fog covered us with silence, Even the sandpipers fell silent. Vasnetsov "After the battle". Vavilov "Duel of Peresvet with Chelubey". And in front of the picture, I'm sure it's no coincidence, The soul can't help but tremble!

"The charge of the electric field" At what point in the field is the potential lower? 1) 1 2) 2 3) 3 4) At all points of the field, the potential is the same. An uncharged drop of liquid is divided into two parts. In an isolated system, the algebraic sum of the charges of all bodies remains constant. A charge of 10-7 C was introduced into an electric field with a strength of 200 N/C. Negative.

"Vortex electric field" - Vortex electric field. Vortex field. The induction electric field is vortex. The electric field is a vortex field. The reason for the occurrence of electric current in a stationary conductor is an electric field. Electric field.

"Field"- The stem is straight, branched, 20 - 50 cm high, covered, like the leaves, with soft hairs. Cornflower. Habitat: Underground in meadows, fields and forests. Beaver. Riddle: Did an elegant arc rise through the fields, through the meadows? Habitat: North America, Sev. and Center. Walk across the field. The mole is a small mammal with a big appetite.

"Battle of Kulikovo in Moscow"- Remember the steep descent to the high-rise building at the Yauza Gate. That on the Kulikovo field the troops of Dmitry Donskoy did not fight with the steppe nomads. Hence - and the DON, DON, i.e., the LOWER region. Explanatory Dictionary of V. Dahl). Here is Solyanka Street, which was also called KULIZHKI, that is, Kulishki. That there were no conquerors in Rus' at that time.