Around what charges does a magnetic field exist? Prepared by I.A.

Around any current-carrying conductor, i.e. moving electric charges, there is a magnetic field. The current should be considered as a source of magnetic field! Around stationary electric charges there is only electric field, and around moving charges – both electric and magnetic. HANS ØRSTED ()

1. A magnetic field occurs only near moving electric charges. 2. It weakens as it moves away from the current-carrying conductor (or moving charge) and the exact boundaries of the field cannot be specified. 3. Acts on magnetic needles in a certain way 4. Has energy and has its own internal structure, which is displayed using magnetic field lines. The magnetic lines of the magnetic field of the current are closed lines, covering the conductor

If circuits with current are connected in series in one place in space, then such a formation is called a solenoid. The magnetic field is concentrated inside the solenoid, scattered outside, and the magnetic field lines inside the solenoid are parallel to each other and the field inside the solenoid is considered homogeneous, outside the solenoid - inhomogeneous. By placing a steel rod inside the solenoid, we get a simple electromagnet. All other things being equal, the magnetic field of the electromagnet is much stronger than the magnetic field of the solenoid.

Do the Earth's magnetic poles coincide with the geographic poles? Has the location of the magnetic poles changed in the history of the planet? What is a reliable protector of life on Earth from cosmic rays? What is the reason for the appearance magnetic storms on our planet? What are magnetic anomalies associated with? Why does the magnetic needle have a very definite direction in every place on Earth? Where is she pointing?

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

To study magnetic action electric current, let's use a magnetic needle. A magnetic needle has two poles: northern And southern. The line connecting the poles of the magnetic needle is called axis.

Let's consider an experiment showing the interaction of a conductor with current and a magnetic needle. This interaction was first discovered in 1820 by the Danish scientist Hans Christian Oersted (Fig. 1). His experience was great value for the development of the doctrine of electromagnetic phenomena.

Fig.1. Hans Christian Oersted.

Let's place the conductor connected to 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 current-carrying conductor and the magnetic needle interact with each other.

The experiment carried out 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 current-carrying conductor, 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 magnetic field. A magnetic field appears around a conductor when a current arises in the latter, so the current should be considered as a source of the magnetic field. In this sense, we must understand the expressions “magnetic field of current” or “magnetic field created by current.”

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

In a magnetic field, filings - small pieces of iron - become 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 carrying 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 lightly shaken. Under the influence of the magnetic field of the current, iron filings are located around the conductor not randomly, but in concentric circles.

Fig.3. Direct current magnetic lines.

Magnetic lines are lines along which the axes of small magnetic needles are located in a magnetic field.The direction indicated by the north pole of the magnetic needle at each point in the field is taken to be 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 magnetic field of the current are closed, concentric circles.

Using 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 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 installed along the magnetic lines of the direct current magnetic field. When the direction of the current in the conductor changes, all magnetic needles rotate by 180 0 (Fig. 3b; in this case, the current in the conductor is directed towards us, which is conventionally indicated by a circle with a dot.) From this experiment we can conclude that the direction of the magnetic lines of the magnetic field of the current is related to the direction of the current in the conductor.

Direct current magnetic field. Magnetic lines. ()

Go to notes for 8th grade.

Homework on this topic:

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

The term “field” in Russian refers to a very large space of homogeneous composition, for example, wheat or potato.

In physics and electrical engineering it is used to describe various types matter, for example, electromagnetic matter, consisting of electric and magnetic components.

Electric charge is associated with these forms of matter. When it is motionless, there is always an electric field around it, and when it moves, a magnetic field is also formed.

Man's idea of ​​the nature of electricity (more precise definition- electrostatic) field was formed on the basis of experimental research of its properties, because no other method of studying exists yet. With this method, it has been revealed that it acts on moving and/or stationary electrical charges with a certain force. By measuring its value, the main operational characteristics are assessed.

Electric field

It is formed:

around electric charges (bodies or particles);

when the magnetic field changes, as, for example, occurs during movement.

It is depicted by lines of force, which are usually shown emanating from positive charges and ending in negative ones. Thus, charges are sources of electric field. By acting on them you can:

detect the presence of a field;

enter a calibrated value to measure its value.

For practical use a power characteristic is selected, called tension, which is assessed by the effect on a unit charge of a positive sign.

It works on:

electrical bodies and charges in motion with a certain force;

magnetic moments without taking into account the states of their motion.

The magnetic field is created:

the passage of a current of charged particles;

summing up the magnetic moments of electrons inside atoms or other particles;

with a temporary change in the electric field.

It is also depicted by lines of force, but they are closed along a contour and have no beginning or end, in contrast to electrical lines.

Interaction of electric and magnetic fields

The first theoretical and mathematical justification of the processes occurring inside electromagnetic field, completed by James Clerk Maxwell. He presented a system of equations of differential and integral forms, in which he showed the connections of the electromagnetic field with electric charges and flowing currents inside continuous media or vacuum.

In his work he used the following laws:

Amperes, which describe the flow of current through a conductor and the creation of magnetic induction around it;

Faraday, explaining the occurrence of electric current from the action of an alternating magnetic field on a closed conductor.

Maxwell's works determined the exact relationships between the manifestations of electric and magnetic fields, depending on the charges distributed in space.

A lot of time has passed since the publication of Maxwell's works. Scientists are constantly studying the manifestations of experimental facts between electric and magnetic fields, but even now it is not particularly possible to find out their nature. Results are limited purely practical application the phenomena under consideration.

This is explained by the fact that with our level of knowledge we can only build hypotheses, because for now we are only able to assume something. After all, nature has inexhaustible properties that still need to be studied extensively and for a long time.

Comparative characteristics of electric and magnetic fields

Sources of education

The mutual connection between the fields of electricity and magnetism helps to understand the obvious fact: they are not separate, but connected, but can manifest themselves in different ways, being a single whole - an electromagnetic field.

If we imagine that at some point in space a non-uniform electric charge field has been created, motionless relative to the Earth’s surface, then it will not be possible to determine the magnetic field around it at rest.

If the observer begins to move relative to this charge, then the field will begin to change over time and the electrical component will already form a magnetic component, which a persistent researcher can see with his measuring instruments.

In a similar way, these phenomena will manifest themselves when a stationary magnet is located on some surface, creating a magnetic field. When the observer begins to move relative to it, he will detect the appearance of an electric current. This process describes the phenomenon of electromagnetic induction.

Therefore, to say that at the point in space under consideration there is only one of two fields: electric or magnetic, does not make much sense. This question must be posed in relation to the reference system:

stationary;

mobile.

In other words, the reference frame affects the manifestation of the electric and magnetic fields in the same way as viewing landscapes through filters of different shades. Changing the color of the glass affects our perception of the overall picture, but even if we take as a basis the natural light created by the passage sun rays through the air atmosphere, will not give a true picture as a whole, will distort it.

This means that the reference system is one of the ways to study the electromagnetic field and allows us to judge its properties and configuration. But it does not have absolute significance.

Electromagnetic field indicators

Electric field

Electrically charged bodies are used as indicators indicating the presence of a field in a certain place in space. They can use electrified small pieces of paper, balls, sleeves, and “sultanas” to observe the electrical component.

Let's consider an example when two indicator balls are located on both sides of a flat electrified dielectric on a free suspension. They will be equally attracted to its surface and will stretch into a single line.

At the second stage, we place a flat metal plate between one of the balls and the electrified dielectric. It will not change the forces acting on the indicators. The balls will not change their position.

The third stage of the experiment involves grounding the metal sheet. As soon as this happens, the indicator ball located between the electrified dielectric and the grounded metal will change its position, changing direction to vertical. It will no longer be attracted to the plate and will be subject only to the gravitational forces of gravity.

This experience shows that grounded metal shields block the propagation of electric field lines.

In this case, indicators can be:

steel filings;

a closed circuit with electric current flowing through it;

magnetic needle (example with a compass).

The principle of distributing steel filings along magnetic lines of force is the most common. It is also incorporated into the work of the magnetic needle, which, in order to reduce the counteraction of frictional forces, is fixed on a sharp tip and thereby receives additional freedom for rotation.

Laws describing the interactions of fields with charged bodies

Electric fields

The picture of the processes occurring inside electric fields was clarified by Coulomb's experimental work, carried out with point charges suspended on a thin and long thread of quartz.

When a charged ball was brought closer to them, the latter influenced their position, causing them to deviate by a certain amount. This value was recorded on the scale dial of a specially designed device.

In this way, the forces of mutual action between electric charges, called . They are described by mathematical formulas that allow preliminary calculations designed devices.

Magnetic fields

It works well here based on the interaction of a conductor with a current placed inside magnetic field lines.

To direct the force acting on a conductor with current flowing through it, a rule is used that uses the arrangement of the fingers on the left hand. The four fingers connected together must be positioned in the direction of the current, and the magnetic field lines must enter the palm. Then bulging thumb will indicate the direction of action of the desired force.

Graphic images of fields

To designate them on the drawing plane, force lines are used.

Electric fields

To designate tension lines in this situation, a potential field is used when there are stationary charges. power line leaves the positive charge and goes to the negative one.

An example of modeling an electric field is the placement of quinine crystals in oil. More in a modern way considered use computer programs graphic designers.

They allow you to create images of equipotential surfaces and judge numerical value electric field, analyze various situations.

Magnetic fields

For clarity of display, they use lines characteristic of a vortex field when they are closed by a single contour. The example given earlier with steel filings clearly depicts this phenomenon.

Power characteristics

They are usually expressed as vector quantities having:

a certain direction of action;

force value calculated using the appropriate formula.

Electric fields

The electric field strength vector of a unit charge can be represented in the form of a three-dimensional image.

Its size:

directed from the center of the charge;

has a dimension depending on the calculation method;

determined by non-contact action, that is, at a distance, as a ratio acting force to charge.

Magnetic fields

The tension arising in the coil can be seen in the following picture.

Magnetic force lines in it from each turn with outside have the same direction and add up. Inside the interturn space they are directed counter. Due to this internal field weakened.

The magnitude of tension is affected by:

the strength of the current passing through the winding;

the number and density of winding turns, which determine the axial length of the coil.

Increased currents increase magnetomotive force. In addition, in two coils with equal number turns, but with different winding densities, when the same current passes, this force will be higher where the turns are located closer.

Thus, electrical and magnetic field have completely definite differences, but are interconnected components of a single common thing - electromagnetic.

“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. Application of dielectrics. According to the principle of field superposition, the tension inside the conductor is zero. Topic: “Conductors and dielectrics in an electric field.” The charges of the platforms are equal. There are three types of dielectrics: polar, non-polar and ferroelectrics.

“On the Kulikovo field” - And we stand as a silent wall, Clenching our fists. And blood flowed like water. And the author of the masterpiece kind words“We definitely need to remember.” And the Moscow brushes... and the damask swords... In the morning, the fog covered us with silence, Even the waders fell silent. Vasnetsov “After the massacre.” Vavilov “Duel of Peresvet with Chelubey”. And before the picture, I’m sure it’s no coincidence, the Soul can’t help but tremble!

“Electric field charge” - At which point in the field is the potential less? 1) 1 2) 2 3) 3 4) The potential is the same at all points of the field. An uncharged drop of liquid splits 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 of intensity 200 N/C. Negative.

“Vortex electric field” - Vortex electric field. Vortex field. The inductive electric field is vortex. The electric field is a vortex field. The reason for the occurrence of electric current in a stationary conductor is the electric field. Electric field.

“Field” - The stem is straight, branched, 20 - 50 cm high, covered, like the leaves, with soft hairs. Knapweed. Habitat: Underground in meadows, fields and forests. Beaver. Riddle: A graceful arc has arisen across the fields, across the meadows? Habitat: North America, North and Center. Walk through 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 Yauz Gate. That on the Kulikovo Field the troops of Dmitry Donskoy did not fight with steppe nomads. Hence the DON, DON, i.e. LOWER region. Explanatory Dictionary V. Dahl). Here is Solyanka Street, which was previously also called KULIZHKI, i.e. Kulishki. About the fact that there were no conquerors in Rus' at that time.