Induction current. Induction current How to create short-term induction current

You already know that there is always a magnetic field around an electric current. Electric current and magnetic field are inseparable from each other.

But if electricity, as they say, “creates” a magnetic field, then isn’t there an opposite phenomenon? Is it possible to “create” an electric current using a magnetic field?

Such a task at the beginning of the 19th century. Many scientists have tried to solve it. The English scientist Michael Faraday also put it before himself. “Convert magnetism into electricity” - this is how Faraday wrote this problem in his diary in 1822. It took the scientist almost 10 years of hard work to solve it.

Michael Faraday (1791-1867)
English physicist. Discovered the phenomenon of electromagnetic induction, extra-currents during closing and opening

To understand how Faraday was able to “turn magnetism into electricity,” let’s perform some of Faraday’s experiments using modern instruments.

Figure 119, a shows that if a magnet is moved into a coil closed to a galvanometer, the galvanometer needle is deflected, indicating the appearance of an inductive (induced) current in the coil circuit. The induced current in a conductor represents the same ordered movement of electrons as the current obtained from galvanic cell or battery. The name “induction” only indicates the reason for its occurrence.

Rice. 119. The occurrence of induction current when a magnet and coil move relative to each other

When the magnet is removed from the coil, a deflection of the galvanometer needle is again observed, but in the opposite direction, which indicates the occurrence of a current in the coil in the opposite direction.

As soon as the movement of the magnet relative to the coil stops, the current stops. Consequently, current in the coil circuit exists only while the magnet is moving relative to the coil.

Experience can be changed. We will put a coil on a stationary magnet and remove it (Fig. 119, b). And again you can find that as the coil moves relative to the magnet, current appears again in the circuit.

Figure 120 shows coil A connected to the current source circuit. This coil is inserted into another coil C connected to the galvanometer. When the circuit of coil A is closed and opened, an induced current appears in coil C.

Rice. 120. The occurrence of induction current when closing and opening an electrical circuit

You can cause the appearance of an induction current in coil C by changing the current strength in coil A or by moving these coils relative to each other.

Let's do one more experiment. Let's place a flat contour of a conductor in a magnetic field, the ends of which will be connected to a galvanometer (Fig. 121, a). When the circuit is rotated, the galvanometer notes the appearance of an induction current in it. A current will also appear if a magnet is rotated near the circuit or inside it (Fig. 121, b).

Rice. 121. When a circuit rotates in a magnetic field (magnet relative to the circuit), a change in magnetic flux leads to the appearance of an induced current

In all the experiments considered, the induced current arose when the magnetic flux piercing the area covered by the conductor changed.

In the cases shown in Figures 119 and 120, the magnetic flux changed due to a change in the magnetic field induction. Indeed, when the magnet and the coil moved relative to each other (see Fig. 119), the coil fell into field areas with greater or lesser magnetic induction (since the magnet’s field is non-uniform). When the circuit of coil A (see Fig. 120) was closed and opened, the induction of the magnetic field created by this coil changed due to a change in the current strength in it.

When a wire loop was rotated in a magnetic field (see Fig. 121, a) or a magnet relative to the loop (see Fig. 121, b"), the magnetic flux changed due to a change in the orientation of this loop relative to the lines of magnetic induction.

Thus,

• with any change in the magnetic flux penetrating the area limited by a closed conductor, an electric current arises in this conductor, existing throughout the entire process of changing the magnetic flux

This is the phenomenon of electromagnetic induction.

The discovery of electromagnetic induction is one of the most remarkable scientific achievements of the first half of the 19th century. It caused the emergence and rapid development of electrical engineering and radio engineering.

Based on the phenomenon of electromagnetic induction, powerful electrical energy generators were created, in the development of which scientists and technicians took part different countries. Among them were our compatriots: Emilius Khristianovich Lenz, Boris Semenovich Jacobi, Mikhail Iosifovich Dolivo-Dobrovolsky and others, who made a great contribution to the development of electrical engineering.

Questions

1. What was the purpose of the experiments depicted in Figures 119-121? How were they carried out?
2. Under what condition in the experiments (see Fig. 119, 120) did an induced current arise in a coil closed to a galvanometer?
3. What is the phenomenon of electromagnetic induction?
4. What is the importance of the discovery of the phenomenon of electromagnetic induction?

Exercise 36

1. How to create a short-term induction current in the K 2 coil shown in Figure 118?
2. The wire ring is placed in a uniform magnetic field (Fig. 122). The arrows shown next to the ring show that in cases a and b the ring moves rectilinearly along the lines of induction of the magnetic field, and in cases c, d and e it rotates around the axis OO." In which of these cases can an induced current arise in the ring ?

Questions.

1. What was the purpose of the experiments depicted in Figures 126-128? How were they carried out?

The experiments were carried out with the aim of creating and determining the conditions for the occurrence of an induction current. To do this, in the first two experiments (Fig. 126), a coil connected to a galvanometer and a magnet were used. In the first experiment, a magnet was moved, in the second, a coil was moved. In the third experiment (Fig. 127), the magnet was replaced with a second coil connected to the circuit. In the fourth and fifth (Fig. 128), the frame was rotated inside the magnet (a) and the magnet inside the frame (b).

2. Under what condition did an induced current arise in all experiments in a coil closed to a galvanometer?

The current arose when the magnetic field changed.

3. What is the phenomenon of electromagnetic induction?

When the magnetic flux piercing the circuit of a closed conductor changes, an electric current arises in this conductor, which does not stop while the change occurs.

4. What is the importance of the discovery of the phenomenon of electromagnetic induction?

The discovery of electromagnetic induction made it possible to produce electric current on an industrial scale, as electrical energy generators were created.

Exercises.

1. How to create a short-term induction current in the K2 coil shown in Figure 125?

By any method that changes the current strength in the circuit and, accordingly, the magnetic flux: 1) rheostat; 2) key; 3) changing the position of the coil K 2.

2. The wire ring is placed in a uniform magnetic field (Fig. 129). The arrows shown next to the ring show that in cases a and b the ring moves rectilinearly along the lines of induction of the magnetic field, and in cases c, d and e it rotates around the axis OO." In which of these cases can an induced current arise in the ring ?

Induction current occurs in case d), because At the same time, the magnetic flux penetrating the ring changes.

INDUCTION CURRENT is an electric current that occurs when the flux of magnetic induction changes in a closed conductive circuit. This phenomenon is called electromagnetic induction. Do you want to know which direction is the induction current? Rosinductor is a trade information portal where you will find information about current.

The rule determining the direction of the induction current is as follows: “The induction current is directed so as to counteract with its magnetic field the change in the magnetic flux that causes it.” The right hand is turned with the palm towards the magnetic lines of force, with the thumb directed towards the movement of the conductor, and the four fingers indicate in which direction the induced current will flow. By moving a conductor, we move along with the conductor all the electrons contained in it, and when moving electric charges in a magnetic field, a force will act on them according to the left-hand rule.

The direction of the induction current, as well as its magnitude, is determined by Lenz’s rule, which states that the direction of the induction current always weakens the effect of the factor that excited the current. When the magnetic field flux through the circuit changes, the direction of the induced current will be such as to compensate for these changes. When a magnetic field exciting a current in a circuit is created in another circuit, the direction of the induction current depends on the nature of the changes: when the external current increases, the induction current has the opposite direction; when it decreases, it is directed in the same direction and tends to increase the flow.

An induction current coil has two poles (north and south), which are determined depending on the direction of the current: the induction lines exit from the north pole. The approach of a magnet to a coil causes a current to appear in a direction that repels the magnet. When the magnet is removed, the current in the coil has a direction that favors the attraction of the magnet.

Induction current occurs in a closed circuit located in an alternating magnetic field. The circuit can be either stationary (placed in a changing flux of magnetic induction) or moving (the movement of the circuit causes a change in the magnetic flux). The occurrence of an induction current causes a vortex electric field, which is excited under the influence of a magnetic field.

You can learn how to create a short-term induced current from a school physics course.

There are several ways to do this:

• - movement of a permanent magnet or electromagnet relative to the coil,
• - movement of the core relative to the electromagnet inserted into the coil,
• - closing and opening the circuit,
• - regulation of current in the circuit.

The basic law of electrodynamics (Faraday's law) states that the strength of the induced current for any circuit is equal to the rate of change of the magnetic flux passing through the circuit, taken with a minus sign. The strength of the induction current is called electromotive force.

In N 1 S 1. the magnetic field is clearly depicted; closed lines; 2. closed lines; 3. The direction to which the north pole of the magnetic needle points is taken as the direction of the field lines, i.e. the lines of force are directed from the north pole (N) of the permanent magnet to the south pole (S). Magnetic field lines: FIG.1

VECTOR OF MAGNETIC INDUCTION. MAGNETIC LINES. B is the magnetic induction vector, always directed along the tangent to the magnetic induction lines; B – is the strength characteristic of the magnetic field; The modulus of the magnetic induction vector of a uniform magnetic field is equal to the ratio of the modulus of the force with which the magnetic field acts on a current-carrying conductor located perpendicular to the lines of magnetic induction, to the current strength and the length of the conductor

A uniform magnetic field is a field, at each point of which A uniform magnetic field is a field, at each point of which there is 1. magnetic lines, distributed with equal density, or parallel to each other; 2. magnetic vectors in induction have the same magnitude and direction. homogeneous. Otherwise the field is non-uniform. Uniform and non-uniform magnetic field. Fig.2 Fig. 3 fig. 4 fig. 5 B

Magnetic field of direct current, the rule of the “gimlet” or the right hand - allows you to determine the direction of the magnetic field lines generated by the conductor with current: if you take the conductor with current in your right hand so that the thumb indicates the direction of the current, then the remaining fingers of the hand covering the conductor , indicate the direction of the magnetic field lines; FIG.6

Frame drain is a conductor bent in the form of a rectangle or circle through which direct current flows; - it creates a magnetic field similar to the magnetic field of a permanent strip magnet and is a simple electromagnet; - if the fingers of the right hand are squeezed in the direction corresponding to the direction of the current in the frame, then the thumb will indicate the direction from the south pole to the north; By applying the right-hand rule, you can determine the north and south poles of the magnetic field of the frame with current: FIG.7

Solenoid is a coiled conductor through which electric current flows; Solenoid is a coiled conductor through which electric current flows; the magnetic field of the solenoid is similar to the magnetic field of a strip magnet; Structurally, the solenoid is a circular frame with current connected in series; You can determine the north and south poles of the magnetic field of the solenoid by applying the right-hand rule to the current loop. FIG.8

AMPERE FORCE is the force acting on a current-carrying conductor placed in a magnetic field; is equal to the product of the magnitude of the magnetic induction vector B by the current strength I, the length of the conductor section l and the sine of the angle α between the magnetic induction and the conductor section. direction of the Ampere force rule of the left hand - if the palm of the left hand is positioned so that the magnetic induction lines enter it, and the four extended fingers are placed in the direction of the current in the conductor, then the bent thumb will show the direction of the Ampere force acting on the current; FIG.9

LORENTZ FORCE is a force acting on a moving charged particle from an external magnetic field; is equal to the product of the charge q by the magnetic induction B, the speed of motion of the particle υ and by the sine of the angle α between the direction of the charge velocity and the magnetic field induction DIRECTION OF THE LORENTZ FORCE: if the palm of the left hand is positioned so that vector B enters it, and four extended fingers are directed along vector υ, then the bent thumb will show the direction of the force acting on the positive charge. if the palm of the right hand is positioned so that vector B enters it, and four extended fingers are directed along vector υ, then the bent thumb will show the direction of the force acting on the negative charge. FIG.15

MAGNETIC FLUX (FLUX OF MAGNETIC INDUCTION): CHARACTERIZES THE DISTRIBUTION OF MAGNETIC FIELD OVER A SURFACE LIMITED BY A CLOSED LOOP; VALUE EQUAL TO THE PRODUCT OF THE MAGNETIC INDUCTION VECTOR MODULE AND THE CIRCUIT AREA AND THE COSINE OF THE ANGLE BETWEEN THE MAGNETIC INDUCTION VECTOR AND THE NORMAL TO THE SURFACE; MAGNETIC FLUX (FLUX OF MAGNETIC INDUCTION): CHARACTERIZES THE DISTRIBUTION OF MAGNETIC FIELD OVER A SURFACE LIMITED BY A CLOSED LOOP; VALUE EQUAL TO THE PRODUCT OF THE MAGNETIC INDUCTION VECTOR MODULE AND THE CIRCUIT AREA AND THE COSINE OF THE ANGLE BETWEEN THE MAGNETIC INDUCTION VECTOR AND THE NORMAL TO THE SURFACE;

ELECTROMAGNETIC INDUCTION ELECTROMAGNETIC INDUCTION THE PHENOMENON OF ELECTROMAGNETIC INDUCTION WAS EXPERIMENTALLY DISCOVERED BY MICHAEL FARADAY IN 1831. THE PHENOMENON OF ELECTROMAGNETIC INDUCTION IS THE PHENOMENON OF THE APPEARANCE OF AN ELECTROMOTIVE FORCE IN A CONDUCTOR LOCATED IN AN ALTERNATING MAGNETIC FIELD OR MOVING IN A CONSTANT MAGNETIC FIELD.

THE INDUCED (VORTEX) FIELD is not created electric charges, and by a change in the magnetic field; The lines of force of the induced field are closed, and the field itself has a vortex character; INDUCTION CURRENT – occurs in a closed conductor under the influence of an induced (vortex) field. THE INDUCTION CURRENT IN THE COIL C, OR IN A CLOSED LOOP, APPEARS WHEN THE MAGNETIC FLUX CHANGES, PERPETING THE AREA LIMITED BY THE CONDUCTOR: 1. WHEN THE MAGNET MOVES; 2. WHEN THE CURRENT STRENGTH CHANGES IN COIL A; 3. WHEN COILS A AND C MOVE RELATIVE TO EACH OTHER; 4. WHEN A CLOSED LOOP ROTATES IN A MAGNETIC FIELD; 5. WHEN THE MAGNET ROTATES NEAR THE CIRCUIT OR INSIDE IT. THE INDUCTION CURRENT IN THE COIL C, OR IN A CLOSED LOOP, APPEARS WHEN THE MAGNETIC FLUX CHANGES, PERPETING THE AREA LIMITED BY THE CONDUCTOR: 1. WHEN THE MAGNET MOVES; 2. WHEN THE CURRENT STRENGTH CHANGES IN COIL A; 3. WHEN COILS A AND C MOVE RELATIVE TO EACH OTHER; 4. WHEN A CLOSED LOOP ROTATES IN A MAGNETIC FIELD; 5. WHEN THE MAGNET ROTATES NEAR THE CIRCUIT OR INSIDE IT. CONCLUSION: