The strength of the induction current depends on the rate of change of the magnetic flux. What determines the strength and direction of the induction current?

If there is a closed conducting loop in a magnetic field that does not contain current sources, then when the magnetic field changes in the loop, electricity. This phenomenon is called electromagnetic induction. The appearance of a current indicates the emergence of an electric field in the circuit, which can provide closed motion electric charges or, in other words, about the occurrence of EMF. The electric field, which arises when the magnetic field changes and the work of which when moving charges along a closed circuit is not equal to zero, has closed power lines and is called a vortex.

To quantitatively describe electromagnetic induction, the concept is introduced magnetic flux(or flux of the magnetic induction vector) through a closed loop. For a flat contour located in a uniform magnetic field (and only such situations can be encountered by schoolchildren on the unified state exam), the magnetic flux is defined as

where is the field induction, is the contour area, is the angle between the induction vector and the normal (perpendicular) to the contour plane (see figure; the perpendicular to the contour plane is shown by a dotted line). Unit of magnetic flux in international system The SI unit of measurement is Weber (Wb), which is defined as the magnetic flux through a contour of an area of ​​1 m 2 of a uniform magnetic field with an induction of 1 T, perpendicular to the plane contour.

The magnitude of the induced emf that occurs in a circuit when the magnetic flux through this circuit changes is equal to the rate of change of the magnetic flux

Here is the change in magnetic flux through the circuit over a short time interval. An important property of the law of electromagnetic induction (23.2) is its universality in relation to the reasons for changes in magnetic flux: the magnetic flux through the circuit can change due to a change in the magnetic field induction, a change in the area of ​​the circuit or a change in the angle between the induction vector and the normal, which occurs when the circuit rotates in field. In all these cases, according to law (23.2), an induced emf and an induced current will appear in the circuit.

The minus sign in formula (23.2) is “responsible” for the direction of the current resulting from electromagnetic induction (Lenz’s rule). However, it is not so easy to understand in the language of the law (23.2) to which direction of the induction current this sign will lead with a particular change in the magnetic flux through the circuit. But it’s quite easy to remember the result: the induced current will be directed in such a way that the magnetic field it creates will “tend” to compensate for the change in the external magnetic field that generated this current. For example, when the flux of an external magnetic field through a circuit increases, an induced current will appear in it, the magnetic field of which will be directed opposite to the external magnetic field so as to reduce the external field and thus maintain the original value of the magnetic field. When the field flux through the circuit decreases, the induced current field will be directed in the same way as the external magnetic field.

If the current in a circuit with current changes for some reason, then the magnetic flux through the circuit of the magnetic field that is created by this current itself also changes. Then, according to law (23.2), an induced emf should appear in the circuit. The phenomenon of the occurrence of induced emf in some electrical circuit as a result of a change in current in this circuit itself is called self-induction. To find Self-induced emf in some electrical circuit it is necessary to calculate the flux of the magnetic field created by this circuit through itself. Such a calculation presents a difficult problem due to the inhomogeneity of the magnetic field. However, one property of this flow is obvious. Since the magnetic field created by the current in the circuit is proportional to the magnitude of the current, the magnetic flux of its own field through the circuit is proportional to the current in this circuit

where is the current strength in the circuit, is the proportionality coefficient, which characterizes the “geometry” of the circuit, but does not depend on the current in it and is called the inductance of this circuit. The SI unit of inductance is Henry (H). 1 H is defined as the inductance of such a circuit, the induction flux of its own magnetic field through which is equal to 1 Wb with a current strength of 1 A. Taking into account the definition of inductance (23.3) from the law of electromagnetic induction (23.2), we obtain for the self-induction EMF

Due to the phenomenon of self-induction, the current in any electrical circuit has a certain “inertia” and, therefore, energy. Indeed, to create a current in the circuit, it is necessary to do work to overcome the self-induction EMF. The energy of the current circuit is equal to this work. It is necessary to remember the formula for the energy of a current circuit

where is the inductance of the circuit, is the current strength in it.

The phenomenon of electromagnetic induction is widely used in technology. The creation of electric current in electric generators and power plants is based on it. Thanks to the law of electromagnetic induction, a transformation occurs mechanical vibrations in electric microphones. Based on the law of electromagnetic induction, it works, in particular, electrical circuit, which is called an oscillatory circuit (see the next chapter), and which is the basis of any radio transmitting or receiving equipment.

Let's now consider the tasks.

Of those listed in problem 23.1.1 phenomena, there is only one consequence of the law of electromagnetic induction - the appearance of current in the ring when passing through it permanent magnet(answer 3 ). Everything else is the result of the magnetic interaction of currents.

As stated in the introduction to this chapter, the phenomenon of electromagnetic induction underlies the operation of the generator alternating current (problem 23.1.2), i.e. device that creates alternating current at a given frequency (answer 2 ).

The induction of the magnetic field created by a permanent magnet decreases with increasing distance to it. Therefore, when the magnet approaches the ring ( problem 23.1.3) the flux of the magnetic field of the magnet through the ring changes, and an induced current appears in the ring. Obviously, this will happen as the magnet approaches the ring with both the north and south poles. But the direction of the induction current in these cases will be different. This is due to the fact that when a magnet approaches the ring with different poles, the field in the plane of the ring in one case will be directed opposite to the field in the other. Therefore, to compensate for these changes in the external field, the magnetic field of the induced current must be directed differently in these cases. Therefore, the directions of the induction currents in the ring will be opposite (answer 4 ).

For induced emf to occur in the ring, it is necessary that the magnetic flux through the ring changes. And since the magnetic induction of a magnet’s field depends on the distance to it, then in the considered problem 23.1.4 In this case, the flow through the ring will change, and an induced current will arise in the ring (answer 1 ).

When rotating the frame 1 ( problem 23.1.5) the angle between the lines of magnetic induction (and, therefore, the induction vector) and the plane of the frame at any time equal to zero. Consequently, the magnetic flux through frame 1 does not change (see formula (23.1)), and the induced current does not arise in it. In frame 2, an induction current will arise: in the position shown in the figure, the magnetic flux through it is zero, when the frame turns a quarter turn it will be equal to , where is the induction and is the area of ​​the frame. After another quarter turn, the flow will again be zero, etc. Therefore, the flux of magnetic induction through frame 2 changes during its rotation, therefore, an induced current appears in it (answer 2 ).

IN problem 23.1.6 induced current occurs only in case 2 (answer 2 ). Indeed, in case 1, the frame, when moving, remains at the same distance from the conductor, and, therefore, the magnetic field created by this conductor in the plane of the frame does not change. When the frame moves away from the conductor, the magnetic induction of the conductor's field in the area of ​​the frame changes, the magnetic flux through the frame changes, and an induced current appears

The law of electromagnetic induction states that an induced current will flow in a ring at times when the magnetic flux through the ring changes. Therefore, while the magnet is at rest near the ring ( problem 23.1.7) no induced current will flow in the ring. Therefore, the correct answer in this problem is 2 .

According to the law of electromagnetic induction (23.2), the induced emf in the frame is determined by the rate of change of the magnetic flux through it. And since by condition problems 23.1.8 the magnetic field induction in the frame area changes uniformly, the rate of its change is constant, the value of the induced emf does not change during the experiment (answer 3 ).

IN problem 23.1.9 The induced emf arising in the frame in the second case is four times greater than the induced emf arising in the first (answer 4 ). This is due to a fourfold increase in the frame area and, accordingly, the magnetic flux through it in the second case.

IN task 23.1.10 in the second case, the rate of change of the magnetic flux doubles (the field induction changes by the same amount, but in half the time). Therefore, the emf of electromagnetic induction that occurs in the frame in the second case is twice as large as in the first (answer 1 ).

When the current in a closed conductor doubles ( problem 23.2.1), the magnitude of the magnetic field induction will double at each point in space without changing in direction. Therefore, the magnetic flux through any small area and, accordingly, the entire conductor (answer 1 ). But the ratio of the magnetic flux through a conductor to the current in this conductor, which represents the inductance of the conductor , it will not change ( problem 23.2.2- answer 3 ).

Using formula (23.3) we find in problem 32.2.3 Gn (answer 4 ).

The relationship between the units of magnetic flux, magnetic induction and inductance ( problem 23.2.4) follows from the definition of inductance (23.3): a unit of magnetic flux (Wb) is equal to the product of a unit of current (A) by a unit of inductance (H) - answer 3 .

According to formula (23.5), with a twofold increase in the inductance of the coil and a twofold decrease in the current in it ( problem 23.2.5) the energy of the magnetic field of the coil will decrease by 2 times (answer 2 ).

When the frame rotates in a uniform magnetic field, the magnetic flux through the frame changes due to a change in the angle between the perpendicular to the plane of the frame and the magnetic field induction vector. And since in both the first and second cases problem 23.2.6 this angle changes according to the same law (according to the condition, the frequency of rotation of the frames is the same), then the induced emf changes according to the same law, and, therefore, the ratio of the amplitude values ​​of the induced emf within the frame is equal to unity (answer 2 ).

Magnetic field created by a current-carrying conductor in the frame area ( problem 23.2.7), directed “from us” (see solutions to problems in Chapter 22). The magnitude of the field induction of the wire in the area of ​​the frame will decrease as it moves away from the wire. Therefore, the induced current in the frame should create a magnetic field directed inside the frame “away from us”. Using now the gimlet rule to find the direction of magnetic induction, we conclude that the induced current in the frame will be directed clockwise (answer 1 ).

As the current in the wire increases, the magnetic field it creates will increase and an induced current will appear in the frame ( problem 23.2.8). As a result, there will be an interaction between the induction current in the frame and the current in the conductor. To find the direction of this interaction (attraction or repulsion), you can find the direction of the induction current, and then, using the Ampere formula, the force of interaction between the frame and the wire. But you can do it differently, using Lenz's rule. All inductive phenomena must have such a direction as to compensate for the cause that causes them. And since the reason is an increase in current in the frame, the force of interaction between the induction current and the wire should tend to reduce the magnetic flux of the wire's field through the frame. And since the magnetic induction of the wire’s field decreases with increasing distance to it, this force will push the frame away from the wire (answer 2 ). If the current in the wire decreased, the frame would be attracted to the wire.

Problem 23.2.9 also related to the direction of induction phenomena and Lenz's rule. When a magnet approaches a conducting ring, an induced current will arise in it, and its direction will be such as to compensate for the cause that causes it. And since this reason is the approach of the magnet, the ring will be repelled from it (answer 2 ). If the magnet is moved away from the ring, then for the same reasons an attraction of the ring to the magnet would arise.

Problem 23.2.10 is the only computational problem in this chapter. To find the induced emf you need to find the change in magnetic flux through the circuit . It can be done like this. Let at some point in time the jumper be in the position shown in the figure, and let a small time interval pass. During this time interval, the jumper will move by an amount. This will lead to an increase in the contour area by the amount . Therefore, the change in magnetic flux through the circuit will be equal to , and the magnitude of the induced emf (answer 4 ).

Topic 11. PHENOMENON OF ELECTROMAGNETIC INDUCTION.

11.1. Faraday's experiments. Induction current. Lenz's rule. 11.2. The magnitude of the induced emf.

11.3. The nature of induced emf.

11.4. Circulation of the vortex electric field strength vector.

11.5. Betatron.

11.6. Toki Fuko.

11.7. Skin effect.

11.1. Faraday's experiments. Induction current. Lenz's rule.

WITH Since the discovery of the connection between the magnetic field and the current (which confirms the symmetry of the laws of nature), numerous attempts have been made to obtain current using a magnetic field. The problem was solved by Michael Faraday in 1831. (The American Joseph Henry also discovered, but did not have time to publish his results. Ampere also claimed the discovery, but was not able to present his results).

Michael Faraday (1791 - 1867) - famous English physicist. Research in the field of electricity, magnetism, magnetooptics, electrochemistry. Created a laboratory model of an electric motor. He opened the extra currents when closing and opening the circuit and established their direction. He discovered the laws of electrolysis, was the first to introduce the concepts of field and dielectric constant, and in 1845 he used the term “magnetic field.”

Among other things, M. Faraday discovered the phenomena of dia and paramagnetism. He found that all materials in a magnetic field behave differently: they are oriented along the field (steam and ferromagnets) or across

fields are diamagnetic.

Faraday’s experiments are well known from the school physics course: a coil and a permanent magnet (Fig. 11.1)

Rice. 11.1 Fig. 11.2

If you bring a magnet close to the coil or vice versa, an electric current will arise in the coil. The same thing with two closely spaced coils: if an alternating current source is connected to one of the coils, then alternating current will also appear in the other

(Fig. 11.2), but this effect is best manifested if two coils are connected with a core (Fig. 11.3).

According to Faraday's definition, what these experiments have in common is that: if the flow

As the induction vector penetrating the closed, conducting circuit changes, an electric current arises in the circuit.

This phenomenon is called the phenomenon of electromagnetic induction, and the current is induction . Moreover, the phenomenon is completely independent of the method of changing the flux of the magnetic induction vector.

So, it turns out that moving charges (current) create a magnetic field, and a moving magnetic field creates (vortex) electric field and the induced current itself.

For each specific case, Faraday indicated the direction of the induction current. In 1833 Lenz established a general rule for finding the direction of current:

the induced current is always directed in such a way that the magnetic field of this current prevents the change in magnetic flux causing the induced current. This statement is called Lenz's rule.

Filling the entire space with a homogeneous magnet leads, other things being equal, to an increase in induction by µ times. This fact confirms that

the induced current is caused by a change in the flux of the magnetic induction vector B, and not the flux of the intensity vector H.

11.2. The magnitude of the induced emf.

To create current in a circuit, an electromotive force must be present. Therefore, the phenomenon of electromagnetic induction indicates that when the magnetic flux changes in the circuit, an electromotive force of induction E i arises. Our

task, using the laws of conservation of energy, find the value E i and find out it

Let's consider the movement of the moving section 1 - 2 of the circuit with current in a magnetic field

B (Fig. 11.4).

Let first there be no magnetic field B. A battery with an emf equal to E 0 creates

current I 0 . During time dt, the battery does work

dA = E I0 dt(11.2.1)

– this work will turn into heat, which can be found according to the Joule-Lenz law:

Q = dA = E 0 I0 dt = I0 2 Rdt,

here I 0 = E R 0, R is the total resistance of the entire circuit.

Let's place the circuit in a uniform magnetic field with induction B. LinesB ||n and are related to the direction of the current by the gimlet rule. FluxF associated with the circuit is positive.r

Each contour element experiences a mechanical force d F . The moving side of the frame will experience a force F 0 . Under the influence of this force, section 1 – 2

will move with speed υ = dx dt. In this case, the magnetic flux will also change.

induction.

Then, as a result of electromagnetic induction, the current in the circuit will change and become

resulting). This force will produce work dA in time dt: dA = Fdx = IdФ.

As in the case when all elements of the frame are stationary, the source of work is E 0 .

With a stationary circuit, this work was reduced only to the release of heat. In our case, heat will also be released, but in a different amount, since the current has changed. In addition, it is done mechanical work. General work for time dt, is equal to:

We have the right to consider the resulting expression as Ohm’s law for a circuit in which, in addition to the source E 0, E i acts, which is equal to:

induction running through this circuit.

This expression for the induced emf of a circuit is completely universal, independent of the method of changing the flux of magnetic induction and is called

Faraday's law.

Sign (-) – mathematical expression Lenz's rules on the direction of induction current: the induced current is always directed so that its field

counteract the change in the initial magnetic field.

The direction of the induction current and the direction d dt Ф are related gimlet rule(Fig. 11.5).

Dimension of induced emf: [ E i ] =[ Ф ] =B c =B .t c

If the circuit consists of several turns, then we must use the concept

flux linkage (total magnetic flux):

Ψ = Ф·N,

where N is the number of turns. So if

11.3. The nature of induced emf.

Let's answer the question: what is the reason for the movement of charges, the reason for the occurrence of induction current? Consider Figure 11.6.

1) If you move a conductor in a uniform magnetic field B, then under the influence of the Lorentz force, the electrons will be deflected down, and positive charges up - a potential difference arises. This will be the E i -sided force, under the influence

which current flows. As we know, for positive charges

F l = q + ; for electrons F l = –e - .

2) If the conductor is stationary and the magnetic field changes, what force excites the induced current in this case? Let's take an ordinary transformer (Fig. 11.7).

As soon as we close the circuit of the primary winding, a current immediately arises in the secondary winding. But the Lorentz force has nothing to do with it, because it acts on moving charges, and at the beginning they were at rest (they were in thermal motion - chaotic, but here we need directed motion).

The answer was given by J. Maxwell in 1860: Any alternating magnetic field excites an electric field (E") in the surrounding space. This is the reason for the occurrence of induction current in the conductor. That is, E" occurs only in the presence of an alternating magnetic field (the transformer does not work at direct current).

The essence of the phenomenon of electromagnetic induction not at all in the appearance of induction current (current appears when there are charges and the circuit is closed), and in the emergence of a vortex electric field (not only in the conductor, but also in the surrounding space, in vacuum).

This field has a completely different structure than the field created by charges. Since it is not created by charges, the lines of force cannot begin and end on charges, as we did in electrostatics. This field is a vortex, its lines of force are closed.

Since this field moves charges, it therefore has force. Let's introduce

vector of the vortex electric field strength E ". The force with which this field acts on the charge

F "= q E ".

But when a charge moves in a magnetic field, it is acted upon by the Lorentz force

Occurrence of induced emf in a conductor

If you place it in a conductor and move it so that during its movement it intersects the field lines, then something called induced emf will arise in the conductor.

An induced emf will occur in a conductor even if the conductor itself remains stationary, and the magnetic field moves, crossing the conductor with its lines of force.

If the conductor in which the induced emf is induced is closed to any external circuit, then under the influence of this emf a current called induction current.

The phenomenon of EMF induction in a conductor when it is crossed by magnetic field lines is called electromagnetic induction.

Electromagnetic induction- this is the reverse process, i.e. the conversion of mechanical energy into electrical energy.

The phenomenon of electromagnetic induction has found wide application in. The device of various electric machines.

Magnitude and direction of induced emf

Let us now consider what the magnitude and direction of the EMF induced in the conductor will be.

The magnitude of the induced emf depends on the number of field lines crossing the conductor per unit time, i.e., on the speed of movement of the conductor in the field.

The magnitude of the induced emf is directly dependent on the speed of movement of the conductor in the magnetic field.

The magnitude of the induced emf also depends on the length of that part of the conductor that is intersected by the field lines. The larger part of the conductor is crossed by the field lines, the greater the emf is induced in the conductor. And finally, the stronger the magnetic field, i.e., the greater its induction, the greater the emf that appears in the conductor crossing this field.

So, the magnitude of the induced emf that occurs in a conductor when it moves in a magnetic field is directly proportional to the induction of the magnetic field, the length of the conductor and the speed of its movement.

This dependence is expressed by the formula E = Blv,

where E is the induced emf; B - magnetic induction; I is the length of the conductor; v is the speed of movement of the conductor.

It should be firmly remembered that In a conductor moving in a magnetic field, an induced emf occurs only if this conductor is crossed by magnetic field lines. If the conductor moves along the field lines, that is, does not cross, but seems to slide along them, then no EMF is induced in it. Therefore, the above formula is valid only when the conductor moves perpendicular to the magnetic field lines.

The direction of the induced emf (as well as the current in the conductor) depends on which direction the conductor is moving. To determine the direction of the induced EMF there is a rule right hand.

If you hold the palm of your right hand so that the magnetic field lines enter it, and the bent thumb indicates the direction of movement of the conductor, then the extended four fingers will indicate the direction of action of the induced emf and the direction of the current in the conductor.

Right hand rule

Induction emf in a coil

We have already said that in order to create an inductive emf in a conductor, it is necessary to move either the conductor itself or the magnetic field in a magnetic field. In both cases, the conductor must be crossed by magnetic field lines, otherwise the EMF will not be induced. The induced EMF, and therefore the induced current, can be obtained not only in a straight conductor, but also in a conductor twisted into a coil.

When moving inside a permanent magnet, an EMF is induced in it due to the fact that the magnetic flux of the magnet crosses the turns of the coil, i.e., exactly as it was when a straight conductor moved in the field of the magnet.

If the magnet is lowered into the coil slowly, then the EMF arising in it will be so small that the needle of the device may not even deviate. If, on the contrary, the magnet is quickly inserted into the coil, then the deflection of the needle will be large. This means that the magnitude of the induced emf, and therefore the current strength in the coil, depends on the speed of movement of the magnet, i.e., on how quickly the field lines intersect the turns of the coil. If you now alternately introduce a strong magnet and then a weak one into the coil at the same speed, you will notice that with a strong magnet the needle of the device will deviate by larger angle. Means, the magnitude of the induced emf, and therefore the current strength in the coil, depends on the magnitude of the magnetic flux of the magnet.

And finally, if you introduce the same magnet at the same speed first into a coil with a large number turns, and then with significantly less, then in the first case the instrument arrow will deviate by a larger angle than in the second. This means that the magnitude of the induced emf, and therefore the current strength in the coil, depends on the number of its turns. The same results can be obtained if an electromagnet is used instead of a permanent magnet.

The direction of the induced emf in the coil depends on the direction of movement of the magnet. The law established by E. H. Lenz tells how to determine the direction of the induced emf.

Lenz's law for electromagnetic induction

Any change in the magnetic flux inside the coil is accompanied by the appearance of an induced emf in it, and the faster the magnetic flux passing through the coil changes, the greater the emf is induced in it.

If the coil in which the induced emf is created is closed to an external circuit, then an induced current flows through its turns, creating a magnetic field around the conductor, due to which the coil turns into a solenoid. It turns out that a changing external magnetic field causes an induced current in the coil, which, in turn, creates its own magnetic field around the coil - the current field.

Studying this phenomenon, E. H. Lenz established a law that determines the direction of the induced current in the coil, and therefore the direction of the induced emf. The induced emf that occurs in a coil when the magnetic flux changes in it creates a current in the coil in such a direction that the magnetic flux of the coil created by this current prevents a change in the extraneous magnetic flux.

Lenz's law is valid for all cases of current induction in conductors, regardless of the shape of the conductors and the way in which a change in the external magnetic field is achieved.

When a permanent magnet moves relative to a wire coil connected to the terminals of a galvanometer, or when a coil moves relative to a magnet, an induced current occurs.

Induction currents in massive conductors

A changing magnetic flux is capable of inducing an emf not only in the turns of the coil, but also in massive metal conductors. Penetrating the thickness of a massive conductor, the magnetic flux induces an emf in it, creating induced currents. These so-called ones spread along a massive conductor and short-circuit in it.

The cores of transformers, magnetic circuits of various electrical machines and devices are precisely those massive conductors that are heated by the induction currents arising in them. This phenomenon is undesirable, therefore, to reduce the magnitude of induced currents, parts of electrical machines and transformer cores are not made massive, but consist of thin sheets, isolated from one another with paper or a layer of insulating varnish. Thanks to this, the path of propagation of eddy currents through the mass of the conductor is blocked.

But sometimes in practice eddy currents are also used as useful currents. For example, the work of so-called magnetic dampers of moving parts of electrical measuring instruments is based on the use of these currents.

Induction current is a current that occurs in a closed conductive circuit located in an alternating magnetic field. This current can occur in two cases. If there is a stationary circuit penetrated by a changing flux of magnetic induction. Or when a conducting circuit moves in a constant magnetic field, which also causes a change in the magnetic flux penetrating the circuit.

Figure 1 - A conductor moves in a constant magnetic field

The reason for the occurrence of induction current is the vortex electric field that is generated magnetic field. This electric field acts on free charges located in a conductor placed in this vortex electric field.

Figure 2 - vortex electric field

You can also find this definition. Induction current is an electric current that arises due to the action of electromagnetic induction. If you don’t delve into the intricacies of the law of electromagnetic induction, then in a nutshell it can be described as follows. Electromagnetic induction is the phenomenon of the occurrence of current in a conducting circuit under the influence of an alternating magnetic field.

Using this law, you can determine the magnitude of the induction current. Since it gives us the value of the EMF that occurs in the circuit under the influence of an alternating magnetic field.

Formula 1 - EMF of magnetic field induction.

As can be seen from formula 1, the magnitude of the induced emf, and therefore the induced current, depends on the rate of change of the magnetic flux penetrating the circuit. That is, the faster the magnetic flux changes, the greater the induction current can be obtained. In the case when we have a constant magnetic field in which the conducting circuit moves, the magnitude of the EMF will depend on the speed of movement of the circuit.

To determine the direction of the induction current, Lenz's rule is used. Which states that the induced current is directed towards the current that caused it. Hence the minus sign in the formula for determining the induced emf.

Induction current plays important role in modern electrical engineering. For example, the induced current arising in the rotor asynchronous motor, interacts with the current supplied from the power source in its stator, as a result of which the rotor rotates. Modern electric motors are built on this principle.

Figure 3 - asynchronous motor.

In a transformer, the induction current arising in the secondary winding is used to power various electrical devices. The magnitude of this current can be set by the transformer parameters.

Figure 4 - electrical transformer.

And finally, induced currents can also arise in massive conductors. These are the so-called Foucault currents. Thanks to them, it is possible to perform induction melting of metals. That is, eddy currents flowing in the conductor cause it to heat up. Depending on the magnitude of these currents, the conductor can heat up above the melting point.

Figure 5 - induction melting metals

So, we have found that induction current can have mechanical, electrical and thermal effects. All these effects are widely used in modern world, both on an industrial scale and at the household level.

magnet. Mark which of the following statements are correct and which are incorrect.
A. The magnet and the coil attract each other.
B. Inside the coil, the magnetic field of the induction current is directed upward.
B. Inside the coil, the magnetic induction lines of the magnet's fields are directed upward.
D. The magnet is removed from the coil.

2. Which reference systems are inertial and non-inertial? Give examples.
3. What is the property of bodies called inertia? What value characterizes inertia?
4. What is the relationship between the masses of bodies and the acceleration modules that they receive during interaction?
5. What is strength and how is it characterized?
6. Formulation of Newton's 2nd law? What is its mathematical notation?
7. How is Newton’s 2nd law formulated in impulse form? Its mathematical notation?
8. What is 1 Newton?
9. How does a body move if a force is applied to it that is constant in magnitude and direction? What is the direction of the acceleration caused by the force acting on it?
10. How is the resultant of forces determined?
11. How is Newton’s 3rd law formulated and written?
12. How are the accelerations of interacting bodies directed?
13. Give examples of the manifestation of Newton’s 3rd law.
14. What are the limits of applicability of all Newton’s laws?
15. Why we can count the Earth inertial system reference point if it moves with centripetal acceleration?
16. What is deformation, what types of deformation do you know?
17. What force is called the elastic force? What is the nature of this force?
18. What are the features of elastic force?
19. How is the elastic force directed (support reaction force, thread tension force?)
20. How is Hooke’s law formulated and written? What are its limits of applicability? Construct a graph illustrating Hooke's law.
21. How the law is formulated and written Universal gravity when is it applicable?
22. Describe the experiments to determine the value of the gravitational constant?
23. What is the gravitational constant, what is it physical meaning?
24. Does the work done by the gravitational force depend on the shape of the trajectory? What is the work done by gravity in a closed loop?
25. Does the work of the elastic force depend on the shape of the trajectory?
26. What do you know about gravity?
27. How is acceleration calculated? free fall on Earth and other planets?
28. What is the first escape velocity? How is it calculated?
29. What is called free fall? Does the acceleration of gravity depend on the mass of the body?
30. Describe the experience Galileo Galilei, proving that all bodies in a vacuum fall with the same acceleration.
31. What force is called the friction force? Types of friction forces?
32. How are the forces of sliding and rolling friction calculated?
33. When does the static friction force occur? What is it equal to?
34. Does the force of sliding friction depend on the area of ​​contacting surfaces?
35. On what parameters does the sliding friction force depend?
36. What does the force of resistance to body motion in liquids and gases depend on?
37. What is body weight called? What is the difference between the weight of a body and the force of gravity acting on the body?
38. In what case is the weight of a body numerically equal to the modulus of gravity?
39. What is weightlessness? What is overload?
40. How to calculate the weight of a body during its accelerated movement? Does the weight of a body change if it moves along a stationary horizontal plane with acceleration?
41. How does the weight of a body change when it moves along a convex and concave part of a circle?
42. What is the algorithm for solving problems when a body moves under the influence of several forces?
43. What force is called the Archimedes Force or buoyant force? What parameters does this force depend on?
44. What formulas can be used to calculate the Archimedes force?
45. Under what conditions does a body in a liquid float, sink, or float?
46. ​​How does the depth of immersion of a floating body in liquid depend on its density?
47. Why Balloons filled with hydrogen, helium or hot air?
48. Explain the influence of the rotation of the Earth around its axis on the value of the acceleration of gravity.
49. How does the value of gravity change when: a) the body moves away from the surface of the Earth, B) when the body moves along the meridian, parallel

electrical circuit?

3. What is the physical meaning of EMF? Define volt.

4. Connect to a short time voltmeter source electrical energy, observing polarity. Compare its readings with the calculation based on the experimental results.

5. What does the voltage at the terminals of current sources depend on?

6. Using the measurement results, determine the voltage on the external circuit (if the work is performed using method I), the resistance of the external circuit (if the work is performed using method II).

6 question in attachment calculation

1. Under what conditions do friction forces appear?
2. What determine the modulus and direction of the static friction force?
3. Within what limits can the static friction force vary?
4. What force imparts acceleration to a car or diesel locomotive?
5. Can sliding friction force increase the speed of a body?
6. What is the main difference between the resistance force in liquids and gases and the friction force between two solids?
7. Give examples of the beneficial and harmful effects of friction forces of all types