What is equal to emf self-induction. What is self-induction - an explanation of simple words

Electric current passing through the conductor creates a magnetic field around it. The magnetic flow F through the contour from this conductor is proportional to the induction module in the magnetic field inside the contour, and the induction of the magnetic field in turn is proportional to the current power in the conductor. Consequently, the magnetic flux through the contour is directly proportional to the strength of the current in the circuit:

The proportionality coefficient between current strength I in the circuit and the magnetic flow F, created by this current, is called inductance. Inductance depends on the size and shape of the conductor, from the magnetic properties of the medium in which the conductor is located.

Unit of inductance.

For the unit of inductance in the international system, Henry adopted this unit is determined on the basis of formula (55.1):

The inductance of the contour is equal to if the power of DC is 1 A magnetic flux through the contour is equal

Self-induction.

When changing the current strength in the coil, a magnetic flux created by this current is changed. The change in the magnetic flux that pierces the coil should cause the appearance of an induction EMF in the coil. Phenomenon of EMF induction in

the electrical circuit as a result of a change in current in this chain is called self-induction.

In accordance with the rule of Lenz, self-induction is preventing the increase in current strength when the current force is turned on and descending when the chain is turned off.

The self-induction phenomenon can be observed by collecting the electrical circuit of the coil with a large inductance, a resistor, two identical incandescent lamps and a current source (Fig. 197). The resistor should have the same electrical resistance as the coil wire. Experience shows that when the electric LGGMP circuit is closed, enabled sequentially with the coil, lights up slightly later than the lamp included in sequentially with the resistor. Current increases in the circuit of the coil during a closure prevents self-induction EMF, which occurs with an increase in the magnetic flux in the coil. When the current source is disconnected, both lamps flas out. In this case, the current in the chain is supported by self-induction EMP, which occurs when the magnetic flux is descending in the coil.

EMF of self-induction arising in the coil with inductance under the law of electromagnetic induction is equal to

EMF of self-induction is directly proportional to the inductance of the coil and the speed of change of current in the coil.

Using expression (55.3), it is possible to give the second definition unit of inductance: the element of the electrical circuit has inductance in if with a uniform change in the current force in the chain by 1 and for 1 s in it there is a self-induction of 1 V.

Magnetic field energy.

When the inductor is disconnected from the current source of the incandescent lamp, turned on parallel to the coil, gives a short-term flash. The current in the chain occurs under the action of self-induction EMF. The source of energy highlighted in the electrical circuit is the magnetic field of the coil.

The energy of the magnetic field of the inductance coil can be calculated in the following way. To simplify the calculation, we consider this case when after disconnecting the coil from the source of the current in the chain decreases with time according to the linear law. In this case, self-induction EMF has a constant value equal to

At this lesson, we learn how and whose self-induction was opened, consider experience with which we will demonstrate this phenomenon, we define that self-induction is a special case of electromagnetic induction. At the end of the lesson, we introduce a physical value showing the dependence of self-induction EMF from the size and shape of the conductor and on the environment in which the conductor is located, i.e. inductance.

Henry was present to the flat coils from strip copper, with the help of which the power effects were sought, severely pronounced than using wire solenoids. The scientist noticed that when in the chain of a powerful coil, the current in this chain reaches its maximum value much slower than without coil.

Fig. 2. Scheme of experimental installation D. Henry

In fig. 2 shows the electrical circuit of the experimental installation, on the basis of which you can demonstrate the phenomenon of self-induction. The electrical circuit consists of two parallel connected light bulbs connected via the key to the DC source. A coil is connected from one of the light bulbs. After the circuit is closed, it can be seen that the light bulb that is connected in series with the coil, lights up more slowly than the second light bulb (Fig. 3).

Fig. 3. Different lighting light bulbs at the time of the circuit

When the source is disconnected, the light connected sequentially with the coil, goes out slower than the second light bulb.

Why light bulbs are not hooked at the same time

When the key is closed (Fig. 4), due to the occurrence of emf self-induction, the current in the light bulb with the coil is growing slower, so this light bulb lights up slower.

Fig. 4. Closing the key

When opening the key (Fig. 5), the emission of self-induction interferes with decreasing current. Therefore, the current continues to flow for some time. For current existence, a closed loop is needed. There is such an outline in the chain, it contains both light bulbs. Therefore, when the circuit is blurred, the light bulb should have the same one time, and the observed delay can be caused by other reasons.

Fig. 5. Blurring the key

Consider the processes occurring in this chain when closing and opening the key.

1. Closing the key.

The circuit contains a conductive coil. Let the current in this twist flow flowing counterclockwise. Then the magnetic field will be directed upward (Fig. 6).

Thus, the turn turns out to be in the space of its own magnetic field. As an increase in the current, the turn will be in the space of a changing magnetic field of the eigencurrent. If the current increases, then the magnetic flux created by this current also increases. As is known, with an increase in the magnetic flux, permeating the circuit plane, the electromotive force of induction occurs in this circuit and, as a result, the induction current. According to the rulers rule, this current will be directed in such a way that its magnetic field is preventing the change in the magnetic flux, which permeates the contour plane.

That is, for the figured in fig. 6 turns The induction current should be sent clockwise (Fig. 7), thereby preventing the increase in the roller's own current. Therefore, when closing the key, the current in the chain increases not instantly due to the fact that in this chain there is a braking induction current directed in the opposite direction.

2. Blurring the key

When operating the key, the current in the chain decreases, which leads to a decrease in the magnetic flux through the plane of the turn. Reducing the magnetic flux leads to the appearance of induction and induction current. In this case, the induction current is directed to the same side as its own current of the turn. This leads to a slowdown in its own current.

Output:when the current changes in the conductor, electromagnetic induction appears in the same conductor, which generates the induction current, directed in such a way as to prevent any change in its own current in the conductor (Fig. 8). This is the essence of self-induction. Self-induction is a special case of electromagnetic induction.

Fig. 8. The moment of turning on and off the chain

Formula for finding magnetic induction of direct conductor with current:

where - magnetic induction; - magnetic constant; - current strength; - Distance from the conductor to the point.

The flow of magnetic induction through the platform is:

where is the surface area that is permeated with a magnetic flux.

Thus, the flow of magnetic induction is proportional to the value of the current in the explorer.

For a coil, in which - the number of turns, and the length, the induction of the magnetic field is determined by the following ratio:

Magnetic stream created by a coil with a number of turns N.equal to:

Substituting a magnetic field induction formula in this expression, we get:

The ratio of the number of turns to the coil length is denoted by the number:

We obtain the final expression for the magnetic flux:

From the resulting relation, it can be seen that the value of the stream depends on the current value and the geometry of the coil (radius, length, number of turns). The value equal is called inductance:

Unit of inductance is Henry:

Consequently, the flow of magnetic induction caused by a current in the coil is:

Taking into account the formula for EDS induction, we obtain that self-induction EMF is equal to the product of the speed of change in the inductance taken with the "-" sign:

Self-induction - This is the appearance of electromagnetic induction in the conductor when the current flow changes through this conductor.

Electrical power of self-induction Directly proportional to the rate of change of current flowing through the conductor taken with the minus sign. The ratio of proportionality is called inductancewhich depends on the geometric parameters of the conductor.

The conductor has an inductance equal to 1 GN, if at a speed of current changes in the conductor, equal to 1 A per second, the electromotive power of self-induction occurs in this conductor, equal to 1 V.

With the phenomenon of self-induction, a person faces daily. Each time, including or turning off the light, we are thus closed or blurring the chain, while exciting induction currents. Sometimes these currents can reach such large values \u200b\u200bthat inside the switch sparks the spark that we can see.

Bibliography

Myakyshev G.Ya. Physics: studies. for 11 cl. general education. institutions. - M.: Enlightenment, 2010.
Kasyanov V.A. Physics. 11 CL: student. For general education. institutions. - M.: Drop, 2005.
Gentendestein L.E., Dick Yu.I., Physics 11. - M.: Mnemozin.

Internet portal Myshared.ru ().
Internet portal Physics.ru ().
Internet portal Festival 1September.ru ().

Homework

Questions at the end of paragraph 15 (p. 45) - Myakyshev G.Ya. Physics 11 (see the list of recommended literature)
Inductance What conductor is 1 Henry?

This phenomenon is called self-induction. (The concept is known to the concept of mutually induction, being as if its private case).

The direction of self-induccous EMF always turns out to be such that, with an increase in current in the EMF chain, self-induction prevents this increase (directed against the current), and when decreasing current - descending (coated with current). This property of self-induction EMF is similar to the power of inertia.

The magnitude of self-induction EMF is proportional to the speed of change of current:

The ratio of proportionality is called self-induction coefficient or inductance Contour (coil).

Self-induction and sinusoidal current

In the case of a sinusoidal dependence of the current flowing through the coil, from time to time, the self-induction emfs in the coil lags behind the current on the phase (that is, 90 °), and the amplitude of this EDC is proportional to the amplitude of the current, frequency and inductance (). After all, the rate of change of function is its first derivative, but.

To calculate more or less complex circuits containing inductive elements, that is, the turns, coils of the device, in which self-induction is observed, (especially completely linear, that is, not containing nonlinear elements) in the case of sinusoidal currents and stresses use the method of integrated impedances or, In simpler cases, less powerful, but a more visual version - method of vector diagrams.

Note that everything described applies not only directly to sinusoidal currents and stresses, but also almost arbitrary, since the latter can be almost always laid out in a row or the Fourier integral and thus reduced to sinusoidal.

In a more or less direct connection with this, it is possible to mention the use of the phenomenon of self-induction (and, respectively, inductance coils) in a variety of oscillatory circuits, filters, delay lines and other various electronics and electrical engineering schemes.

Self-induction and current jump

Due to the self-induction phenomenon in the electrical circuit with the source of the EMF, when the circuit circuit is closed, the current is not installed instantly, but after a while. Similar processes occur when opening the chain, while (with a sharp opening), the value of self-induction can at this point, significantly exceed the source EMF.

Most often in ordinary life it is used in car ignition coils. A typical ignition voltage at a voltage of the supply battery 12B is 7-25 square meters. However, the excess of the EDC in the output circuit above the EDC of the battery is due not only to the sharp interruption of the current, but also the transformation coefficient, since it is most often used not a simple inductor coil, and a transformer coil, a secondary winding of which as a rule has many times more turns ( That is, in most cases the scheme is somewhat more complex than the one, the work of which would be fully explained through self-induction; however, physics of its work and in this version partly coincides with the physics of the scheme with a simple coil).

This phenomenon is used for the ignition of luminescent lamps in the standard traditional scheme (here it is about the scheme with a simple inductor inductance - choke).

In addition, it should always be taken into account when the contacts are blurred if the current flows on the load with a noticeable inductance: the occurrence of the EMF leap can lead to a breakdown of the intertek intertension and / or other undesirable effects, for the suppression of which in this case, as a rule, it is necessary to take a variety of special measures.

Notes

Links

About self-induction and intention from "School for Electrician"

Wikimedia Foundation. 2010.

Watch what is "self-induction" in other dictionaries:

Self-induction ... Orphographic Dictionary

The occurrence of EMF induction in a conductive circuit when the current strength changes in it; Special cases of electromagnetic induction. When changing the current in the circuit, the flow of magn changes. induction through the surface limited to this circuit, resulting in ... Physical encyclopedia

Excitation of the electromotive force of induction (EDC) in the electrical circuit when the electric current changes in this chain; Private case of electromagnetic induction. The electromotive power of self-induction is directly proportional to the speed of change of current; ... ... Big Encyclopedic Dictionary

Self-induction, self-induction, wives. (Piz.). 1. Only units. The phenomenon that consists in the fact that when the current changes the current, then there appears an electromotive force that impede this change. Self-induction coil. 2. Device with ... ... Explanatory Dictionary Ushakov

- (Self Induction) 1. A device with inductive resistance. 2. The phenomenon consistent that when an electric current changes in the conductor in magnitude and in the direction, then there is an electromotive force that impede this ... ... ...

Hovering the electromotive force in the wires, as well as in the windings of electrical. machines, transformers, apparatuses and devices when changing the value or direction of electrical electrical. Current. The current flowing on the wires and windings creates around them ... ... Technical Railway Dictionary

Self-induction - electromagnetic induction caused by a change in the adhesive with a magnetic flux circuit due to electric shock in this circuit ... Source: Electrical Engineering. Terms and definitions of basic concepts. GOST R 52002 2003 (appliance ... ... Official terminology

SUT., Number of synonyms: 1 Excitation of the electromotive force (1) Dictionary of Synonyms ASIS. V.N. Trishin. 2013 ... Synonym dictionary

self-induction - electromagnetic induction caused by a change in the magnetic flux with a magnetic flow circuit due to the electric shock in this circuit. [GOST R 52002 2003] EN SELF INDUCTION ELECTROMAGNETIC INDUCTION IN A TUBE OF CURRENT DUE TO VARIATIONS ... Technical translator directory

Self-induction - a special case of electromagnetic induction (see (2)), consisting in the occurrence of an induced (induced) EMF in the chain and caused by changes in the time of the magnetic field created by the current current flowing in the same chain. ... ... Large polytechnic encyclopedia

Books

Set of tables. Physics. Electrodynamics (10 tables) ,. An academic album of 10 sheets. Electric current, current. Resistance. Ohm law for the chain section. The dependence of the resistance of the conductor on temperature. Wire connection. EMF. Ohm's law…

Self-induction

Each conductor for which El.tok flows is in its own magnetic field.

When the current change in the conductor changes M. POLE, i.e. The magnetic flux created by this current changes. The change in the magnetic flux leads in the occurrence of vortex email and in the circuit appears induction.

This phenomenon is called self-induction.

Self-induction - the phenomenon of the occurrence of EMF induction in an email fall as a result of a change in the current force.
The emerging EMF is called EMF self-induction

Manifestation of the phenomenon of self-induction

Circuit chain

When the current increases in an email, which causes an increase in magnetic flux in the coil, a vortex email appears against the current, that is, in the coil, self-induction EMPs occurs, which prevents the increase in current in the chain (the vortex field slows down the electrons).
As a result, L1 lights up later than L2.

Blurring chain

When operating an email deck decreases, a decrease in M.Potok in the coil arises, the vortex email appears, directed as the current (striving to preserve the former current strength), i.e. In the coil there is a self-induction EMF, which maintains the current in the chain.
As a result, when it turns off brightly flashes.

In the electrical engineering, the self-induction phenomenon is manifested when the circuit is closed (the electric current is growing gradually) and when the circuit is blurred (the electric current does not disappear).

INDUCTANCE

What does emd self-induction depend on?

Electric current creates its own magnetic field. Magnetic flow through the contour is proportional to the induction of the magnetic field (F ~ B), the induction is proportional to the current power in the conductor
(B ~ i), therefore, the magnetic flow is proportional to the strength of the current (F ~ I).
EMF of self-induction depends on the rate of change in the current of the current in the email, from the properties of the conductor (sizes and shapes) and on the relative magnetic permeability of the medium in which the conductor is located.
The physical value showing the dependence of self-induction EMF from the size and shape of the conductor and on the medium in which the conductor is called the self-induction coefficient or inductance.

Inductance is a physical quantity, numerically equal to self-induction EMF, which occurs in the circuit when the current changes by 1 per 1 second.
Also inductance can be calculated by the formula:

where F is a magnetic flow through the contour, I is the current strength in the circuit.

Units of inductance in the SI system:

The inductance of the coil depends on:
The number of turns, sizes and shape of the coil and on the relative magnetic permeability of the medium (core is possible).

EMF self-induction

EMF of self-induction prevents the increase in current force when the circuit is turned on and decreasing the current for the circuit of the chain.

Magnetic current energy

Around the conductor with current there is a magnetic field that has energy.
Where does she come from? The current source included in the email has a reserve of energy.
At the time of the circuit of the email deck, the current source consumes part of its energy to overcoming the action of the self-induction that occurs. This part of the energy called its own current energy, and goes to the formation of a magnetic field.

The magnetic field energy is equal to the current current.
Own current current is numerically equal to the work that the current source must perform to overcome self-induction EMF to create a current in the chain.

The energy of the magnetic field created by the current is directly proportional to the square of the current force.
Where does the magnetic field energy disappear after the current stop? - It is allocated (when operating a chain with a sufficiently large strength of current, a spark or arc may occur)

Questions for verification work

on the topic "Electromagnetic induction"

1. List 6 methods for producing induction current.
2. Phenomenon of electromagnetic induction (definition).
3. Lenza rule.
4. Magnetic stream (definition, drawing, formula incoming values, their units. Measurements).
5. The law of electromagnetic induction (definition, formula).
6. Properties of the vortex electric field.
7. EMF induction of a conductor moving in a homogeneous magnetic field (reason for the appearance, drawing, formula, incoming values, their units. Measurements).
8. Impropation (briefly manifest in electrical engineering, definition).
9. EMF of selfinducia (its action and formula).
10. Inductance (definition, formula, units. Measurements).
11. Energy of the magnetic field of the current (formula, from where the energy of the m. The current fields where the current is lost during the ceases).