EMF induction arising in a direct conductor. E.D.S.

Or, on the contrary, the moving magnetic field crosses the fixed conductor; or when the conductor and the magnetic field, moving in space, move one relative to the other;

When an alternating magnetic field of one conductor, acting on another conductor, induce EMF in it (mutually induction);

When the changing magnetic field is induced by the EMF itself (self-induction).

Thus, any change in the time of the magnitude that penetrates a closed loop (the turn, frame) is accompanied by an induced EMF in the conductor.

A. = U. × I. × t. = I.² × r. × t. (J).

The power spent will be equal to:

P. EL \u003d U. × I. = I.² × r. (W),

from where we determine the current in the chain:

(1)

However, we know that the conductor with a current placed in a magnetic field will experience force on the side of the field aspiring to move in the direction determined by the rule of the left hand. With its movement, the conductor will cross the magnetic power lines of the field and in it, by the law of electromagnetic induction, induced EMF will arise. The direction of this EDC, determined by the rule of right hand, will be a quarter I.. Let's call her reverse EMF E. arr. Value E. OBR according to the law of electromagnetic induction will be equal to:

E. Obr \u003d. B. × l. × v. (IN) .

By closed circuit, we have:

U. - E. Obr \u003d. I. × r.

U. = E. Obr + I. × r. ,

(2)

where did the current in the chain

(3)

Comparing expressions (1) and (3), we see that in the conductor moving in a magnetic field, with the same values U. and r. The current will be less than with a fixed conductor.

Multiplying the resulting expression (2) on I.We will get:

U. × I. = E. Obr × I. + I.² × r. .

As E. Obr \u003d. B. × l. × v.T.

U. × I. = B. × l. × v. × I. + I.² × r. .

Considering that B. × l. × I. = F. and F. × v. = P. Fur, we have:

U. × I. = F. × v. + I.² × r.

P. = P. Fur +. P. Em.

The latter expression shows that when the conductor is moved with a current in a magnetic field, the power of the voltage source is converted into thermal and mechanical power.

When moving a straight line conductor in a magnetic field at the ends of the conductor arises e. d. s. induction. It can be calculated not only by the formula, but also by the formula E. d. s.

induction in a straight conductor. It is displayed like this. We equate formula (1) and (2) § 97:

BILS \u003d EIΔT, From here

where S / ΔT \u003d V There is a speed of moving the conductor. Therefore er d. s. Induction when driving conductor perpendicular to the power lines magnetic field

E \u003d BLV.

If the conductor moves at a speed V (Fig. 148, a) directed at an angle α to the induction lines, then the speed V decomposes into the components V 1 and V 2. The component is directed along the induction lines and when the conductor moves, it does not cause e. d. s. induction. In the conductor e. d. s. Industed only at the expense of the component v 2 \u003d V SIN αdirected perpendicular to induction lines. In this case, e. d. s. Induction will be

E \u003d CLV SIN α.

This is the formula E. d. s. Induction in a straight conductor.

So, when moving a straight line conductor in a magnetic field, it is induced e. d., whose value is directly proportional to the active length of the conductor and the normal component of its speed.

If instead of one direct conductor take the frame, then with its rotation in a homogeneous magnetic field it will arise. d. s. In her two sides (see Fig. 138). In this case, e. d. s. Induction will be E \u003d 2 BLV SIN α. Here L is the length of one active side of the frame. If the latter consists of N turns, it occurs in it. d. s. induction

E \u003d 2NBLV SIN α.

What e. d. s. Induction depends on the speed of V rotation of the frame and from induction in a magnetic field, can be seen at such an experiment (Fig. 148, b). With slow rotation anchor of the current generator, the light bulb is burning dimly: a small er d. s. induction. With an increase in the speed of rotation, the anchor light burns brighter: a large e is arise. d. s. induction. At the same speed of rotation, the anchors remove one of the magnets, thereby reducing the induction of the magnetic field. Light bulb burns dim: er d. s. Induction decreased.

Task 35. Straight conductor length 0.6 M. Flexible conductors are attached to the current source, er d. s. whom 24 B. and internal resistance 0.5 ohms. The conductor is in a homogeneous magnetic field with induction 0.8 T., The induction lines of which are directed to the reader (Fig. 149). Resistance to the entire external chain 2.5 Ohm.. Determine the strength of the current in the conductor, if it moves perpendicular to the induction lines at speeds 10 m / s. What is the current power in a fixed conductor?

The rectilinear conductor AV moves in a magnetic field with induction in conductive tires that are closed on the galvanometer.

On electrical charges, moving along with the conductor in a magnetic field, the Lorentz power acts:

FL \u003d / Q / VB SIN A

Its direction can be determined by the rule of the left hand.

Under the action of the power of Lorentz inside the conductor, the distribution of positive and negative charges along the entire length of the conductor L
Lorentz's strength is in this case a third-party force, and in the conductor there is an EDC induction, and at the ends of the conductor AV occurs the difference of potentials.

The cause of the occurrence of EMF induction in a moving conductor is explained by the action of Lorentz's strength on free charges.

Preparing for verification work!

1. With which direction of the contour movement in the magnetic field in the circuit will occur induction current?

2. Specify the direction of the induction current in the circuit when it is introduced into a homogeneous magnetic field.

3. How will the magnetic flux change in the frame if the frame is rotated 90 degrees from position 1 to position 2?

4. Will there be an induction current in conductors if they move as shown in the picture?

5. Determine the direction of induction current in an AB conductor moving in a homogeneous magnetic field.

6. Specify the correct direction of the induction current in the contours.

Electromagnetic field - Class! Naya Physics

EMF is an abbreviation of three words: electromotive force. EMF induction () appears in a conductive body, which is in a variable magnetic field. If a conductive body is, for example, a closed loop, an electric current flows, which is called induction current.

Faraday law for electromagnetic induction

The basic law, which is used in the calculations associated with electromagnetic induction is the law of Faraday. It suggests that the electromagnetic power of electromagnetic induction in the circuit is equal in size and is opposite to the sign of the rate of change of magnetic flux () through the surface that the contour underlined:

Faraday law (1) is recorded for SI system. It must be borne in mind that from the end of the vector normal to the contour, the contour bypass should be counterclockwise. If the change in the flow occurs evenly, then the induction is found as:

The magnetic stream that covers the conductive circuit may vary in connection with different reasons. This may be the time-changing magnetic field and the deformation of the contour itself, and move the contour in the field. The total derivative of the magnetic flux by time takes into account the effect of all reasons.

EMF induction in a moving conductor

Suppose that the conductive circuit moves in a constant magnetic field. EMF induction occurs in all parts of the contour, which intersect the power lines of the magnetic field. At the same time, the resulting EMF appears in the circuit will be equal to the algebraic amount of EMF of each site. The emergence of EDC in the case under consideration is explained by the fact that on any free charge, which moves along with the conductor in the magnetic field, the Lorentz power will be valid. When exposed to the Lorentz forces, charges move and form induction current in the closed conductor.

Consider the case when a rectangular conductive frame is located in a homogeneous magnetic field (Fig. 1). One side of the frame can move. The length of this side is equal to l. This will be our moving conductor. We define how to calculate the EDC induction, in our conductor, if it moves at a speed V. The magnetic field induction value is B. Frame plane perpendicular to magnetic induction vector. The condition is performed.

EMF induction in the circuit under consideration will be equal to EMF, which occurs only in its movable part. In the stationary parts of the contour in a constant magnetic field of induction.

To find EMF induction in the frame, we use the basic law (1). But for a start, we will define with a magnetic flux. By definition, the flow of magnetic induction is:

where, since the condition plane frame is perpendicular to the direction of the field induction vector, therefore, the normal to the frame and the induction vector is parallel. The area that limits the frame will express as follows:

where - the distance to which the moving conductor moves. We will substitute expression (2), taking into account (3) in the Faraday law, we get:

where V is the movement speed of the movable side of the frame on the X axis.

If the angle between the direction of the magnetic induction vector () and the velocity vector of the conductor () is an angle, the EDC module in the conductor can be calculated using the formula:

Examples of solving problems

Example 1.

The task

Get an expression to determine the EDC induction module in the conductor, long L, which moves in a homogeneous magnetic field using the expression for the Lorentz force. The conductor in Fig. 2 is moving at a constant speed, in parallel to itself. The vector is perpendicular to the conductor and makes an angle with the direction.

Decision

Consider the force with which the magnetic field acts on the charged particle moving at speed, we will get:

The work of Lorentz's power on the way L will be:

EMF induction can be defined as a job on the movement of a single positive charge:

Answer

Example 2.

The task	The change in the magnetic flux through the conductor circuit having the resistance of OM during the equal basis of C, was the value of the WB. What is the strength of the current at the same time in the conductor, if the change in the magnetic flux can be considered uniform?
Decision	With a uniform change of magnetic flux, the main law of electromagnetic induction can be written as:

The relationship of electrical and magnetic phenomena has always been interested in physicists. English physicist Michael Faraday It was quite confident in the unity of electrical and magnetic phenomena. He argued that the electric current is able to magnetize a piece of iron. Can a magnet in turn cause the appearance electric current? This task was solved.

If the conductor moves in a constant magnetic field, then the free electrical charges inside it are also moved (there is a Lorentz power). Positive charges are concentrated at one end of the conductor (wires), negative - in the other. There is a difference in potentials - EMF electromagnetic induction. The occurrence of EMF induction in the conductor moving in a constant magnetic field is called the phenomenon of electromagnetic induction.

Rule definition direction of induction current (Rule rule):

In the conductor moving in a magnetic field, an EDC induction occurs, current energy in this case is determined by the law of Joule-Lenza:

Work of external force to move the conductor with a current in a magnetic field

EMF induction in contour

Consider changing the magnetic flux through the conductive circuit (coil). The phenomenon of electromagnetic induction was opened by experimental way:

Electromagnetic Induction Act (Faraday Law): EMF electromagnetic induction arising in the circuit is directly proportional to the rate of change of magnetic flux through it.