Slide into the short-circuited coil. When a magnet is pushed inside a short-circuited wire coil. Reshebnik in physics L.A. Kirik Independent and control works

Is electromagnetic induction so familiar to you? // Quant. - 1989. - No. 6. - S. 40-41.

By special agreement with the editorial board and editors of the Kvant magazine

Hope to get electricity with
ordinary magnetism at different times
encouraged me to experimentally study
inductive action of electric currents.
M. Faraday

Faraday devoted his entire life to proving that no electrical or magnetic process occurring in nature proceeds in isolation. Faraday's deep faith in the interconnection of all the forces of nature led him, after many years of failure, to a unique discovery.

The new effect, as often happens, was then found in a multitude of seemingly different phenomena, united, however, by one qualitative conclusion: alternating magnetic fields excite electric fields. It is on this principle that the operation of all existing electrical machines is based. It was Faraday's discovery that made it possible to convert mechanical energy into electrical energy, transfer energy to a distance, and thus laid the foundation for modern technical civilization.

The works of Faraday and his outstanding contemporaries allowed to create, step by step, a unified picture of electromagnetism.

When studying this section of physics, you will not only explain the facts and observations known to you, but will also be able to deal with electromagnetic phenomena of both cosmic and microscopic scales.

Questions and tasks

How to move the magnet to turn the arrow with the north pole towards the observer?
The horizontal circular frame is in a magnetic field directed vertically upward. What will be the direction of the induction current when observing the frame from above if the field decreases with time?
At what positions of the frame rotating at a constant speed for a straight conductor with current, the EMF arising in it will be the greatest? the smallest?
A magnet is pushed into the short-circuited coil at first quickly and then slowly. Is the same charge carried by the induction current? Does the coil generate the same amount of heat?
How will a magnet fall in a long copper tube? Neglect air resistance.
The ends of the doubled wire are attached to the galvanometer. Why does the arrow of the device remain at zero when the wire crosses the induction lines magnetic field?
There is a metal coin on a vertical spool. Why does it heat up when alternating current flows through the coil, and remains cold when constant?
A current flows through a straight conductor high frequency... How will the resistance of this conductor change if it is given the shape of a solenoid?
Conductor AB moves in such a way that current flows through it from the point A to the point V... At which of these points is the potential higher?
Two identical planes fly horizontally at the same speeds, one near the equator, the other near the pole. Which of them has a large potential difference at the ends of the wings?
The rotor of a running generator is braked. What is the nature of the forces causing this inhibition?
The two circular conductors are perpendicular to each other. Will there be induction current in the conductor A with changes in the current in the circuit V?
A superconducting ring is located near a permanent magnet and is penetrated by a magnetic flux F. There is no current in the ring. What will be the magnetic flux through this ring if you remove the magnet?

Microexperience

Hang a horseshoe magnet on a string over an aluminum foil disk that can rotate about an axis through its center. If you unscrew the magnet, the disc will start to rotate. Which way. Why?

It is curious that ...

Newer types of electrical machines do not have any mechanical moving parts. In the so-called MHD (magnetohydrodynamic) generator, instead of a wire conductor between the poles of the magnet, the plasma moves, formed during the combustion of oil or gas. The charge carriers in the plasma are deflected by the magnetic field towards the electrodes, and a current arises in the external circuit.

Faraday carried a small strip magnet and wire spool in his vest pocket for years as a constant reminder of the unsolved problem of generating electric current by a magnetic field.

Eddy induction currents (Foucault currents) can, like friction, be not only harmful, but also useful. Just three examples: induction furnaces for heating and even melting metals, "magnetic damping" in measuring instruments and circular saws and ... well-known electric energy meter.

Having independently come to the idea of electromagnetic rotation, Faraday, using a mercury contact, carried out a continuous rotation of a magnet around a conductor with a current. This first electric motor started operating in December 1821.

Lenz's rule, which determines the direction of the induction current, was formulated almost immediately after the discovery of Faraday - in 1833. Today, a vivid manifestation of this rule can be observed in school laboratory by placing a superconducting ceramic tablet over a magnet: it will "hover" over it.

What to read in "Quantum" about electromagnetic induction

"Electromagnetic induction and the principle of relativity" - 1987, No. 11;
"Ways of Electromagnetic Theory" - 1988, No. 2;
Lenz's Rule - 1988, No. 5;
"Superconductivity: history, modern ideas, recent successes" - 1988, no. 6;
"The Lorentz Force and the Hall Effect" - 1989, no. 3.

Answers

Slide into the spool.
Counterclock-wise.
EMF of induction will have the smallest value when the frame is in the plane passing through the wire, the largest - when the frame is perpendicular to this plane.
No, since the flux of the magnetic induction of the circuit V does not penetrate the contour A.
Same. No, because the amount of heat is proportional to the speed of the magnet.
When the magnet moves in the tube, an EMF of induction arises, which generates a magnetic field that prevents the free fall of the magnet.
Along with the usual friction, the rotor and the ampere forces acting on it from the side of the stator magnetic field slow down.
An airplane flying near the pole.
In the two halves of the wire, induction EMFs of equal magnitude, but opposite in sign, appear, which are mutually compensated.
At the point V, since on the site ICA, where there are no sources of EMF, the current goes from V To A.
With an alternating current, eddy currents appear in the coin, with a constant current, no.
Will increase.
Since the resistance of the ring is zero, then the total EMF in it must always be zero. This can only be the case if the change in the total magnetic flux through the ring is zero. Consequently, when the magnet is removed, the magnetic flux created by the induction current will remain equal to F.

Microexperience

The alternating magnetic field of a rotating magnet excites induction eddy currents in the disk, directed so that the magnetic field they create inhibits the movement of the magnet. According to Newton's third law, an equal and oppositely directed force acts on the disk and drags it along after the magnet.

I 1 >I 2

In a magnetic field with induction VF

Emr

is the same along all trajectories

The following was observed in Ampere's experiment

interaction of two parallel conductors with current

In Oersted's experiment, the following was observed

rotation of a magnetic needle near a conductor when a current is passed through it

In the circuit shown in the figure, the rheostat slider is moved up. In this case, the readings

ammeter increased, voltmeter decreased

In a cyclotron, as the velocity of a charged particle doubles, its orbital period (Consider the nonrelativistic case ( vc))

Will not change

The vector of the electric field strength at the point O, created by two charges of the same name, has the direction

The vector of the electric field strength at the surface of the conductor with current is shown correctly in the figure

The current-voltage characteristic of the vacuum diode corresponds to the graph

The current-voltage characteristic of the gas discharge is more consistent with the graph

The current-voltage characteristic of the filament of the incandescent lamp corresponds to the graph

The expression for the modulus of the Ampere force corresponds to the formula

F=IBl sin

The expression for the modulus of the Lorentz force corresponds to the formula

F=qvB sin

The expression for the current in the conductor corresponds to the formula

High voltage required to discharge (s)

spark

The graph of the dependence of the resistance of the conductor on temperature corresponds to the graph

Two identical sources with EMF are each connected in parallel. Readings from a voltmeter connected to points 1 and 2

Two resistors having resistances R 1 = 3 ohms and R 2 = 6 Ohm, connected in series in the circuit direct current... Compare works A electric current across these resistors for the same time

A 2 = 2A 1

The unit of inductance is called

The unit of magnetic flux is called

The unit of magnetic induction is called

The EMF unit is called

From the following statements: 1) the magnetic field is generated by moving charges and an alternating electric field (displacement current); 2) an electric field with closed lines of force (vortex field) is generated by an alternating magnetic field; 3) the lines of force of the magnetic field are always closed (this means that it has no sources - magnetic charges, similar to electric ones); 4) an electric field with open lines of force (potential field) is generated by electric charges - the sources of this field - the second corresponds to Maxwell's equation

A drop with a positive charge + e lost one electron under illumination. The drop charge has become

The wire frame is in a uniform magnetic field. Electric current in it arises when: 1) the frame is moved along the lines of induction of the magnetic field; 2) the frame is moved across the magnetic induction lines; 3) the frame is turned around one of its sides

The wire frame is pushed into a uniform magnetic field (as shown in the figure) In this case, the induction current

directed I - clockwise, II - zero, III - counterclockwise

The physical quantity determined by the work done by the total field of electrostatic (Coulomb) and external forces when a single positive charge moves in a given section of the circuit is called

tension

A permanent magnet is inserted into the short-circuited coil: once quickly, the second time slowly Compare the values of the induction current arising from this

I 1 >I 2

In a magnetic field with induction V= 4 T, an electron moves at a speed of 10 7 m / s, directed perpendicular to the lines of induction of the magnetic field. Power module F acting on the electron from the side of the magnetic field is

In a uniform electric field of strength E= 2 10 3 V / m, a charged particle (q = 10 -5 C) with a mass m= 1 g. When passing a distance r= 10 cm the particle acquires speed

In a uniform electric field, a positive charge moves from point 1 to point 2 along different paths. The work of the forces of the electric field

is the same along all trajectories

Physics Test Phenomenon electromagnetic induction for grade 11 with answers. The test includes 2 options. Each version has 5 tasks.

Option 1

1. v in a uniform magnetic field as shown in Figure 35. What charges are formed at the edges of the rod?

A. 1 - negative, 2 - positive.
B. 1 - positive, 2 - negative.

2. The magnet is introduced into the short-circuited coil the first time quickly, the second time slowly. In which case is the charge carried by the induction current greater?

A. In the first case, the charge is greater.
B. In the second case, the charge is greater.
B. In both cases, the charges are the same.

3. In a magnetic field with an induction of 0.25 T perpendicular to the lines of induction at a speed of 5 m / s, a conductor 2 m long moves. What is the EMF of induction in the conductor?

A. 250 V.
B. 2.5 C.
V. 0.4 V.

4. In 3 s, the magnetic flux penetrating the wire frame steadily increased from 6 Wb to 9 Wb. What is the value of the induction EMF in the frame in this case?

A. 1 B.
B. 3 C.
B. 6 C.

5. At what direction of motion of the circuit in a magnetic field (Fig. 36) does an induction current arise in it?

A. When moving in the plane of the drawing to the right.
B. When moving in the plane of the drawing from us.
AB.

Option 2

1. The metal rod moves at a speed v in a uniform magnetic field as shown in Figure 37. What charges are formed at the edges of the rod?

A. 1 - negative, 2 - positive.
B. 1 - positive, 2 - negative.
Q. No definite answer can be given.

2. The magnet is introduced into the short-circuited coil the first time quickly, the second time slowly. In which case is the work done by the emerging EMF greater?

A. In the first case, the work is more.
B. In the second case, the work is more.
Q. In both cases, the work is the same.

3. In a magnetic field with an induction of 0.5 T l perpendicular to the induction lines at a speed of 4 m / s, a conductor 0.5 m long moves. What is the EMF of induction in the conductor?

A. 100 V.
B. 10 C.
B. 1 B.

4. In 2 s, the magnetic flux penetrating the wire frame decreased evenly from 9 Wb to 3 Wb. What is the value of the EMF of induction in the frame in this case?

A. 4 B.
B. 3 C.
B. 2 C.

5. At what direction of movement of the circuit in a magnetic field (Fig. 38) does an induction current arise in it?

A. When moving the plane of the drawing to the right.
B. When the plane of the drawing moves away from us.
B. When turning around the side BD.

Answers to the physics test Phenomenon of electromagnetic induction for grade 11
Option 1
1-B
2-B
3-B
4-A
5-B
Option 2
1-B
2-A
3-B
4-B
5-B

When a magnet is pushed inside a short-circuited wire coil, an induction current is generated in the coil. Choose the correct statement.
A. Lines of magnetic induction of the field of the magnet enter its north pole.

B. Magnet and coil are repelled from each other.

B. Inside the coil, the magnetic field of the induction current is upward.

D. Induction current flows counterclockwise in the coil (viewed from above).

Reshebnik in physics L.A. Kirik Independent and control works

1. The figure shows the magnetic lines of a straight conductor with current. Choose the correct statement.
A. For the direction of the magnetic line at a given point, take the direction that indicates the south pole of the magnetic needle placed at this point.
B. To find the direction of the magnetic lines, you can use the rule right hand.
B. Magnetic lines are shorted only in the vicinity of a straight current conductor.
D. The direction of the magnetic lines does not depend on the direction of the current in the conductor.

2. When a short-circuited wire coil is put on a stationary magnet, an induction current is generated in the coil. Choose the correct statement.

A. The number of magnetic lines piercing the coil does not change in this experiment.
B. The direction of the induction current is independent of whether the coil is put on the north or south pole of the magnet.
B. The phenomenon of electromagnetic induction is associated with the occurrence of a current in the circuit under the influence of a changing magnetic field.
D. If you remove the coil from the magnet, the direction of the induction current in the coil will not change.

3. Between the poles of a strong electromagnet, a ring made of copper wire is quickly rotated. This heats up the ring. Explain why this is happening.

When a closed loop of a conductor rotates in a constant magnetic field, the magnetic flux through this loop will change. When the magnetic flux changes according to Faraday's law, the EMF of induction will occur. Since the circuit is closed, an induction current will flow in it, which will have a thermal effect.

4. What work did you do in the conductor electricity, if the charge passed through the circuit is 1.5 C, and the voltage at the ends of this conductor is 6 V?

5. An electric boiler with a 160 Ohm spiral is placed in a vessel containing 0.5 kg of water at 20 ° C, and is connected to a 220 V network. After 20 minutes, the boiler was turned off. How much water has boiled away if the spiral efficiency is 80%?

To observe the phenomenon of electromagnetic induction, an electrical circuit is assembled, which includes a movable wire coil connected to an ammeter and a stationary magnet. Induction current in the coil will appear

1) only if the coil is stationary relative to the magnet

2) only if the coil is put on a magnet

3) only if the coil is removed from the magnet

4) if the coil is put on a magnet or removed from a magnet

According to the law of electromagnetic induction, an induction current arises in the circuit when the magnetic flux through the circuit changes. In this case, it does not matter what the reason for the change is, it can be the movement of the magnet relative to the contour, or the movement of the contour relative to the magnet. It is also not important how the flux changes, whether it increases or decreases, this determines only the direction of the induction current. Since under the conditions of the problem the magnet is stationary, the induction current can be observed by putting the coil on the magnet or removing it from it. Statement 4 is true.

ELECTROMAGNETIC INDUCTION

Part A.

1. A permanent magnet is inserted into the short-circuited coil: once quickly, another time slowly. Compare the induction current values in these cases.

A. I 1 = I 2 = 0 B. I 1 = I 2 = 0 B. I 1> I 2. G. I 1 2

2. There are three identical metal rings. A magnet is removed from the first ring, a magnet is inserted into the second ring, a stationary magnet is located in the third ring. In which ring does the induction current flow?

3. A lightweight wire ring is suspended from a thread. When a magnet is pushed into the ring by the south pole, it will: 1) repel from the magnet; 2) be attracted to the magnet; 3) motionless; 4) first push off, then pull.

4. In 3 s, the magnetic flux penetrating the wire frame increased from 6 to 18 Wb. EMF of induction is equal to: 1) 2 V; 2) 4V;

3) 6V; 4) 8 V.

5. The magnetic flux Ф, penetrating the conducting contour of the wire frame, changes over time as shown in graph 1. In which case the current in the frame is maximum?

1) In all cases, the induction current is the same. 2) In the second. 3) In the third. 4) In the first.

6. With a uniform increase in current strength by 2 A for 4 s, an EMF of induction of 0.8 V appears in the coil. What is the inductance of the coil?

1) 0.1 G. 2) 0.4 G. 3) 1.6 G. 4) 6.4 G.

7. In fig. 2 shows an electrical diagram. Which of the bulbs in this circuit will light up later than all the others after the key is closed?

1) 1. 2) 2. 3) 3. 4) 4.

8. What is the value of the current in a coil with an inductance of 2 H, if the magnetic field energy of the coil is 16 J?

1) 2A. 2) 8A. 3) 4 A. 4) 2.2 A.

9. When the current in the coil decreases by 3 times, the energy of its magnetic field: 1) will increase by 9 times; 2) will decrease by 9 times; 3) will decrease by 3 times; 4) will increase by 3 times.

10. On a straight conductor 1.4 m long and with a resistance of 2 Ohm, located in a uniform magnetic field with an induction of 0.25 T, a force of 2.1 N acts. The voltage at the ends of the conductor is 24 V, the angle between the conductor and the direction of the induction vector is ___ degrees: 1) 90 °; 2) 60 °; 3) 45 °; 4) 30 °.

11. The question of the direction of the induction current in its most general form was first solved by: 1) Oersted; 2) Lenz; 3) Ampere; 4) Faraday.

12. Wire frame with an area of 100 square meters. cm is placed in a uniform magnetic field, the dependence of the induction of which is shown in graph 2. If the plane of the frame makes an angle of 30 with the direction of the magnetic induction lines, then at time t = 3s the EMF of induction acts on the frame, equal to:

1) 2mV; 2) 1mV; 3) 0.7 mV; 4) 0.3mV.

13. The main property of an induction electric field is: 1) the field is created by a changing magnetic field; 2) the field is created by a changing electric charge; 3) the lines of force of the induction field are always open; 4) the field is potential.

14. The unit of magnetic induction is:

1) Ampere; 2) Henry; 3) Weber; 4) Tesla.

Part B.

15. In a coil of 200 turns, the magnetic induction increases uniformly from 1 to 5 T in 0.1 s. Determine the EMF of induction arising in the coil if the area of the turns is 6 cm.

16. The inductance of the coil is 2 H, its current is 6 A. What is the EMF of self-induction in the coil if the current in it decreases uniformly to 0 in 0.05s?

17. What is the current in a 40 mH coil if the magnetic field energy is 0.18 J?

18. Suppose that a magnet is inserted into a superconductor ring. How will the magnetic flux passing through the ring change?

19. Explain the transformation of energy that occurs when you turn the magnetic needle near the wire through which the current was started.

(Give a detailed answer)