When a magnet is pushed inside a short-circuited wire coil. When the magnet is pushed inside a short-circuited wire coil High voltage is required for the discharge(s)

Physics test The phenomenon of electromagnetic induction for grade 11 with answers. The test includes 2 options. Each option has 5 tasks.

1 option

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. A 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, a conductor 2 m long moves perpendicular to the lines of induction at a speed of 5 m / s. What is the EMF of induction in the conductor?

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

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

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

5. In what direction of movement of the circuit in a magnetic field (Fig. 36) does an induction current appear in it?

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

Option 2

1. A metal rod is moving 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.
B. A definite answer cannot be given.

2. A 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.
B. In both cases, the work is the same.

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

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

4. For 2 s, the magnetic flux penetrating the wire frame decreased uniformly from 9 Wb to 3 Wb. What is the value of the induction emf in the frame?

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

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

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

Answers to the test in physics The phenomenon of electromagnetic induction for grade 11
1 option
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. The lines of magnetic induction of the field of a magnet enter its north pole.

B. Magnet and coil repel each other.

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

D. The induction current is directed counterclockwise in the coil (when viewed from above).

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

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 direction magnetic lines, you can use the rule right hand.
B. Magnetic lines are closed only near a straight conductor with current.
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 penetrating the coil does not change in this experiment.
B. The direction of the induction current does not depend on 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 current in the circuit under the influence of a changing magnetic field.
D. If you remove the coil from the magnet, then the direction of the induction current in the coil will not change.

3. A ring made of copper wire is rapidly rotated between the poles of a strong electromagnet. This heats up the ring. Explain why this is happening.

When a closed loop rotates from a conductor in a constant magnetic field, the magnetic flux through this loop will change. When the magnetic flux changes according to Faraday's law, an 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 explorer electricity if the charge that has 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 spiral resistance of 160 Ohm is placed in a vessel containing 0.5 kg of water at 20 ° C, and connected to a network with a voltage of 220 V. After 20 minutes, the boiler was turned off. How much water has boiled away if the efficiency of the spiral is 80%?

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

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 the magnet or removed from the magnet

According to the law of electromagnetic induction, an inductive current appears in the circuit when the magnetic flux through the circuit changes. It does not matter what the reason for the change is, it can be the movement of the magnet relative to the circuit, or the movement of the circuit relative to the magnet. It also does not matter how the flow changes, whether it increases or decreases, only the direction of the induction current is determined by this. Since the magnet is stationary under the conditions of the problem, 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 pushed into a short-circuited coil: once quickly, another time slowly. Compare the values ​​of the inductive current in these cases.

A.I 1 \u003d I 2 \u003d 0 B. I 1 \u003d I 2 \u003d 0 C. I 1\u003e 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, and a fixed magnet is located in the third ring. In which ring does the induced current flow?

3. A light wire ring is suspended from a thread. When sliding into the magnet ring south pole it will: 1) repel the magnet; 2) be attracted to a magnet; 3) motionless; 4) first repel, then attract.

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) 4 V;

3) 6 V; 4) 8 V.

5. The magnetic flux F, penetrating the conductive circuit of the wire frame, changes over time as shown in graph 1. In which case is the current in the frame 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 in 4 s, an induction EMF of 0.8 V occurs in the coil. What is the inductance of the coil?

1) 0.1 H. 2) 0.4 H. 3) 1.6 Gn. 4) 6.4 Gn.

7. In fig. 2 shows the electrical circuit. 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 significance of the current strength in a coil with an inductance of 2 H, if the energy of the magnetic field of the coil is 16 J?

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

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

10. A straight conductor with a length of 1.4 m and a resistance of 2 ohms, located in a uniform magnetic field with an induction of 0.25 T, is subject to a force of 2.1 N. 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 the general view was first solved by: 1) Oersted; 2) Lenz; 3) Ampere; 4) Faraday.

12. 100 square wire frame 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 lines of magnetic induction, then at the time t \u003d 3s, the induction emf acts on the frame, equal to:

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

13. The main property of the induction electric field is: 1) the field is created by a changing magnetic field; 2) the field is created 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 field induction increases uniformly from 1 to 5 T in 0.1 s. Determine the induction emf that occurs in the coil if the area of ​​​​the turns is 6 cm.

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

17. What is the current strength in a coil with an inductance of 40 mH, if the magnetic field energy is 0.18 J?

18. Suppose that a magnet is pushed into a superconductor ring. How will the magnetic flux passing through the ring change in this case?

19. Explain the transformation of energy that occurs when the magnetic needle turns near the wire through which the current is passed.

(Give a detailed answer)


Physics problem - 4083

2017-09-30
A magnet is inserted into a short-circuited coil: once quickly and once slowly. Is the same charge passing through the circuit in both cases? Is the same amount of heat released?


Solution:

Let the resistance of the coil be $R$. If in a short time $\Delta t$ the magnetic flux through the circuit changes by $\Delta \Phi$, then induction EMF appears in the coil $\mathcal(E)_(i) = - \frac( \Delta \Phi )( \Delta t)$. Induction current $I = \frac( \mathcal(E)_(i))(R) = - \frac(1)(R) \cdot \frac( \Delta \Phi)( \Delta t)$. During the time $\Delta t$, the charge $\Delta q = I \Delta t = - \frac( \Delta \Phi)( R)$ passes through the circuit. Total charge $q = \sum \Delta q = - \frac(1)(R) \sum \Delta \Phi = - \frac( \Phi)(R)$. Here $\Phi$ is the final value of the magnetic flux (the initial value is zero). Hence $q$ does not depend on the speed of the process. The amount of heat released in the circuit $Q$ is equal to the work of external forces: $Q ​​= q \mathcal(E)_(i)$. Since the charge $q$ is the same in both cases, and $\mathcal(E)_(i)$ is larger when the magnet moves quickly, the amount of heat in the first case is greater. This conclusion can be reached in another way: $Q = A = Fs$, where $A$ is the mechanical work done when the magnet is introduced. The displacement of the magnet $s$ is the same in both cases, and $F$ is greater in the first case ($F$ is the repulsion force of the magnet from the coil due to the appearance of inductive currents).
Answer: the charge is the same; the amount of heat is greater when the magnet moves quickly.

Are you familiar with electromagnetic induction? // Quantum. - 1989. - No. 6. - S. 40-41.

By special agreement with the editorial board and the editors of the journal "Kvant"

Hope to get electricity through
ordinary magnetism at different times
encouraged me to experiment
inductive action of electric currents.
M. Faraday

Faraday devoted his entire life to proving that not a single electrical or magnetic process occurring in nature proceeds in isolation. Faraday's deep faith in the interconnectedness of all the forces of nature led him, after many years of failure, to a unique discovery.

A new effect, as often happens, was then discovered in a multitude of outwardly 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. It was Faraday's discovery that made it possible to convert mechanical energy into electrical energy, transfer energy over a distance, and thus laid the foundation for modern technical civilization.

The work of Faraday and his outstanding contemporaries made it possible, step by step, to create a unified picture of electromagnetism.

In studying this section of physics, you will not only explain the facts and observations you know, but you will also be able to understand electromagnetic phenomena on both cosmic and microscopic scales.

Questions and tasks

  1. How to move a magnet to turn an arrow north pole to the observer?

  2. The horizontal circular frame is in a magnetic field directed vertically upwards. What will be the direction of the induced current when the loop is viewed from above if the field decreases with time?
  3. At what positions of a frame rotating at a constant speed near a rectilinear current-carrying conductor, the EMF arising in it will be the greatest? least?

  4. A magnet is pushed into the short-circuited coil first quickly and then slowly. Is the same charge carried by the inductive current? Is the same amount of heat released in the coil?
  5. How will a magnet fall in a long copper tube? Ignore air resistance.
  6. The ends of the wire folded in half are connected to a galvanometer. Why does the instrument pointer stay at zero when the wire crosses the magnetic field lines?
  7. A metal coin lies on a vertically located coil. Why does it heat up when an alternating current flows through the coil, and remains cold when it is constant?
  8. A high frequency current flows through a straight conductor. How will the resistance of this conductor change if it is shaped like a solenoid?
  9. Conductor AB moves in such a way that a current flows through it from a point BUT to the point AT. Which of these points has the highest potential?

  10. Two identical planes fly horizontally at the same speed, one near the equator, the other near the pole. Which of them has a large potential difference at the ends of the wings?

  11. The rotor of a running electric generator experiences braking. What is the nature of the forces causing this inhibition?
  12. Two circular conductors are located perpendicular to each other. Will there be an induction current in the conductor BUT with changes in current in the circuit AT?

  13. A superconductor ring is located near a permanent magnet and is pierced by a magnetic flux Ф. There is no current in the ring. What will be the magnetic flux through this ring if the magnet is removed?

    14. Microexperience

    Suspend a horseshoe magnet on a string above an aluminum foil disc capable of rotating about an axis passing through its center. If you unwind the magnet, the disk will begin to rotate. Which way. Why?

    It is curious that…

    AT latest types electrical machines do not have any mechanical moving parts. In the so-called MHD (magnetohydrodynamic) - a generator instead of a wire conductor between the poles of the magnet moves the plasma 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 appears in the external circuit.

    Faraday carried for years in his vest pocket a small bar magnet and a wire coil as a constant reminder of the unsolved problem of magnetic field generation of electric current.

    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 calming" in measuring instruments and circular saws and ... the well-known electric energy meter.

    Having independently come up with the idea of ​​electromagnetic rotation, Faraday, using a mercury contact, carried out a continuous rotation of a magnet around a current-carrying conductor. 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 the school laboratory by placing a superconducting ceramic tablet over a magnet: it will “float” above it.

    What to read in "Quantum" about electromagnetic induction

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

    Answers

    1. Push into coil.
    2. Counterclock-wise.
    3. The induction emf will have smallest value when the frame is in a plane passing through the wire, the largest - when the frame is perpendicular to this plane.
    4. No, since the flux of the magnetic induction of the circuit AT does not penetrate the contour BUT.
    5. Same. No, because the amount of heat is proportional to the speed of the magnet.
    6. 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.
    7. Along with the usual friction, the rotor is also slowed down by the ampere forces acting on it from the stator magnetic field.
    8. An airplane flying near the Pole.
    9. In the two halves of the wire, equal in magnitude, but opposite in sign, induction emfs arise, which are mutually compensated.
    10. At the point AT, since on the site BCA, where there are no sources of EMF, the current comes from AT to BUT.
    11. With alternating current, eddy currents occur in the coin, with direct current, no.
    12. will increase.
    13. 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. Therefore, 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 in such a way that the magnetic field created by them slows down the movement of the magnet. According to Newton's third law, an equal and opposite force acts on the disk and drags it along with the magnet.

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