“Detection of a magnetic field by its effect on electric current. Left hand rule»
Lesson objectives:
Educational:
Study how a magnetic field is detected by its effect on electric current, study the left-hand rule, repeat previously covered definitions electric field, magnetic fields, conditions for their occurrence, properties; consolidate the rules of the right and left hands with the help of exercises;
consolidate knowledge on previous topics;
teach to apply the knowledge acquired in the lesson;
show connection with life;
expand interdisciplinary connections.
Educational:
to develop interest in the subject, in learning, creative attitude, cultivate a conscientious attitude towards learning, instill skills like independent work, and working in a team, to cultivate interest in the subject.
Educational:
develop the physical thinking of students, their creativity, ability to independently formulate conclusions,
develop speech skills;
develop the ability to highlight the main thing, draw conclusions, and perform the necessary tasks; develop logical thinking and attention, ability to analyze, draw conclusions.
I.1 Verification homework, knowledge and skills
Test work. We write down the answers on a card.
1. The magnetic field is generated by ___________ electric shock.
2. The magnetic field is created by ______________ Dseeing each other charged particles.
3. The direction of a magnetic line at any point is conventionally taken to be the direction that indicates _________ northern the pole of a magnetic needle placed at this point.
4. Magnetic lines come out of _________ Withnorthern poles of the magnet and enter into southern ________.
We exchanged papers and checked each other
1.Indicate the direction of currents in conductors using the gimlet rule
2. Indicate the direction of the magnetic field lines around the current-carrying conductor using the gimlet rule
3.A current is passed through a coil containing a steel rod. specified direction. Determine the poles of the resulting electromagnet, the poles of the magnetic needle. 
4.How do 2 coils with current interact with each other?
2. Introduction to learning new material.
What is a magnetic field?
This « special condition space."
Near what bodies can a magnetic field be detected?(near a permanent magnet, near a conductor with current.)
How can you detect the magnetic field of, for example, the Earth?
(using a magnetic needle).
How can a magnetic field be detected? It does not affect our senses - it has no smell, color, or taste. We cannot, however, say with certainty that in the animal world there are no creatures that sense a magnetic field. In the USA and Canada, to drive octopuses away from the places where fry accumulate on rivers flowing into the Great Lakes, electromagnetic barriers. Scientists explain the ability of fish to navigate the ocean by their reaction to magnetic fields...
Today in class we will learn how to detect a magnetic field by its effect on an electric current and learn the left hand rule.
Explanation of new material
For any current-carrying conductor placed in a magnetic field and not coinciding with its magnetic lines, this field acts with some force; the presence of such a force can be seen using the following experiment: the conductor is suspended on flexible wires, which are connected to the batteries through a key. The conductor is placed between the poles of a horseshoe magnet, i.e. it is in a magnetic field. When the key is closed, an electric current appears in the circuit, and the conductor begins to move. If you remove the magnet, then when the circuit is closed, the current-carrying conductor will not move. (Demo1) 
Conclusion: 1. This means that a certain force acts on the current-carrying conductor from the magnetic field, deflecting it from its original position.
Let's find out what determines the direction of the force acting on a conductor carrying current in a magnetic field.
(Demonstration 2) Conclusion: 2. Experience shows that when the direction of the current changes, the direction of movement of the conductor also changes, and therefore the direction of the force acting on it.
(Demonstration3) let's change the direction of the magnetic field lines.
Conclusion: 3. The direction of the force will also change if, without changing the direction of the current, the poles of the magnet are swapped
Consequently, the direction of the current in the conductor, the direction of the magnetic field lines and the direction of the force acting on the conductor are interconnected.
The direction of the force acting on a current-carrying conductor in a magnetic field can be determined using the left-hand rule. In the simplest case, when the conductor is located in a plane perpendicular to the magnetic field lines, this rule is as follows: if left hand positioned so that the magnetic field lines enter the palm perpendicular to it, and the four fingers are directed along the current, then set at 90° thumb will show the direction of the force acting on the conductor.
The direction of current in the external part of the electrical circuit (i.e. outside the current source) is taken to be the direction from the positive pole of the current source to the negative.
Using the left-hand rule, you can determine not only the direction of the force acting in a magnetic field on a current-carrying conductor. Using this rule, we can determine the direction of the current (if we know the directions of the magnetic field lines and the force acting on the conductor), the direction of the magnetic lines (if the directions of the current and force are known), and the sign.
The force of a magnetic field on a current-carrying conductor is zero if the direction of the current in the conductor coincides with the magnetic field lines or is parallel to them.
When using the left-hand rule, this should be remembered.
In other words, the four fingers of the left hand should be directed against the flow of electrons in the electrical circuit. In conducting media such as electrolyte solutions, where an electric current is created by the movement of charges of both signs, the direction of the current, and therefore the direction of the four fingers of the left hand, coincides with the direction of movement of positively charged particles.
Using the left-hand rule, you can determine the direction of the force with which the magnetic field acts on a single particle moving in it, both positively and negatively charged. For the most simple case when the particle moves in a plane perpendicular to magnetic lines, this rule is formulated as follows: if the left hand is positioned so that the magnetic field lines enter the palm perpendicular to it, and four fingers are directed along the movement of a positively charged particle (or against the movement of a negatively charged one), then the thumb set at 90° will show the direction of the force acting on the particle.
Using the left-hand rule, you can determine not only the direction of the force acting in a magnetic field on a current-carrying conductor or a moving charged particle. Using this rule, we can determine the direction of the current (if we know the directions of the magnetic field lines and the force acting on the conductor), the direction of the magnetic lines (if the directions of the current and force are known), the sign of the charge of the moving particle (by the direction of the magnetic lines, force and speed of movement particles).
The force of a magnetic field on a current-carrying conductor or a moving charged particle is zero if the direction of the current in the conductor or the speed of the particle coincides with or parallel to the magnetic field lines. Using the left-hand rule, you can determine the direction of the force with which the magnetic field acts on a single particle moving in it, both positively and negatively charged (see Fig. 3a, b, c). 
APPLICATION:
Did you know, What…
A strong magnetic field affects the growth of crystals: for example, copper single crystals formed in strong magnetic fields have a more perfect crystal lattice.
A strong magnetic field is also used to treat such a common and dangerous disease as heart rhythm disturbances (arrhythmia). The heart is an organ that continuously performs rhythmic contractions, the period of which is determined by weak electrical signals sent by the brain. With heart disease, the rhythm of contractions is disrupted. In especially severe cases, defibrillators are used - devices that generate impulses high voltage, and the electrodes are applied directly to the heart area, which often results in a burn. When using a pulsating magnetic field that causes induced currents V nerve cells, this danger is eliminated.
Magnetic counter guard
In order to somehow protect against theft, store owners attach special tags to the goods that come off at checkpoint after the money has been paid. Tags - tiny antennas - if you try to take a purchase out of a store without paying, they trigger an alarm at the exit due to the resonant amplification of the radio signal coming from small radio transmitters installed at the exit. However, this method turned out to be not entirely reliable: a thief can shield the tag with a piece of foil or own body, deceive the signaling device.
To prevent this from happening, Checkmate Systems has developed new system. The control tag is now made from magnetic material, and at the exit of the store there are highly sensitive magnetometers.
The system is adjusted so that it does not respond to small metal objects: keys, watches, buckles and jewelry, but desperately rings when it notices the control tag
TREATMENT WITH MAGNETS
The phenomenon of magnetism has been known to people for a very long time.
The ancients attributed many wonderful properties to magnets. It was believed that a “magnetic stone” crushed into powder would cure dropsy and insanity, stop any bleeding, resolve cancerous tumors, and even give immortality. Although some healers believed that magnet was a strong poison, others suggested using it as an antidote.
Queen Cleopatra of Egypt wore a magnetic amulet to preserve youth and beauty. About the use of permanent magnets
for medicinal purposes there are references in the works of Hippocrates, Paracelsus, scientists ancient China.
In the 17th century, a method of applying to a “painful place” magnetic iron ore became widespread and was even mentioned in medical books.
Magnetic therapy was also used famous doctor 18th century Franz Antoine Mesmer for the treatment of pain, gout, nervous disorders and colic. The great Mozart was so impressed by Mesmer's healing success that he included a description of the healing effects of magnets in his opera "Cosi fan tutti." Mesmer treated patients with magnets, which he moved over the patient's body. He made special vessels that he filled chemicals to produce electric charge. These vessels had metal handles. People stood next to them and held hands to gain magnetic power.
Use in technology:
Electric motors;
Electrical measuring instruments;
Loudspeakers, speakers.
Fixing the material. Problem solving 
Results
Today in class we learned how to detect a magnetic field by its effect on an electric current. Considered the left hand rule for determining the direction of force
V.Homework:§ 46, ex. 36 (2, 3, 4, 5)………make up your tasks
Rice. 3. Left hand rule for charged particles.
To top it off, it should be noted that the force of a magnetic field on a current-carrying conductor or a moving charged particle is zero if the direction of the current in the conductor or the speed of movement of the particle coincides with the magnetic induction line or is parallel to it.
Due to the current strength, an Ampere force arises, which rotates the frame, but due to this, an elastic force of the spring arises, balancing the Ampere force. Due to this, the rotation of the arrow is proportional to the current strength.
From the 8th grade physics course, you know that for any current-carrying conductor placed in a magnetic field and not coinciding with its magnetic lines, this field acts with some force.
The presence of such a force can be shown using the installation shown in the figure. The three-sided frame ABCD, made of copper wire, is suspended on hooks so that it can freely deviate from the vertical. The BC side is located in the region of the strongest magnetic field of the arc-shaped magnet, located between its poles (Fig. a). The frame is connected to the current source in series with a rheostat and a key.
Rice. The effect of a magnetic field on a current-carrying conductor
When the key is closed, an electric current arises in the circuit, and the BC side is drawn into the space between the poles (Fig. b).
If you remove the magnet, then when the circuit is closed, the conductor BC will not move. This means that from the side of the magnetic field, a certain force acts on the current-carrying conductor, deflecting it from its original position.
The effect of a magnetic field on a current-carrying conductor can be used to detect the magnetic field in a given region of space.
Of course, it is easier to detect the magnetic field using a compass. But the effect of a magnetic field on the magnetic compass needle located in it, in essence, also comes down to the effect of the field on elementary electric currents circulating in molecules and atoms magnetic substance, from which the arrow is made.
Thus, a magnetic field is created by an electric current and is detected by its effect on the electric current.
Let's change the direction of the current in the circuit by swapping the wires in the sockets of the insulating rod (Fig.). In this case, the direction of movement of the conductor BC will also change, and therefore the direction of the force acting on it.
Rice. The direction of the force acting on a current-carrying conductor in a magnetic field depends on the direction of the current
The direction of the force will also change if, without changing the direction of the current, the poles of the magnet are swapped (that is, the direction of the magnetic field lines is changed). Consequently, the direction of the current in the conductor, the direction of the magnetic field lines and the direction of the force acting on the conductor are interconnected.
The direction of the force acting on a current-carrying conductor in a magnetic field can be determined using the left-hand rule.
In the simplest case, when the conductor is located in a plane perpendicular to the magnetic field lines, this rule is as follows: if the left hand is positioned so that the magnetic field lines enter the palm perpendicular to it, and four fingers are directed along the current, then the left hand The 90° thumb will show the direction of the force acting on the conductor (Fig.).
Rice. Applying the left-hand rule to a current-carrying conductor
Using the left-hand rule, it should be remembered that the direction of current in an electrical circuit is taken to be the direction from the positive pole of the current source to the negative. In other words, the four fingers of the left hand should be directed against the flow of electrons in the electrical circuit. In conducting media such as electrolyte solutions, where electric current is created by the movement of charges of both signs, the direction of the current, and therefore the direction four fingers left hand coincides with the direction of movement of positively charged particles.
Using the left-hand rule, you can determine the direction of the force with which the magnetic field acts on individual particles moving in it, both positively and negatively charged.
For the simplest case, when a particle moves in a plane perpendicular to the magnetic lines, this rule is formulated as follows: if the left hand is positioned so that the magnetic field lines enter the palm perpendicular to it, and four fingers are directed along the movement of the positively charged particle (or against the movement of a negatively charged one), then the thumb placed at 90° will show the direction of the force acting on the particle (Fig.).
Rice. Application of the left-hand rule to charged particles moving in a magnetic field
Using the left-hand rule, you can also determine the direction of the current (if we know the direction of the magnetic field lines and the force acting on the conductor), the direction of the magnetic lines (if the directions of the current and force are known), the sign of the charge of the moving particle (in the direction of the magnetic lines, force and speed particle movement), etc.
It should be noted that the force of a magnetic field on a current-carrying conductor or a moving charged particle is zero if the direction of the current in the conductor or the speed of the particle coincides with the magnetic induction line or is parallel to it (Fig.).
Rice. The magnetic field does not act in cases where a straight conductor with current or the speed of a moving charged particle is pasparallel to or coincident with magnetic field lines
Homework.
Task 1. Answer the questions.
- What experiment allows us to detect the presence of a force acting on a current-carrying conductor in a magnetic field?
- How is a magnetic field detected?
- What determines the direction of the force acting on a current-carrying conductor in a magnetic field?
- Formulate the left-hand rule for a current-carrying conductor in a magnetic field; for a charged particle moving in this field.
- What can you determine using the left-hand rule?
- In what case is the force of a magnetic field on a current-carrying conductor or a moving charged particle equal to zero?
Task 2. Solve the puzzle.
The file “This is interesting!” is attached to the lesson. You can download the file at any time convenient for you.
Sources used:
http://www.tepka.ru/fizika_9/36.html
Detection of a magnetic field by its effect on electric current. Left hand rule
Electromagnetic phenomena
Thanks to today's video tutorial, we will learn how a magnetic field is detected by its effect on an electric current. Let's remember the rule of the left hand. Through experiment we will learn how a magnetic field is detected by its effect on another electric current. Let's study what the left hand rule is.
In this lesson, we will discuss the issue of detecting a magnetic field by its effect on an electric current, and get acquainted with the left-hand rule.
Let's turn to experience. First similar experiment to study the interaction of currents was carried out by the French scientist Ampere in 1820. The experiment was as follows: an electric current was passed through parallel conductors in one direction, then the interaction of these conductors was observed in different directions.
Rice. 1. Ampere's experiment. Co-directional conductors carrying current attract, opposite conductors repel
If you take two parallel conductors, through which electric current passes in one direction, then in this case the conductors will attract each other. When electric current flows in different directions in the same conductors, the conductors repel each other. Thus, we observe the force effect of a magnetic field on an electric current. So, we can say the following: a magnetic field is created by an electric current and is detected by its effect on another electric current (Ampere's force).
When was it carried out? large number similar experiments, a rule was obtained that connects the direction of magnetic lines, the direction of electric current and the force action of the magnetic field. This rule is called left hand rule. Definition: the left hand must be positioned so that the magnetic lines enter the palm, four extended fingers indicate the direction of the electric current - then the bent thumb will indicate the direction of the magnetic field.
Rice. 2. Left hand rule
Please note: we cannot say that where the magnetic line is directed, the magnetic field acts there. Here the relationship between quantities is somewhat more complicated, so we use left hand rule.
Let us remember that electric current is the directional movement of electric charges. This means that a magnetic field acts on a moving charge. And we can take advantage of in this case also the rule of the left hand to determine the direction of this action.
Take a look at the picture below for different uses of the left-hand rule, and analyze each case yourself.
Rice. 3. Various applications of the left-hand rule
Finally, one more important fact. If the electric current or the speed of a charged particle is directed along the magnetic field lines, then there will be no effect of the magnetic field on these objects.
List of additional literature:
Aslamazov L.G. Movement of charged particles in electric and magnetic fields // Quantum. - 1984. - No. 4. - P. 24-25. Myakishev G.Ya. How does an electric motor work? // Quantum. - 1987. - No. 5. - P. 39-41. Elementary textbook physics. Ed. G.S. Landsberg. T. 2. - M., 1974. Yavorsky B.M., Pinsky A.A. Fundamentals of Physics. T.2. - M.: Fizmatlit, 2003.
Option 1
A. electrons
IN. negative ions
2. The operation of an electric motor is based on...
A. the effect of a magnetic field on a conductor carrying electric current
B. electrostatic interaction of charges
B. the action of an electric field on an electric charge
G. phenomenon of self-induction
3. A positively charged particle with a horizontally directed velocity v. flies into the field region perpendicular to the magnetic lines (see figure). Where is the force acting on the particle directed?
B. Vertically up
B. Vertically down
4. Electric circuit, consisting of four straight horizontal conductors (1-2, 2-3, 3-4, 4-1) and a source DC, is in a uniform magnetic field, power lines which are directed vertically upward (see figure, top view). The force acting on conductor 4-1 is directed 
A. horizontally to the left
B. horizontally to the right
B. vertically down
G. vertically up
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Test topic: "Detection of a magnetic field by its effect on electric current. Left hand rule"
Option 2
1. The direction of the current, according to its representation in magnetism, coincides with the direction of movement
A. negative ions
B. electrons
B. positive particles
2. The magnetic field acts with a non-zero force on...
A. an ion moving perpendicular to the lines of magnetic induction
B. ion moving along magnetic induction lines
B. atom at rest
G. resting ion
3. Select the correct statement(s).
A: to determine the direction of the force acting on a positively charged particle, four fingers of the left hand should be placed in the direction of the particle’s speed
B: to determine the direction of the force acting on a negatively charged particle, four fingers of the left hand should be placed opposite the direction of the particle’s speed
A. Only B
B. neither A nor B
B. and A and B
G. Only A
4. A negatively charged particle with a horizontally directed velocity v flies into the field region perpendicular to the magnetic lines (see figure). Where is the force acting on the particle directed?
A. horizontally to the right in the plane of the drawing
B. horizontally to the left in the plane of the drawing
=============================
Test topic: "Detection of a magnetic field by its effect on electric current. Left hand rule"
Option 3
1. The direction of the current, according to its representation in magnetism, coincides with the direction of movement
A. negative ions
B. electrons
B. positive particles
2. The square frame is located in a uniform magnetic field as shown in the figure. The direction of the current in the frame is indicated by arrows. The force acting on the bottom side of the frame is 
A. directed downwards
B. from the plane of the sheet to us
V. in the plane of the sheet from us
G. directed upwards
3. An electric circuit consisting of four straight horizontal conductors (1-2, 2-3, 3-4, 4-1) and a direct current source is in a uniform magnetic field, the lines of force of which are directed vertically upward (see Fig. , top view).The force acting on conductor 4-1 is directed
A. horizontally to the right
B. vertically up
B. horizontally to the left
D. vertically down
A. on us from the drawing
B. horizontally to the left
V. from us to the drawing
D. horizontally to the right
=============================
Test topic: "Detection of a magnetic field by its effect on electric current. Left hand rule"
Option 4
1. The direction of the current, according to its representation in magnetism, coincides with the direction of movement
A. electrons
B. positive particles
B. negative ions
2. An electric circuit consisting of four straight horizontal conductors (1-2, 2-3, 3-4, 4-1) and a direct current source is located in a uniform magnetic field, the lines of force of which are directed vertically upward (see Fig. , top view).The force acting on conductor 4-1 is directed
A. horizontally to the left
B. vertically down
B. vertically up
D. horizontally to the right
3. The square frame is located in a uniform magnetic field as shown in the figure. The direction of the current in the frame is indicated by arrows. The force acting on the bottom side of the frame is
A. directed upwards
B. from the plane of the sheet to us
V. in the plane of the sheet from us
G. directed downwards
4. An electric circuit consisting of four straight horizontal conductors (1-2, 2-3, 3-4, 4-1) and a direct current source is in a uniform magnetic field, the lines of which are directed horizontally to the right (see Fig., top view). The force acting on conductor 1-2 is directed
A. horizontally to the right
B. from us to the drawing
B. horizontally to the left
G. on us from the drawing
=============================
Test topic: "Detection of a magnetic field by its effect on electric current. Left hand rule"
Option 5
1. A square frame is located in a uniform magnetic field as shown in the figure. The direction of the current in the frame is indicated by arrows. The force acting on the bottom side of the frame is
A. from the plane of the sheet to us
B. directed upwards
V. directed downwards
G. in the plane of the sheet from us
2. An electric circuit consisting of four straight horizontal conductors (1-2, 2-3, 3-4, 4-1) and a direct current source is in a uniform magnetic field, the lines of which are directed horizontally to the right (see Fig., top view). The force acting on conductor 1-2 is directed
A. horizontally to the left
B. from us to the drawing
B. horizontally to the right
G. on us from the drawing
3. The main purpose of the electric motor is to convert...
A. electrical energy into mechanical energy
B. mechanical energy V electrical energy
IN. internal energy into mechanical energy
G. mechanical energy in various types energy
4. The direction of the current, according to its representation in magnetism, coincides with the direction of movement
A. positive particles
B. electrons
In negative ions
=============================
=============================
Test topic: "Detection of a magnetic field by its effect on electric current. Left hand rule"
Correct answers:
Option 1
Question 1 - B;
Question 2 - A;
Question 3 - G;
Question 4 - A;
Option 2
Question 1 - B;
Question 2 - A;
Question 3 - B;
Question 4 - G;
Option 3
Question 1 - B;
Question 2 - B;
Question 3 - B;
Question 4 - A;
Option 4
Question 1 - B;
Question 2 - A;
Question 3 - B;
Question 4 - G;
Option 5
Question 1 - G;
Question 2 - G;
Question 3 - A;
Question 4 - A;
Let's remember how we can detect a magnetic field, because it is invisible and our senses do not perceive it? A magnetic field can only be detected by its effect on other bodies, for example, on a magnetic needle. The field acts on the arrow with some force, causing it to change its original orientation. A magnetic field is created when charges move along a conductor in a circuit or due to the same orientation of ring currents in permanent magnets. Oersted's discovery of the relationship between electricity and magnetism prompted scientists to conduct various experiences, with the help of which new patterns were established. We already know that a magnetic field is created around a current-carrying conductor. How will a current-carrying conductor behave if it is placed in a different magnetic field?
Let's conduct an experiment.
Let's assemble an installation consisting of a movable copper frame mounted on an insulating rod, a current source, a rheostat and a key. Turn on the circuit. The frame will remain motionless. We already know that there is a magnetic field around the conductor, but we cannot detect it. Let's open the circuit. Let's place an arc-shaped magnet near the frame so that the horizontal part of the frame is located between its poles (since the magnetic field is strongest near the poles). There is also a magnetic field around the arc magnet, but as long as there is no current flowing in the frame, we also cannot detect it. Let's close the circuit. The frame began to move and deviated to the left. A certain force directed towards the magnet set the frame in motion and deflected it at a certain angle. The magnetic field around a conductor is created by an electric current. A magnetic field can be detected by its effect on electric current. The figure shows the direction of current movement in the conductor. The current direction is chosen to be the movement from the positive pole of the current source to the negative pole. Let's change the direction of the current by changing the polarity. We close the circuit and again detect the magnetic field by the action on the frame - it has deviated by a certain angle in the direction opposite to the magnet. If in the last experiment the arrangement of the magnet poles is reversed, the frame will be drawn into the arc magnet. The direction of the force under which a conductor moves in a particular direction can be determined by the left-hand rule. This is a mnemonic rule, with the help of which it is easy to determine where the force will be directed, let's denote it in the figure with the letter F. If the left hand is positioned so that the lines of the magnetic field enter perpendicularly into the palm, four fingers show the direction of the current, then the thumb set at 900 will show the direction of the force acting on the conductor. Remember that the direction of current is the movement from plus to minus. So they move in a conducting medium positive charges, creating a current. So, according to the rule right hand You can also determine the direction of the force for a positively charged particle. And when we want to determine the direction of the force acting on negative particle, four fingers should be positioned opposite the movement of the negatively charged particle.
Determine how the poles of the magnet are located, the direction of the current and the force acting from the magnetic field on the current-carrying conductor. Let's use the left-hand rule. The four fingers of the left hand show the direction of the current. The conductor is located perpendicular to the plane, and since we see the feathering of the arrow (cross), therefore, the current moves away from us. The direction of the force acting from the magnetic field is shown by the thumb positioned 900 degrees away. The palm of the left hand looks up, therefore, the magnetic field lines will enter it, that is North Pole The magnet should be located on top. If the direction of the current in the conductor or the speed of the particle coincides with the magnetic induction line or is parallel to it, then the force of the magnetic field or the moving charged particle is zero.
