Questions.
1. How can we experimentally detect the presence of a force acting on a current-carrying conductor in a magnetic field?
It is necessary to place a conductor with current between the poles of the magnet so that the direction of the current is perpendicular to the lines magnetic field, and the fastening allowed the conductor to move. When current passes, the conductor will deflect, but this will not happen if the magnet is removed.
2. How is a magnetic field detected?
A magnetic field can be detected by its effect on a magnetic needle or on a current-carrying conductor.
3. What determines the direction of the force acting on a current-carrying conductor in a magnetic field?
From the direction of the current and the direction of the magnetic lines.
4. How is the left-hand rule read for a current-carrying conductor in a magnetic field? for a charged particle moving in this field?
If you place left hand so that the lines of magnetic induction enter the palm perpendicular to it, and the extended four fingers indicate the direction of the current (the direction of movement of the positively charged particle), then set back at 90° thumb will show the direction of the force acting on the conductor.
5. What is taken as the direction of the current in the outer part electrical circuit?
This direction is from the positive pole to the negative pole.
6. What can you determine using the left-hand rule?
The direction of the force acting on the conductor, knowing the direction of the current and magnetic field lines. Direction of current by knowing the direction of force and magnetic lines. The direction of magnetic field lines, knowing the direction of the current and the force acting on the conductor.
7. In what case is the force of a magnetic field on a current-carrying conductor or a moving charged particle equal to zero?
In the case when the direction of current movement or the direction of particle speed coincides with the direction of the magnetic induction lines, the force of the magnetic field is zero.
Exercises.
1. In which direction will the light aluminum tube roll when the circuit is closed (Fig. 112)?
Using the left hand rule we determine what is to the right.
2. Figure 113 shows two bare conductors connected to a current source and a light aluminum tube AB. The entire installation is located in a magnetic field. Determine the direction of the current in the tube AB if, as a result of the interaction of this current with the magnetic field, the tube rolls along the conductors in the direction indicated in the figure. Which pole of the current source is positive and which is negative?
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According to the left-hand rule, current moves from point A to B, therefore the upper pole of the current source is positive, and the lower pole is negative.
3. Between the poles of the magnets (Fig. 114) there are four current-carrying conductors. Determine which direction each of them is moving.
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Left - up, down. Right - down, up.
4. Figure 115 shows a negatively charged particle. moving with speed v in a magnetic field. Make the same drawing in your notebook and indicate with an arrow the direction of the force with which the field acts on the particle.
5. A magnetic field acts with a force F on a particle moving with speed v (Fig. 116). Determine the sign of the particle's charge.
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The sign of the particle charge is negative (we apply the left-hand rule).
Test Check 1. A magnetic field is generated by an electric current. 2. A magnetic field is created by moving charged particles. 3. The direction of the magnetic line at any point is conventionally taken to be the direction that indicates North Pole magnetic needle placed at this point. 4. Magnetic lines leave the north pole of the magnet and enter the south pole.
LEFT HAND RULE for a charged particle 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 particle), then the thumb placed at 90 degrees will show the direction of the force acting on the particle.
Is it possible to defend against an action? magnetic forces? Oddly enough, the substance impermeable to magnetic forces is the same iron that is so easily magnetized! Inside the iron ring, the compass needle is not deflected by a magnet placed outside the ring. It is magnetized
Thanks to today's video tutorial, we will learn how to detect a magnetic field by its effect on electricity. Let's remember the rule of the left hand. Through experiment we 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? a large number of 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 in such a way that magnetic lines entered the palm, four extended fingers indicated the direction of the electric current - then the bent thumb would 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.
Recall that electric current is a directed movement 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.
“Detection of a magnetic field by its effect on an electric current. Left hand rule»
Lesson objectives:
Educational:
Study how a magnetic field is detected by its effect on an electric current, study the left-hand rule, repeat the previously covered definitions of the electric field, magnetic field, the 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:
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 Creative skills, 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 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 permanent magnet, near a current-carrying conductor.)
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 places where juveniles 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 arises 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 current-carrying conductor 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 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 90° the thumb will indicate 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 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 a positively charged particle (or against the movement of a negatively charged ), then the thumb placed 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, by shielding 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 a 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 an electrical 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 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.
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 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. The first such 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 the same 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 a large number of similar experiments were carried out, 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 in such a way 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 in this case we can also use the left-hand rule 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 physics textbook. Ed. G.S. Landsberg. T. 2. - M., 1974. Yavorsky B.M., Pinsky A.A. Fundamentals of Physics. T.2. - M.: Fizmatlit, 2003.
