Magnetic lines of the magnetic field of the current represents. Magnetic field lines
An electric motor is a motor that converts electrical energy into mechanical energy.
The main part of the electric motor is a circuit (frame, coil) with current located in a strong magnetic field (Fig. 1). A torque acts on the circuit in a magnetic field, as a result of which the circuit rotates and stops in the equilibrium position, i.e. in a position in which its magnetic moment is directed parallel to the magnetic induction \(~\vec p_m\upuparrows \vec B\) (the contour plane is perpendicular to the magnetic field induction lines). If, when the circuit passes through the equilibrium position, the direction of the current changes to the opposite, then the direction of the magnetic moment will also change. Having passed the equilibrium position by inertia, the circuit will make another half turn. If you periodically change the direction of the current, the circuit will begin to rotate. Changing the direction of the current is carried out automatically using a device called a collector. The collector consists of two metal half-cylinders, to which the ends of the circuit are connected. Through them and sliding contacts (brushes), the circuit is connected to the current source.
The greatest moment acts on a circuit whose plane is parallel to the magnetic induction \(\vec B\). Consequently, if you place two circuits perpendicular to each other and bring their ends to a quarter-ring manifold (Fig. 2), then the torque will increase sharply and the smoothness of the moving part of the engine (rotor) will increase.
In industrial motors, the magnetic field is created by the winding of an electromagnet; grooves are made in the rotor into which many turns of one section are placed (instead of a frame); the various sections are laid at an angle to each other, and their ends are brought out on opposite sides of the commutator, to which the brushes connected to the current source are pressed. From the current source, voltage is supplied to the electromagnets of the stator (the stationary part of the engine). Current flows through each section only when its plates touch the brushes, i.e. when the plane of this section is parallel to the magnetic induction vector. In this case, the sections alternately create the largest torque.
A magnet or electromagnet that creates a magnetic field is often called an inductor, and the frame (winding) through which electric current is passed is called an armature.
The main operating characteristic of an electric motor is torque M, created on the motor shaft by the Ampere force acting on the armature windings:
\(~2FrN = 2IBlrN ,\)
Where I- current strength in the winding, IN- magnetic field induction, l- length of the conductor, r- rotor radius, N- number of turns in the winding.
Such DC motors are used in transport (in electric locomotives, trams, trolleybuses), on cranes, and in many household electrical devices (electric shavers, tape recorders, etc.).
With the help of a DC electric motor - the starter - the car engine is started.
Literature
Aksenovich L. A. Physics in secondary school: Theory. Assignments. Tests: Textbook. allowance for institutions providing general education. environment, education / L. A. Aksenovich, N. N. Rakina, K. S. Farino; Ed. K. S. Farino. - Mn.: Adukatsiya i vyakhavanne, 2004. - P.322-323.
A magnetic field is a special form of matter that is created by magnets, conductors with current (moving charged particles) and which can be detected by the interaction of magnets, conductors with current (moving charged particles).
Oersted's experience
The first experiments (carried out in 1820) that showed that there is a deep connection between electrical and magnetic phenomena were the experiments of the Danish physicist H. Oersted.
A magnetic needle located near a conductor rotates through a certain angle when the current in the conductor is turned on. When the circuit is opened, the arrow returns to its original position.
From the experience of G. Oersted it follows that there is a magnetic field around this conductor.
Ampere's experience
Two parallel conductors through which electric current flows interact with each other: they attract if the currents are in the same direction, and repel if the currents are in the opposite direction. This occurs due to the interaction of magnetic fields arising around the conductors.
Properties of magnetic field
1. Materially, i.e. exists independently of us and our knowledge about it.
2. Created by magnets, conductors with current (moving charged particles)
3. Detected by the interaction of magnets, conductors with current (moving charged particles)
4. Acts on magnets, current-carrying conductors (moving charged particles) with some force
5. There are no magnetic charges in nature. You cannot separate the north and south poles and get a body with one pole.
6. The reason why bodies have magnetic properties was found by the French scientist Ampere. Ampere put forward the conclusion that the magnetic properties of any body are determined by closed electric currents inside it.
These currents represent the movement of electrons around orbits in an atom.
If the planes in which these currents circulate are located randomly in relation to each other due to the thermal movement of the molecules that make up the body, then their interactions are mutually compensated and the body does not exhibit any magnetic properties.
And vice versa: if the planes in which the electrons rotate are parallel to each other and the directions of the normals to these planes coincide, then such substances enhance the external magnetic field.
7. Magnetic forces act in a magnetic field in certain directions, which are called magnetic lines of force. With their help, you can conveniently and clearly show the magnetic field in a particular case.
In order to more accurately depict the magnetic field, we agreed in those places where the field is stronger to show the lines of force located denser, i.e. closer to each other. And vice versa, in places where the field is weaker, fewer field lines are shown, i.e. less frequently located.
8. The magnetic field is characterized by the magnetic induction vector.
The magnetic induction vector is a vector quantity characterizing the magnetic field.
The direction of the magnetic induction vector coincides with the direction of the north pole of the free magnetic needle at a given point.
The direction of the field induction vector and current strength I are related by the “right screw (gimlet) rule”:
if you screw in a gimlet in the direction of the current in the conductor, then the direction of the speed of movement of the end of its handle at a given point will coincide with the direction of the magnetic induction vector at that point.
Magnetic field - power field , acting on moving electric charges and on bodies with magnetic moment, regardless of the state of their movement;magnetic component of electromagnetic fields .
Magnetic field lines are imaginary lines, the tangents to which at each point of the field coincide in direction with the magnetic induction vector.
For a magnetic field, the principle of superposition is valid: at each point in space the magnetic induction vector B∑ → B∑→created at this point by all sources of magnetic fields is equal to the vector sum of the magnetic induction vectors Bk→ Bk→created at this point by all sources of magnetic fields:
28. Biot-Savart-Laplace law. Law of total current.
The formulation of Biot-Savart-Laplace's law is as follows: When a direct current passes through a closed loop located in a vacuum, for a point located at a distance r0 from the loop, the magnetic induction will have the form.
where I is the current in the circuit
gamma contour along which integration takes place
r0 arbitrary point
Total current law this is the law connecting the circulation of the magnetic field strength vector and current.
The circulation of the magnetic field strength vector along the circuit is equal to the algebraic sum of the currents covered by this circuit.
29. Magnetic field of a current-carrying conductor. Magnetic moment of circular current.
30. The effect of a magnetic field on a current-carrying conductor. Ampere's law. Interaction of currents .
F = B I l sinα ,
Where α - the angle between the magnetic induction and current vectors,B - magnetic field induction,I - current strength in the conductor,l - length of the conductor.
Interaction of currents. If two wires are connected to a DC circuit, then: Parallel, closely spaced conductors connected in series repel each other. Conductors connected in parallel attract each other.
31. The effect of electric and magnetic fields on a moving charge. Lorentz force.
Lorentz force - strength, with which electromagnetic field according to classical (non-quantum) electrodynamics acts on point charged particle. Sometimes the Lorentz force is called the force acting on a moving object with speed charge only from the outside magnetic field, often full force - from the electromagnetic field in general , in other words, from the outside electrical And magnetic fields.
32. The effect of a magnetic field on matter. Dia-, para- and ferromagnets. Magnetic hysteresis.
B= B 0 + B 1
Where B⃗ B→ - magnetic field induction in matter; B⃗ 0 B→0 - magnetic field induction in vacuum, B⃗ 1 B→1 - magnetic induction of the field arising due to the magnetization of the substance.
Substances for which the magnetic permeability is slightly less than unity (μ< 1), называются diamagnetic materials, slightly greater than unity (μ > 1) - paramagnetic.
ferromagnet - substance or material in which a phenomenon is observed ferromagnetism, i.e., the appearance of spontaneous magnetization at a temperature below the Curie temperature.
Magnetic hysteresis - phenomenon dependencies vector magnetization And vector magnetic strength fields V substance Not only from attached external fields, But And from background of this sample
Magnetic field, what is it? - a special type of matter;
Where does it exist? - around moving electric charges (including around a conductor carrying current)
How to detect? - using a magnetic needle (or iron filings) or by its action on a current-carrying conductor.
Oersted's experience:
The magnetic needle turns if electricity begins to flow through the conductor. current, because A magnetic field is formed around a conductor carrying current.
Interaction of two conductors with current:
Each current-carrying conductor has its own magnetic field around itself, which acts with some force on the neighboring conductor.
Depending on the direction of currents, conductors can attract or repel each other.
Remember last school year:
MAGNETIC LINES (or otherwise magnetic induction lines)
How to depict a magnetic field? - using magnetic lines;
Magnetic lines, what are they?
These are imaginary lines along which magnetic needles placed in a magnetic field are located. Magnetic lines can be drawn through any point in the magnetic field, they have a direction and are always closed.
Remember last school year:
INHOMOGENEOUS MAGNETIC FIELD
Characteristics of a non-uniform magnetic field: magnetic lines are curved; the density of magnetic lines is different; the force with which the magnetic field acts on the magnetic needle is different at different points of this field in magnitude and direction.
Where does a non-uniform magnetic field exist?
Around a straight conductor carrying current;
Around the strip magnet;
Around the solenoid (coil with current).
HOMOGENEOUS MAGNETIC FIELD
Characteristics of a uniform magnetic field: magnetic lines are parallel straight lines; the density of magnetic lines is the same everywhere; The force with which the magnetic field acts on the magnetic needle is the same at all points of this field in magnitude and direction.
Where does a uniform magnetic field exist?
- inside a strip magnet and inside a solenoid, if its length is much greater than its diameter.
INTERESTING
The ability of iron and its alloys to be strongly magnetized disappears when heated to high temperatures. Pure iron loses this ability when heated to 767 °C.
The powerful magnets used in many modern products can interfere with the performance of pacemakers and implanted cardiac devices in cardiac patients. Regular iron or ferrite magnets, easily identified by their dull gray color, are low in strength and cause little to no trouble.
However, very strong magnets have recently appeared - shiny silver in color and an alloy of neodymium, iron and boron. The magnetic field they create is very strong, making them widely used in computer disks, headphones and speakers, as well as toys, jewelry and even clothing.
One day, in the roadstead of the main city of Mallorca, the French warship La Rolaine appeared. Its condition was so pitiful that the ship barely reached the pier under its own power. When French scientists, including twenty-two-year-old Arago, boarded the ship, it turned out that the ship was destroyed by lightning. While the commission examined the ship, shaking their heads at the sight of the burnt masts and superstructures, Arago hurried to the compasses and saw what he expected: the compass arrows were pointing in different directions...
A year later, while digging through the remains of a Genoese ship that crashed near Algeria, Arago discovered that the compass needles were demagnetized. In the pitch darkness of a foggy night, the captain, having directed the ship north on the compass, away from dangerous places, was in fact uncontrollably heading towards what he was trying so hard to avoid . The ship sailed south toward the rocks, deceived by the lightning-struck magnetic compass.
V. Kartsev. Magnet for three millennia.
The magnetic compass was invented in China.
Already 4,000 years ago, caravan riders took a clay pot with them and “took care of it on the road more than all their expensive cargo.” In it, on the surface of the liquid on a wooden float, lay a stone that loves iron. He could turn and all the time pointed travelers towards the south, which, in the absence of the Sun, helped them go to the wells.
At the beginning of our era, the Chinese learned to make artificial magnets by magnetizing an iron needle.
And only a thousand years later Europeans began to use a magnetized compass needle.
EARTH'S MAGNETIC FIELD
The earth is a large permanent magnet.
The South Magnetic Pole, although located, by earthly standards, close to the North Geographic Pole, is nevertheless separated by about 2000 km.
There are areas on the Earth's surface where its own magnetic field is strongly distorted by the magnetic field of iron ores located at shallow depths. One of such territories is the Kursk magnetic anomaly, located in the Kursk region.
The magnetic induction of the Earth's magnetic field is only about 0.0004 Tesla.
___
The Earth's magnetic field is affected by increased solar activity. About once every 11.5 years it increases so much that radio communications are disrupted, the well-being of people and animals worsens, and compass needles begin to “dance” unpredictably from side to side. In this case, they say that a magnetic storm is occurring. It usually lasts from several hours to several days.
The Earth's magnetic field changes its orientation from time to time, performing secular oscillations (lasting 5–10 thousand years), and completely reorienting, i.e. swapping magnetic poles (2–3 times per million years). This is indicated by the magnetic field of distant eras “frozen” into sedimentary and volcanic rocks. The behavior of the geomagnetic field cannot be called chaotic; it obeys a kind of “schedule”.
The direction and magnitude of the geomagnetic field are determined by processes occurring in the Earth's core. The characteristic time of polarity reversal, determined by the inner solid core, is from 3 to 5 thousand years, and determined by the outer liquid core - about 500 years. These times may explain the observed dynamics of the geomagnetic field. Computer modeling, taking into account various intraterrestrial processes, showed the possibility of reversing the polarity of the magnetic field in about 5 thousand years.
Tricks with magnets
“The Temple of Enchantment, or the mechanical, optical and physical office of Mr. Gamuletsky de Colla” by the famous Russian illusionist Gamuletsky, which existed until 1842, became famous, among other things, for the fact that visitors ascending the staircase decorated with candelabra and carpeted with carpets could even notice from afar the At the top of the stairs, a gilded figure of an angel, made in natural human height, which hovered in a horizontal position above the office door without being suspended or supported. Anyone could verify that the figure had no supports. When visitors entered the platform, the angel raised his hand, brought the horn to his mouth and played it, moving his fingers in the most natural way. “For ten years,” said Gamuletsky, “I worked to find the point and weight of the magnet and iron in order to hold the angel in the air. In addition to work and a lot of money, I spent on this miracle.”
In the Middle Ages, a very common illusion act was the so-called “obedient fish” made of wood. They swam in the pool and obeyed the slightest wave of the magician's hand, who made them move in all sorts of directions. The secret of the trick was extremely simple: a magnet was hidden in the magician’s sleeve, and pieces of iron were inserted into the heads of the fish.
Closer to us in time were the manipulations of the Englishman Jonas. His signature act: Jonas invited some spectators to put the watch on the table, after which he, without touching the watch, randomly changed the position of the hands.
The modern embodiment of this idea is electromagnetic couplings, well known to electricians, with which you can rotate devices separated from the engine by some obstacle, for example, a wall.
In the mid-80s of the 19th century, rumors spread about a learned elephant who could not only add and subtract, but even multiply, divide and extract roots. This was done as follows. The trainer, for example, asked the elephant: “What is seven eight?” There was a board with numbers in front of the elephant. After the question, the elephant took the pointer and confidently showed the number 56. Dividing and extracting the square root were done in the same way. The trick was quite simple: a small electromagnet was hidden under each number on the board. When the elephant was asked a question, a current was supplied to the winding of the magnet located to indicate the correct answer. The iron pointer in the elephant's trunk was itself attracted to the correct number. The answer came automatically. Despite the simplicity of this training, the secret of the trick could not be unraveled for a long time, and the “learned elephant” enjoyed enormous success.
