Magnetic induction lines lie in a plane. Magnetic field induction. Magnetic induction lines. Earth's magnetic field. See what "Magnetic induction lines" are in other dictionaries

Already in the 6th century. BC. In China, it was known that some ores have the ability to attract each other and attract iron objects. Pieces of such ores were found near the city of Magnesia in Asia Minor, so they received the name magnets.

How do magnets and iron objects interact? Let's remember why electrified bodies are attracted? Because a peculiar form of matter is formed near an electric charge - an electric field. There is a similar form of matter around the magnet, but it has a different nature of origin (after all, the ore is electrically neutral), it is called magnetic field.

To study the magnetic field, straight or horseshoe magnets are used. Certain places on a magnet have the greatest attractive effect, they are called poles(north and south). Opposite magnetic poles attract, and like magnetic poles repel.

For the strength characteristics of the magnetic field, use magnetic field induction vector B. The magnetic field is graphically represented using lines of force ( magnetic induction lines). Lines are closed, have neither beginning nor end. The place from which magnetic lines emerge is the North Pole; magnetic lines enter the South Pole.

The magnetic field can be made "visible" using iron filings.

Magnetic field of a current-carrying conductor

And now about what we found Hans Christian Oersted And Andre Marie Ampere in 1820. It turns out that a magnetic field exists not only around a magnet, but also around any current-carrying conductor. Any wire, such as a lamp cord, through which electric current flows is a magnet! A wire with current interacts with a magnet (try holding a compass near it), two wires with current interact with each other.

Direct current magnetic field lines are circles around a conductor.

Magnetic induction vector direction

The direction of the magnetic field at a given point can be defined as the direction indicated by the north pole of a compass needle placed at that point.

The direction of the magnetic induction lines depends on the direction of the current in the conductor.

The direction of the induction vector is determined according to the rule gimlet or rule right hand.

Magnetic induction vector

This is a vector quantity characterizing the force action of the field.

Induction of the magnetic field of an infinite straight conductor with current at a distance r from it:

Magnetic field induction at the center of a thin circular coil of radius r:

Magnetic field induction solenoid(a coil whose turns are sequentially passed current in one direction):

Superposition principle

If a magnetic field at a given point in space is created by several field sources, then magnetic induction is the vector sum of the inductions of each field separately

The Earth is not only a large negative charge and a source of electric field, but at the same time the magnetic field of our planet is similar to the field of a direct magnet of gigantic proportions.

Geographic south is close to magnetic north, and geographic north is close to magnetic south. If a compass is placed in the Earth's magnetic field, then its north arrow is oriented along the lines of magnetic induction in the direction of the south magnetic pole, that is, it will show us where the geographic north is located.

The characteristic elements of terrestrial magnetism change very slowly over time - secular changes. However, from time to time magnetic storms occur, when the Earth's magnetic field is greatly distorted for several hours and then gradually returns to its previous values. Such a drastic change affects people's well-being.

The Earth's magnetic field is a "shield" that protects our planet from particles penetrating from space ("solar wind"). Near the magnetic poles, particle flows come much closer to the Earth's surface. During powerful solar flares, the magnetosphere is deformed, and these particles can move into the upper layers of the atmosphere, where they collide with gas molecules, forming auroras.

Iron dioxide particles on magnetic film are highly magnetized during the recording process.

Magnetic levitation trains glide over surfaces with absolutely no friction. The train is capable of reaching speeds of up to 650 km/h.

The work of the brain, the pulsation of the heart is accompanied by electrical impulses. In this case, a weak magnetic field appears in the organs.

Magnetic field is a component of the electromagnetic field that appears in the presence of a time-varying electric field. In addition, a magnetic field can be created by a current of charged particles, or by the magnetic moments of electrons in atoms (permanent magnets).

Magnetic induction-vector quantity, which is the force characteristic of the magnetic field at a given point in space. Shows the force with which the magnetic field acts on a charge moving at speed.

Magnetic induction lines(magnetic field lines) are lines drawn in a magnetic field so that at each point in the field the tangent to the magnetic induction line coincides with the direction of the vector IN at this point in the field.

Magnetic induction lines are most easily observed using small

Needle-shaped iron filings, which are magnetized in the field under study and behave like small magnetic needles (a free magnetic needle rotates in a magnetic field so that the axis of the needle, connecting its south pole with the north, coincides with the direction IN).

The type of magnetic induction lines of the simplest magnetic fields is shown

in Fig. From Fig. b- G it can be seen that these lines enclose a current-carrying conductor that creates a field. Near the conductor they lie in planes perpendicular to the conductor.

N
The direction of the induction lines is determined by gimlet rule: if you screw a gimlet in the direction of the current density vector in a conductor, then the direction of movement of the gimlet handle will indicate the direction of the magnetic induction lines.

Magnetic field lines

The current cannot break at any points, that is, neither begin nor end: they are either closed (Fig. b, c, d), or they endlessly wind around a certain surface, densely filling it everywhere, but never returning a second time to any point on the surface.

Gauss's theorem for magnetic induction

The flux of the magnetic induction vector through any closed surface is zero:

This is equivalent to the fact that in nature there are no “magnetic charges” (monopoles) that would create a magnetic field, just as electric charges create an electric field. In other words, Gauss's theorem for magnetic induction shows that the magnetic field is vortex.

2 Biot-Savart–Laplace law

Let a direct current flow along a contour γ located in a vacuum - the point at which the field is sought, then the induction of the magnetic field at this point is expressed by the integral (in the SI system)

The direction is perpendicular, that is, perpendicular to the plane in which they lie, and coincides with the tangent to the line of magnetic induction. This direction can be found by the rule for finding magnetic induction lines (right screw rule): the direction of rotation of the screw head gives the direction if the translational movement of the gimlet corresponds to the direction of the current in the element. The modulus of the vector is determined by the expression (in SI system)

The vector potential is given by the integral (in the SI system)

The Biot-Savart-Laplace law can be obtained from Maxwell's equations for a stationary field. In this case, the time derivatives are equal to 0, so the equations for the field in vacuum take the form (in the SGS system)

where is the current density in space. In this case, the electric and magnetic fields turn out to be independent. Let's use the vector potential for the magnetic field (in the SGS system):

The gauge invariance of the equations allows us to impose one additional condition on the vector potential:

Expanding the double rotor using the formula of vector analysis, we obtain for the vector potential an equation like the Poisson equation:

Its particular solution is given by an integral similar to the Newtonian potential:

Then the magnetic field is determined by the integral (in the SGS system)

similar in form to the Biot-Savart-Laplace law. This correspondence can be made exact if we use generalized functions and write down the spatial current density corresponding to a coil with current in empty space. Moving from integration over the entire space to a repeated integral along the coil and along planes orthogonal to it and taking into account that

we obtain the Biot - Savart - Laplace law for the field of a coil with current.

Just like electrical ones, they can be represented graphically using magnetic induction lines. An induction line can be drawn through each point of the magnetic field. Since the field induction at any point has a certain direction, the direction of the induction line at each point of a given field can only be unique, which means that the magnetic field lines, as well as the electric field, the magnetic field induction lines are drawn with such density that the number of lines crossing a unit surface perpendicular to them was equal to (or proportional to) the magnetic field induction at a given location. Therefore, by depicting induction lines, you can clearly imagine how induction changes in space, and, consequently, the magnetic field strength in magnitude and direction.

Links

• Visualization of magnetic field lines using metal particles (video).

Wikimedia Foundation. 2010.

See what “Magnetic induction lines” are in other dictionaries:

Lines mentally drawn in a magnetic field so that at any point in the field the magnetic induction vector is directed tangent to the magnetic field passing through this point. L. m. and. post fields electric current cover current-carrying conductors and are either closed,... ...

magnetic induction tube- An area of ​​a magnetic field limited by a continuous surface, the forming parts of which are magnetic induction lines... Polytechnic terminological explanatory dictionary

Electric and magnetic fields, lines whose tangents at each point of the field coincide with the direction of the electric or magnetic field strength, respectively; qualitatively characterize the distribution of the electromagnetic field in... ... encyclopedic Dictionary

This article or section needs revision. Please improve the article in accordance with the rules for writing articles... Wikipedia

Lines drawn in any force field (electric, magnetic, gravitational), the tangents to which at each point in space coincide in direction with the vector characterizing this field (electric or...

Lines mentally drawn in the k.l. force field (electric.. magnetic, gravity) so that at each point of the field the direction of the tangent to the line coincides with the direction of the field strength (magnetic induction in the case of a magnetic field). Through… … Big Encyclopedic Polytechnic Dictionary

path of magnetic field line- magnetic induction line - [Ya.N.Luginsky, M.S.Fezi Zhilinskaya, Yu.S.Kabirov. English-Russian dictionary of electrical engineering and power engineering, Moscow, 1999] Topics electrical engineering, basic concepts Synonyms magnetic induction line EN... ... Technical Translator's Guide

Average length of the magnetic field line of the sample- the length of a uniformly magnetized sample made of the same magnetic material as the test sample, magnetized with the same magnetic field strength as the latter at the same values ​​of magnetic induction, magnetomotive force and... ... Dictionary-reference book of terms of normative and technical documentation

1) Properties of magnets. The most characteristic magnetic phenomenon, the attraction of pieces of iron by a magnet, has been known since ancient times. However, in Europe, until the 12th century, this phenomenon was observed only with natural magnets, that is, with pieces... ... Encyclopedic Dictionary F.A. Brockhaus and I.A. Efron

A force field acting on moving electric charges and on bodies possessing a magnetic moment (See Magnetic moment), regardless of their state of motion. The magnetic field is characterized by the magnetic induction vector B, which determines: ... ... Great Soviet Encyclopedia

29. Coriolis force

The most terrible force that does not need gravitons

First, what does the scientific world know about the Coriolis force?

When the disk rotates, points farther from the center move with a higher tangential speed than points less distant (a group of black arrows along the radius). You can move a body along the radius so that it remains on the radius (blue arrow from position “A” to position “B”) by increasing the speed of the body, that is, giving it acceleration. If frame of reference rotates along with the disk, it is clear that the body “does not want” to remain at the radius, but “tries” to go to the left - this is the Coriolis force.

Trajectories of a ball moving along the surface of a rotating plate in different reference systems (above - in inertial, below - in non-inertial).

Coriolis force- one of inertia forces existing in non-inertial reference system due to rotation and laws of inertia , manifested when moving in a direction at an angle to the axis of rotation. Named after the French scientistGustave Gaspard Coriolis , who first described it. Coriolis acceleration was obtained by Coriolis in 1833, Gauss in 1803 and Euler in 1765.

The reason for the appearance of the Coriolis force is the Coriolis (rotary) acceleration. INinertial reference systems the law of inertia applies , that is, each body tends to move in a straight line and with a constant speed . If we consider the motion of a body, uniform along a certain rotating radius and directed from the center, it becomes clear that in order for it to take place, it is necessary to give the body acceleration , since the farther from the center, the greater the tangential rotation speed should be. This means that from the point of view of the rotating frame of reference, some force will try to displace the body from the radius.

In order for a body to move with Coriolis acceleration, it is necessary to apply a force to the body equal to F = ma, Where a— Coriolis acceleration. Accordingly, the body acts according to Newton's third law with a force in the opposite direction.F K = — ma.

The force that acts from the body will be called the Coriolis force. Coriolis force should not be confused with another force of inertia - centrifugal force , which is directed along radius of the rotating circle. If the rotation occurs clockwise, then a body moving from the center of rotation will tend to leave the radius to the left. If the rotation occurs counterclockwise, then to the right.

Zhukovsky's rule

Additions:

Gimlet rule

Straight wire with current. Current (I) flowing through a wire creates a magnetic field (B) around the wire.Gimlet rule(also, right hand rule) - mnemonic rule for determining the direction of a vectorangular velocity , characterizing the speed of rotation of the body, as well as the vectormagnetic induction B or to determine directioninduced current . Right hand rule Gimlet rule: “If the direction of translational movement gimlet (screw) ) coincides with the direction of the current in the conductor, then the direction of rotation of the gimlet handle coincides with the directionmagnetic induction vector “.

Determines the direction of induced current in a conductor moving in a magnetic field

Right hand rule: “If the palm of the right hand is positioned so that the magnetic field lines enter it, and the bent thumb is directed along the movement of the conductor, then 4 outstretched fingers will indicate the direction of the induction current.”

For solenoid it is formulated as follows: “If you clasp the solenoid with the palm of your right hand so that four fingers are directed along the current in the turns, then the extended thumb will show the direction of the magnetic field lines inside the solenoid.”

Left hand rule

If the charge is moving and the magnet is at rest, then the left hand rule applies to determine the force: “If the left hand is positioned so that the magnetic field induction lines enter the palm perpendicular to it, and the four fingers are directed along the current (along the movement of a positively charged particle or against negatively charged movement), then the thumb placed at 90° will show the direction of the acting Lorentz or Ampere force.”

A MAGNETIC FIELD

PROPERTIES OF (STATIONARY) MAGNETIC FIELD

Permanent (or stationary) A magnetic field is a magnetic field that does not change over time.

1. Magnetic field is created moving charged particles and bodies, current-carrying conductors, permanent magnets.

2. Magnetic field valid on moving charged particles and bodies, on conductors with current, on permanent magnets, on a frame with current.

3. Magnetic field vortex, i.e. has no source.

MAGNETIC FORCES- these are the forces with which current-carrying conductors act on each other.

………………

MAGNETIC INDUCTION

The magnetic induction vector is always directed in the same way as a freely rotating magnetic needle is oriented in a magnetic field.

MAGNETIC INDUCTION LINES - these are lines tangent to which at any point is the magnetic induction vector.

Uniform magnetic field– this is a magnetic field in which at any point the magnetic induction vector is constant in magnitude and direction; observed between the plates of a flat capacitor, inside a solenoid (if its diameter is much smaller than its length) or inside a strip magnet.

PROPERTIES OF MAGNETIC INDUCTION LINES

– have a direction;

– continuous;

– closed (i.e. the magnetic field is vortex);

– do not intersect;

– their density is used to judge the magnitude of magnetic induction.

Gimlet rule(mainly for a straight current-carrying conductor):

	If the direction of translational movement of the gimlet coincides with the direction of the current in the conductor, then the direction of rotation of the gimlet handle coincides with the direction of the magnetic field lines of the current.Right hand rule (mainly to determine the direction of the magnetic lines inside the solenoid):If you clasp the solenoid with the palm of your right hand so that four fingers are directed along the current in the turns, then the extended thumb will show the direction of the magnetic field lines inside the solenoid.
	There are other possible applications of the gimlet and right hand rules.
	AMP POWER is the force with which a magnetic field acts on a current-carrying conductor.The ampere force module is equal to the product of the current strength in the conductor by the magnitude of the magnetic induction vector, the length of the conductor and the sine of the angle between the magnetic induction vector and the direction of the current in the conductor.The Ampere force is maximum if the magnetic induction vector is perpendicular to the conductor.If the magnetic induction vector is parallel to the conductor, then the magnetic field has no effect on the current-carrying conductor, i.e. Ampere's force is zero.Ampere force direction determined by left hand rule:

If the left hand is positioned so that the component of the magnetic induction vector perpendicular to the conductor enters the palm, and 4 extended fingers are directed in the direction of the current, then the thumb bent 90 degrees will show the direction of the force acting on the current-carrying conductor.

Thus, in the magnetic field of a straight conductor with current (it is non-uniform), the frame with current is oriented along the radius of the magnetic line and is attracted or repelled from the straight conductor with current, depending on the direction of the currents.

Direction of the Coriolis force on a rotating Earth.Centrifugal force , acting on a body of mass m, modulo equal to F pr = mb 2 r, where b = omega – angular velocity of rotation and r— distance from the axis of rotation. The vector of this force lies in the plane of the rotation axis and is directed perpendicular to it. Magnitude Coriolis forces , acting on a particle moving with speed relative to a given rotating frame of reference, is given by, where alpha is the angle between the particle velocity vectors and the angular velocity of the reference frame. The vector of this force is directed perpendicular to both vectors and to the right of the body speed (determined bygimlet rule ).

Coriolis force effects: laboratory experiments

Foucault pendulum at the North Pole. The axis of rotation of the Earth lies in the plane of oscillation of the pendulum.Foucault pendulum . An experiment clearly demonstrating the rotation of the Earth was carried out in 1851 by a French physicist Leon Foucault . Its meaning is that the plane of oscillationmathematical pendulum is constant relative to the inertial frame of reference, in this case relative to the fixed stars. Thus, in the reference frame associated with the Earth, the plane of oscillation of the pendulum must rotate. From the point of view of a non-inertial reference frame associated with the Earth, the plane of oscillation of the Foucault pendulum rotates under the influence of the Coriolis force.This effect should be most clearly expressed at the poles, where the period of complete rotation of the pendulum plane is equal to the period of rotation of the Earth around its axis (sidereal day). In general, the period is inversely proportional to the sine of latitude; at the equator, the plane of oscillation of the pendulum is unchanged.

Currently Foucault pendulum successfully demonstrated in a number of science museums and planetariums, in particular in the planetariumSt. Petersburg , planetarium of Volgograd.

There are a number of other experiments with pendulums used to prove the rotation of the Earth. For example, in the Bravais experiment (1851) it was usedconical pendulum . The rotation of the Earth was proven by the fact that the periods of oscillations clockwise and counterclockwise were different, since the Coriolis force in these two cases had a different sign. In 1853 Gauss suggested using a non-mathematical pendulum, like Foucault, a physical , which would make it possible to reduce the size of the experimental setup and increase the accuracy of the experiment. This idea was implemented Kamerlingh Onnes in 1879

Gyroscope– a rotating body with a significant moment of inertia retains angular momentum if there are no strong disturbances. Foucault, who was tired of explaining what happens to a Foucault pendulum not at the pole, developed another demonstration: a suspended gyroscope maintained its orientation, which means it turned slowly relative to the observer.

Deflection of projectiles during gun firing. Another observable manifestation of the Coriolis force is the deflection of the trajectories of projectiles (to the right in the northern hemisphere, to the left in the southern hemisphere) fired in a horizontal direction. From the point of view of the inertial reference frame, for projectiles fired along meridian , this is due to the dependence of the linear speed of rotation of the Earth on geographic latitude: when moving from the equator to the pole, the projectile retains the horizontal component of the speed unchanged, while the linear speed of rotation of points on the earth's surface decreases, which leads to a displacement of the projectile from the meridian in the direction of the rotation of the Earth. If the shot was fired parallel to the equator, then the displacement of the projectile from parallel is due to the fact that the trajectory of the projectile lies in the same plane with the center of the Earth, while points on the earth's surface move in a plane perpendicular to the Earth's axis of rotation.

Deviation of freely falling bodies from the vertical. If the speed of a body has a large vertical component, the Coriolis force is directed to the east, which leads to a corresponding deviation in the trajectory of a body freely falling (without initial speed) from a high tower. When considered in an inertial reference frame, the effect is explained by the fact that the top of the tower relative to the center of the Earth moves faster than the base, due to which the trajectory of the body turns out to be a narrow parabola and the body is slightly ahead of the base of the tower.

This effect was predicted Newton in 1679. Due to the complexity of conducting relevant experiments, the effect could only be confirmed at the end of the 18th - first half of the 19th century (Guglielmini, 1791; Benzenberg, 1802; Reich, 1831).

Austrian astronomer Johann Hagen (1902) carried out an experiment that was a modification of this experiment, where instead of freely falling weights, it was used Atwood's car . This made it possible to reduce the acceleration of the fall, which led to a reduction in the size of the experimental setup and an increase in the accuracy of measurements.

The Eötvös effect. At low latitudes, the Coriolis force when moving along the earth's surface is directed in the vertical direction and its action leads to an increase or decrease in the acceleration of gravity, depending on whether the body is moving west or east. This effect is called Eötvös effect in honor of the Hungarian physicist Roland Eötvös , who experimentally discovered it at the beginning of the 20th century.

Experiments using the law of conservation of angular momentum. Some experiments are based onlaw of conservation of angular momentum : in an inertial reference frame, the magnitude of angular momentum (equal to the product moment of inertia to the angular velocity of rotation) does not change under the influence of internal forces. If at some initial moment of time the installation is stationary relative to the Earth, then the speed of its rotation relative to the inertial reference system is equal to the angular speed of rotation of the Earth. If you change the moment of inertia of the system, then the angular speed of its rotation should change, that is, rotation relative to the Earth will begin. In a non-inertial reference frame associated with the Earth, rotation occurs as a result of the Coriolis force. This idea was proposed by a French scientist Louis Poinsot in 1851

The first such experiment was carried out Hagen in 1910: two weights on a smooth crossbar were installed motionless relative to the surface of the Earth. Then the distance between the loads was reduced. As a result, the installation began to rotate. A German scientist performed an even more demonstrative experiment. Hans Bucca (Hans Bucka) in 1949. A rod approximately 1.5 meters long was installed perpendicular to a rectangular frame. Initially, the rod was horizontal, the installation was motionless relative to the Earth. Then the rod was brought to a vertical position, which led to a change in the moment of inertia of approximately 10 4 times and its rapid rotation with an angular velocity of 10 4 times the Earth's rotation speed.

Funnel in the bath. Since the Coriolis force is very weak, it has a negligible effect on the direction of swirl of water when draining a sink or bathtub, so in general the direction of rotation in the funnel is not related to the rotation of the Earth. However, in carefully controlled experiments it is possible to isolate the effect of the Coriolis force from other factors: in the northern hemisphere the funnel will spin counterclockwise, in the southern hemisphere it will spin counterclockwise (the opposite is true).

Coriolis force effects: phenomena in the surrounding nature

Baer's law. As the St. Petersburg academician first noted Karl Baer in 1857, rivers erode the right bank in the northern hemisphere (the left bank in the southern hemisphere), which consequently turns out to be steeper ( Beer's law ). The explanation for the effect is similar to the explanation for the deflection of projectiles when fired in a horizontal direction: under the influence of the Coriolis force, the water hits the right bank harder, which leads to its blurring, and, conversely, retreats from the left bank.

Cyclone over the southeast coast of Iceland (view from space).Winds: trade winds, cyclones, anticyclones. Atmospheric phenomena are also associated with the presence of the Coriolis force, directed to the right in the northern hemisphere and to the left in the southern hemisphere: trade winds, cyclones and anticyclones. Phenomenon trade winds is caused by uneven heating of the lower layers of the earth's atmosphere in the equatorial zone and in the middle latitudes, leading to air flow along the meridian to the south or north in the northern and southern hemispheres, respectively. The action of the Coriolis force leads to the deflection of air flows: in the northern hemisphere - towards the northeast (northeast trade wind), in the southern hemisphere - towards the southeast (southeast trade wind).

Cyclone called an atmospheric vortex with reduced air pressure in the center. Air masses, tending to the center of the cyclone, under the influence of the Coriolis force, spin counterclockwise in the northern hemisphere and clockwise in the southern hemisphere. Likewise, in anticyclone , where there is a maximum pressure in the center, the presence of the Coriolis force leads to vortex motion clockwise in the northern hemisphere and counterclockwise in the southern hemisphere. In a stationary state, the direction of wind movement in a cyclone or anticyclone is such that the Coriolis force balances the pressure gradient between the center and periphery of the vortex (geostrophic wind ).

Optical experiments

A number of experiments demonstrating the rotation of the Earth are based on Sagnac effect: if a ring interferometer performs a rotational motion, then due to relativistic effects the stripes are shifted by an angle

The gimlet rule in the life of dolphins

However, it is unlikely that dolphins are able to sense this force on such a small scale, writes MIGNews. According to another version of Menger, the fact is that animals swim in one direction in order to stay in a group during the relative vulnerability of half-asleep hours. “When dolphins are awake, they use whistling to stay together,” explains the scientist. “But when they sleep, they don’t want to make noise because they’re afraid of attracting attention.” But Menger doesn't know why the choice of direction changes depending on the hemisphere: “It's beyond me,” admits the researcher.

Amateur's opinion

So, we have the assembly:

1. The Coriolis force is one of the

5. A MAGNETIC FIELD- this is a special type of matter through which interaction occurs between moving electrically charged particles.

6. MAGNETIC INDUCTION- this is the strength characteristic of the magnetic field.

7. DIRECTION OF MAGNETIC INDUCTION LINES- determined by the gimlet rule or the right hand rule.

9. Deviation of freely falling bodies from the vertical.

10. Funnel in the bath

11. Right bank effect.

12. Dolphins.

An experiment with water was conducted at the equator. North of the equator, when draining, the water rotated clockwise, and south of the equator, counterclockwise. The fact that the right bank is higher than the left is because the water drags the rock up.

The Coriolis force has nothing to do with the rotation of the Earth!

A detailed description of communication tubes with satellites, the Moon and the Sun is given in the monograph “Cold Nuclear Fusion”.

There are also effects that arise when the potentials of individual frequencies in communication tubes are reduced.

Effects observed since 2007:

When draining, the water rotated both clockwise and counterclockwise; sometimes the drain was performed without rotation.

Dolphins washed ashore.

There was no current transformation (everything is at the input, nothing at the output).

During transformation, the output power significantly exceeded the input power.

Burning of transformer substations.

Communication system failures.

The gimlet rule did not work for magnetic induction.

The Gulf Stream has disappeared.

Planned:

Stopping ocean currents.

Stopping rivers flowing into the Black Sea.

Stopping the rivers flowing into the Aral Sea.

Stop of the Yenisei.

The elimination of communication tubes will lead to the displacement of the planetary satellites into circular orbits around the Sun, the radius of the orbits will be less than the radius of the orbit of Mercury.

Removing the communication tube with the Sun means extinguishing the corona.

Removing the communication tube with the Moon means eliminating the reproduction of the “golden billion” and “golden million”, while the Moon “moves” away from the Earth by 1,200,000 km.

Topics of the Unified State Examination codifier: interaction of magnets, magnetic field of a conductor with current.

The magnetic properties of matter have been known to people for a long time. Magnets got their name from the ancient city of Magnesia: in its vicinity there was a common mineral (later called magnetic iron ore or magnetite), pieces of which attracted iron objects.

Magnet interaction

On two sides of each magnet there are North Pole And South Pole. Two magnets are attracted to each other by opposite poles and repelled by like poles. Magnets can act on each other even through a vacuum! All this resembles the interaction of electric charges, however the interaction of magnets is not electrical. This is evidenced by the following experimental facts.

Magnetic force weakens as the magnet heats up. The strength of the interaction of point charges does not depend on their temperature.

The magnetic force weakens if the magnet is shaken. Nothing like this happens with electrically charged bodies.

Positive electrical charges can be separated from negative ones (for example, when electrifying bodies). But it is impossible to separate the poles of a magnet: if you cut a magnet into two parts, then poles also appear at the cut site, and the magnet splits into two magnets with opposite poles at the ends (oriented in exactly the same way as the poles of the original magnet).

So magnets Always bipolar, they exist only in the form dipoles. Isolated magnetic poles (called magnetic monopoles- analogues of electric charge) do not exist in nature (in any case, they have not yet been discovered experimentally). This is perhaps the most striking asymmetry between electricity and magnetism.

Like electrically charged bodies, magnets act on electric charges. However, the magnet only acts on moving charge; if the charge is at rest relative to the magnet, then the effect of magnetic force on the charge is not observed. On the contrary, an electrified body acts on any charge, regardless of whether it is at rest or in motion.

According to modern concepts of short-range theory, the interaction of magnets is carried out through magnetic field Namely, a magnet creates a magnetic field in the surrounding space, which acts on another magnet and causes a visible attraction or repulsion of these magnets.

An example of a magnet is magnetic needle compass. Using a magnetic needle, you can judge the presence of a magnetic field in a given region of space, as well as the direction of the field.

Our planet Earth is a giant magnet. Not far from the north geographic pole of the Earth is the south magnetic pole. Therefore, the north end of the compass needle, turning towards the south magnetic pole of the Earth, points to geographic north. This is where the name “north pole” of a magnet came from.

Magnetic field lines

The electric field, we recall, is studied using small test charges, by the effect on which one can judge the magnitude and direction of the field. The analogue of a test charge in the case of a magnetic field is a small magnetic needle.

For example, you can get some geometric insight into the magnetic field by placing very small compass needles at different points in space. Experience shows that the arrows will line up along certain lines - the so-called magnetic field lines. Let us define this concept in the form of the following three points.

1. Magnetic field lines, or magnetic lines of force, are directed lines in space that have the following property: a small compass needle placed at each point on such a line is oriented tangent to this line.

2. The direction of the magnetic field line is considered to be the direction of the northern ends of the compass needles located at points on this line.

3. The denser the lines, the stronger the magnetic field in a given region of space..

Iron filings can successfully serve as compass needles: in a magnetic field, small filings become magnetized and behave exactly like magnetic needles.

So, by pouring iron filings around a permanent magnet, we will see approximately the following picture of magnetic field lines (Fig. 1).

Rice. 1. Permanent magnet field

The north pole of a magnet is indicated by the color blue and the letter ; the south pole - in red and the letter . Please note that the field lines leave the north pole of the magnet and enter the south pole: after all, it is towards the south pole of the magnet that the north end of the compass needle will be directed.

Oersted's experience

Despite the fact that electrical and magnetic phenomena have been known to people since antiquity, no relationship between them was observed for a long time. For several centuries, research into electricity and magnetism proceeded in parallel and independently of each other.

The remarkable fact that electrical and magnetic phenomena are actually related to each other was first discovered in 1820 - in the famous experiment of Oersted.

The diagram of Oersted's experiment is shown in Fig. 2 (image from the site rt.mipt.ru). Above the magnetic needle (and are the north and south poles of the needle) there is a metal conductor connected to a current source. If you close the circuit, the arrow turns perpendicular to the conductor!
This simple experiment directly indicated the relationship between electricity and magnetism. The experiments that followed Oersted's experiment firmly established the following pattern: magnetic field is generated by electric currents and acts on currents.

Rice. 2. Oersted's experiment

The pattern of magnetic field lines generated by a current-carrying conductor depends on the shape of the conductor.

Magnetic field of a straight wire carrying current

The magnetic field lines of a straight wire carrying current are concentric circles. The centers of these circles lie on the wire, and their planes are perpendicular to the wire (Fig. 3).

Rice. 3. Field of a straight wire with current

There are two alternative rules for determining the direction of forward magnetic field lines.

Clockwise rule. The field lines go counterclockwise if you look so that the current flows towards us.

Screw rule(or gimlet rule, or corkscrew rule- this is something closer to someone ;-)). The field lines go where you need to turn the screw (with a regular right-hand thread) so that it moves along the thread in the direction of the current.

Use the rule that suits you best. It is better to get used to the clockwise rule - you will later see for yourself that it is more universal and easier to use (and then remember it with gratitude in your first year, when you study analytical geometry).

In Fig. 3 something new has appeared: this is a vector called magnetic field induction, or magnetic induction. The magnetic induction vector is analogous to the electric field strength vector: it serves power characteristic magnetic field, determining the force with which the magnetic field acts on moving charges.

We will talk about forces in a magnetic field later, but for now we will only note that the magnitude and direction of the magnetic field is determined by the magnetic induction vector. At each point in space, the vector is directed in the same direction as the northern end of the compass needle placed at a given point, namely, tangent to the field line in the direction of this line. Magnetic induction is measured in Tesla(Tl).

As in the case of the electric field, for the magnetic field induction the following applies: superposition principle. It lies in the fact that inductions of magnetic fields created at a given point by various currents add up vectorially and give the resulting vector of magnetic induction:.

Magnetic field of a coil with current

Consider a circular coil through which a direct current circulates. We do not show the source that creates the current in the figure.

The picture of the field lines of our orbit will look approximately as follows (Fig. 4).

Rice. 4. Field of a coil with current

It will be important for us to be able to determine into which half-space (relative to the plane of the coil) the magnetic field is directed. Again we have two alternative rules.

Clockwise rule. The field lines go there, looking from where the current appears to circulate counterclockwise.

Screw rule. The field lines go where the screw (with a normal right-hand thread) will move if rotated in the direction of the current.

As you can see, the current and the field change roles - compared to the formulation of these rules for the case of direct current.

Magnetic field of a current coil

Coil It will work if you wind the wire tightly, turn to turn, into a sufficiently long spiral (Fig. 5 - image from en.wikipedia.org). The coil may have several tens, hundreds or even thousands of turns. The coil is also called solenoid.

Rice. 5. Coil (solenoid)

The magnetic field of one turn, as we know, does not look very simple. Fields? individual turns of the coil are superimposed on each other, and it would seem that the result should be a very confusing picture. However, this is not so: the field of a long coil has an unexpectedly simple structure (Fig. 6).

Rice. 6. current coil field

In this figure, the current in the coil flows counterclockwise when viewed from the left (this will happen if in Fig. 5 the right end of the coil is connected to the “plus” of the current source, and the left end to the “minus”). We see that the magnetic field of the coil has two characteristic properties.

1. Inside the coil, far from its edges, the magnetic field is homogeneous: at each point the magnetic induction vector is the same in magnitude and direction. Field lines are parallel straight lines; they bend only near the edges of the coil when they come out.

2. Outside the coil the field is close to zero. The more turns in the coil, the weaker the field outside it.

Note that an infinitely long coil does not release the field outward at all: there is no magnetic field outside the coil. Inside such a coil, the field is uniform everywhere.

Doesn't remind you of anything? A coil is the “magnetic” analogue of a capacitor. You remember that a capacitor creates a uniform electric field inside itself, the lines of which bend only near the edges of the plates, and outside the capacitor the field is close to zero; a capacitor with infinite plates does not release the field to the outside at all, and the field is uniform everywhere inside it.

And now - the main observation. Please compare the picture of the magnetic field lines outside the coil (Fig. 6) with the magnet field lines in Fig. 1 . It's the same thing, isn't it? And now we come to a question that has probably arisen in your mind for a long time: if a magnetic field is generated by currents and acts on currents, then what is the reason for the appearance of a magnetic field near a permanent magnet? After all, this magnet does not seem to be a conductor with current!

Ampere's hypothesis. Elementary currents

At first it was thought that the interaction of magnets was explained by special magnetic charges concentrated at the poles. But, unlike electricity, no one could isolate the magnetic charge; after all, as we have already said, it was not possible to obtain the north and south poles of a magnet separately - the poles are always present in a magnet in pairs.

Doubts about magnetic charges were aggravated by Oersted's experiment, when it turned out that the magnetic field is generated by electric current. Moreover, it turned out that for any magnet it is possible to select a conductor with a current of the appropriate configuration, such that the field of this conductor coincides with the field of the magnet.

Ampere put forward a bold hypothesis. There are no magnetic charges. The action of a magnet is explained by closed electric currents inside it.

What are these currents? These elementary currents circulate inside atoms and molecules; they are associated with the movement of electrons along atomic orbits. The magnetic field of any body consists of the magnetic fields of these elementary currents.

Elementary currents can be randomly located relative to each other. Then their fields are mutually cancelled, and the body does not exhibit magnetic properties.

But if the elementary currents are arranged in a coordinated manner, then their fields, adding up, reinforce each other. The body becomes a magnet (Fig. 7; the magnetic field will be directed towards us; the north pole of the magnet will also be directed towards us).

Rice. 7. Elementary magnet currents

Ampere's hypothesis about elementary currents clarified the properties of magnets. Heating and shaking a magnet destroys the order of its elementary currents, and the magnetic properties weaken. The inseparability of the poles of the magnet has become obvious: at the point where the magnet is cut, we get the same elementary currents at the ends. The ability of a body to be magnetized in a magnetic field is explained by the coordinated alignment of elementary currents that “turn” properly (read about the rotation of a circular current in a magnetic field in the next sheet).

Ampere's hypothesis turned out to be true - this was shown by the further development of physics. Ideas about elementary currents became an integral part of the theory of the atom, developed already in the twentieth century - almost a hundred years after Ampere’s brilliant guess.