What is a magnet for children. Encyclopedia of Magnetism - What is Magnetism

Are you, of course, familiar with the subject that is drawn here? This is a magnet. Take such a "horseshoe", bring it to a pin or a nail, and they themselves will jump towards you.

It has long been believed that there is some kind of incomprehensible attachment between a magnet and iron objects. In some languages, the magnet is still called the "loving stone". For many centuries they showed experiments with natural magnets - pieces of magnetic iron ore, but no one could explain the reason for their “love” for everything iron. The only benefit that a magnet then brought was that a compass was made from it: a movable magnetic needle always points north at one end, south at the other (which is why the ends or poles of the magnet were called north and south). The figure shows how to make sure that opposite poles of magnets attract and like poles repel, just like electric charges.

Studying the magnet, they tried to divide it into parts in order to separate the poles. But nothing came out. Any, the smallest piece always turned out to be a whole magnet with two poles. Why did it happen? Electricity helped to understand this.

You may have seen in the movies how steel parts of machines are transferred at the factory. From above, a thick round plate is lowered on chains, to which a bunch of parts stick. Then the plate with the details is lifted and transferred to the right place.

This is an electromagnet. Its main part is an iron coil of wire. A current is passed through the wire, and the coil becomes a magnet.

The coil of an electromagnet is wound with many turns of wire. But if you take just one turn and pass a current through it, you will also get an electromagnet, only a weak one. Even weaker, very tiny electromagnets, it turns out, are in everyone.

The one that revolves around the nucleus is, as it were, an insignificant coil with current, which means it is a tiny magnet with two poles. There are other charged particles in the atom - protons. They also move and also form magnets.

But, - everyone will ask, - if there are magnets in any atom, then all substances must be magnets, and not just iron.

It turns out that the whole point is how these tiny magnets are located. They need to be "disciplined" so that they can all turn in the same direction and keep the correct formation. Only then can matter become a magnet.

Only a few metals, and especially iron, have such qualities. And recently, new, very strong magnets have appeared. They are even better than iron ones, although they are not made of metals, but of ferrites. If you ever hear this word, then know that it means new artificial magnetic substances.

If all the magnets suddenly disappeared, the power plant would stop working, the radio would go silent, the TVs would go out, the telephone would not work, electric locomotives, metro, trams, trolleybuses, cars and buses would stop. Electronic devices and machines could not work, all modern technology would not work. This is the role that magnets play in people's lives.

Each held a magnet in their hands and played with it as a child. Magnets can be very different in shape, size, but all magnets have common property- they attract iron. It seems that they themselves are made of iron, in any case, from some kind of metal for sure. There are, however, "black magnets" or "stones", they also strongly attract pieces of iron, and especially each other.

But they do not look like metal, they break easily, like glass. There are many useful things in the household of magnets, for example, it is convenient to “pin” paper sheets to iron surfaces with their help. It is convenient to collect lost needles with a magnet, so, as we can see, this is a completely useful thing.

Science 2.0 - Big Leap Forward - Magnets

Magnet in the past

Even the ancient Chinese knew about magnets more than 2000 years ago, at least that this phenomenon can be used to choose the direction when traveling. That is, they invented a compass. Philosophers in ancient greece, curious people, collecting various amazing facts, encountered magnets in the vicinity of the city of Magness in Asia Minor. There they found strange stones that could attract iron. For those times, it was no less amazing than aliens could become in our time.

It seemed even more surprising that magnets attract far from all metals, but only iron, and iron itself is capable of becoming a magnet, although not so strong. We can say that the magnet attracted not only iron, but also the curiosity of scientists, and strongly moved forward such a science as physics. Thales of Miletus wrote about the "soul of the magnet", and the Roman Titus Lucretius Carus wrote about the "raging movement of iron filings and rings" in his essay On the Nature of Things. Already he could notice the presence of two poles at the magnet, which later, when the sailors began to use the compass, received names in honor of the cardinal points.

What is a magnet. In simple words. A magnetic field

Take the magnet seriously

The nature of magnets could not be explained for a long time. With the help of magnets, new continents were discovered (sailors still treat the compass with great respect), but no one knew anything about the very nature of magnetism. Work was carried out only to improve the compass, which was also done by the geographer and navigator Christopher Columbus.

In 1820, the Danish scientist Hans Christian Oersted made major discovery. He established the action of a wire with an electric current on a magnetic needle, and, as a scientist, found out by experiments how this happens under different conditions. In the same year, the French physicist Henri Ampere came up with a hypothesis about elementary circular currents flowing in the molecules of a magnetic substance. In 1831, the Englishman Michael Faraday, using a coil of insulated wire and a magnet, conducts experiments showing that mechanical work can be converted into electric current. He also establishes the law of electromagnetic induction and introduces the concept of "magnetic field".

Faraday's law establishes the rule: for a closed circuit, the electromotive force is equal to the rate of change of the magnetic flux passing through this circuit. All electrical machines work on this principle - generators, electric motors, transformers.

In 1873, Scottish scientist James C. Maxwell brings together magnetic and electrical phenomena into one theory, classical electrodynamics.

Substances that can be magnetized are called ferromagnets. This name connects magnets with iron, but besides it, the ability to magnetize is also found in nickel, cobalt, and some other metals. Since the magnetic field has already passed into the region practical use, then magnetic materials have become the subject of great attention.

Experiments began with alloys of magnetic metals and various additives in them. The resulting materials were very expensive, and if Werner Siemens had not come up with the idea to replace the magnet with steel magnetized by a relatively small current, the world would never have seen an electric tram and Siemens. Siemens was also involved in telegraph machines, but here he had many competitors, and the electric tram gave the company a lot of money, and ultimately pulled everything else with it.

Electromagnetic induction

Basic quantities associated with magnets in engineering

We will be interested mainly in magnets, that is, ferromagnets, and leave a little aside the rest, a very vast field of magnetic (better to say, electromagnetic, in memory of Maxwell) phenomena. Our units of measurement will be those accepted in SI (kilogram, meter, second, ampere) and their derivatives:

l Field strength, H, A/m (amps per meter).

This value characterizes the field strength between parallel conductors, the distance between which is 1 m, and the current flowing through them is 1 A. The field strength is a vector quantity.

l Magnetic induction, B, Tesla, magnetic flux density (Weber/m.sq.)

This is the ratio of the current through the conductor to the circumference, on the radius at which we are interested in the magnitude of the induction. The circle lies in the plane that the wire crosses perpendicularly. This includes another factor called magnetic permeability. This is a vector quantity. If we mentally look at the end of the wire and assume that the current flows in the direction away from us, then the magnetic force circles “rotate” clockwise, and the induction vector is applied to the tangent and coincides with them in direction.

l Magnetic permeability, μ (relative value)

If we take the magnetic permeability of the vacuum as 1, then for the rest of the materials we get the corresponding values. So, for example, for air we get a value that is practically the same as for vacuum. For iron, we will obtain substantially larger values, so that we can figuratively (and very accurately) say that iron “draws” magnetic lines of force into itself. If the field strength in a coil without a core is H, then with a core we get μH.

l Coercive force, A/m.

The coercive force indicates how much a magnetic material resists demagnetization and remagnetization. If the current in the coil is completely removed, then there will be residual induction in the core. To make it equal to zero, you need to create a field of some intensity, but the opposite, that is, put the current into reverse direction. This tension is called the coercive force.

Since magnets are always used in practice in some connection with electricity, it should not be surprising that such an electrical quantity as an ampere is used to describe their properties.

From what has been said, it follows that, for example, a nail, which has been acted upon by a magnet, itself becomes a magnet, albeit a weaker one. In practice, it turns out that even children who play with magnets know about it.

There are different requirements for magnets in engineering, depending on where these materials go. Ferromagnetic materials are divided into "soft" and "hard". The first go to the manufacture of cores for devices where the magnetic flux is constant or variable. You cannot make a good independent magnet from soft materials. They demagnetize too easily, and here this is just their valuable property, since the relay must “release” if the current is turned off, and the electric motor must not heat up - excess energy is consumed for remagnetization, which is released in the form of heat.

WHAT DOES A MAGNETIC FIELD REALLY LOOK LIKE? Igor Beletsky

Permanent magnets, that is, those that are called magnets, require hard materials for their manufacture. Rigidity is meant magnetic, that is, a large residual induction and a large coercive force, since, as we have seen, these quantities are closely related. Carbon, tungsten, chromium and cobalt steels are used for such magnets. Their coercive force reaches values of about 6500 A/m.

There are special alloys called alni, alnisi, alnico and many others, as you might guess, they include aluminum, nickel, silicon, cobalt in various combinations, which have a greater coercive force - up to 20,000 ... 60,000 A / m. Such a magnet is not so easy to tear off from iron.

There are magnets specifically designed to operate at higher frequencies. This is the well-known "round magnet". It is “mined” from a worthless speaker from a music center speaker, or a car radio or even a TV of yesteryear. This magnet is made by sintering iron oxides and special additives. Such a material is called ferrite, but not every ferrite is specially magnetized in this way. And in speakers it is used for reasons of reducing useless losses.

Magnets. discovery. How it works?

What happens inside a magnet?

Due to the fact that the atoms of matter are a kind of "clumps" of electricity, they can create their own magnetic field, but only in some metals that have a similar atomic structure, this ability is very pronounced. And iron, and cobalt, and nickel are in periodic system Mendeleev nearby, and have similar structures of electron shells, which turns the atoms of these elements into microscopic magnets.

Since metals can be called a frozen mixture of various crystals of a very small size, it is clear that such alloys can have a lot of magnetic properties. Many groups of atoms can "unroll" their own magnets under the influence of neighbors and external fields. Such "communities" are called magnetic domains, and form very bizarre structures that are still being studied with interest by physicists. This is of great practical importance.

As already mentioned, magnets can be almost atomic in size, so the smallest size of the magnetic domain is limited by the size of the crystal in which the atoms of the magnetic metal are embedded. This explains, for example, the almost fantastic recording density on modern computer hard disks, which, apparently, will continue to grow until the disks have more serious competitors.

Gravity, magnetism and electricity

Where are magnets used?

The cores of which are magnets of magnets, although they are usually referred to simply as cores, magnets have many more uses. There are stationery magnets, furniture door magnets, chess magnets for travelers. These are well-known magnets.

Rarer types include magnets for particle accelerators, these are very impressive structures that can weigh tens of tons or more. Although now experimental physics is overgrown with grass, with the exception of the part that immediately brings super profits on the market, and itself costs almost nothing.

Another curious magnet is installed in a fancy medical device called a magnetic resonance imaging scanner. (Actually, the method is called NMR, nuclear magnetic resonance, but in order not to frighten the people who are generally not strong in physics, it was renamed.) The device requires the placement of the observed object (patient) in a strong magnetic field, and the corresponding magnet has a frightening size and the shape of the devil's coffin.

A person is placed on a couch and rolled through a tunnel in this magnet while sensors scan the place of interest to doctors. In general, it's okay, but for some, claustrophobia comes to the point of panic. Such people will willingly allow themselves to be cut alive, but will not agree to an MRI examination. However, who knows how a person feels in an unusually strong magnetic field with an induction of up to 3 Tesla, after paying good money for it.

To obtain such a strong field, superconductivity is often used by cooling the magnet coil with liquid hydrogen. This makes it possible to “pump up” the field without fear that heating the wires with a strong current will limit the capabilities of the magnet. It's not a cheap setup. But magnets made from special alloys that do not require current biasing are much more expensive.

Our Earth is also a large, although not very strong magnet. It helps not only the owners of the magnetic compass, but also saves us from death. Without it, we would be killed by solar radiation. Painting magnetic field The Earth, modeled by computers from observations from space, looks very impressive.

Here is a small answer to the question about what a magnet is in physics and technology.

The unique properties of certain substances have always surprised people with their unusualness. Particular attention was drawn to the ability of some metals and stones to repel or attract each other. Throughout all epochs, this aroused the interest of the sages and the great surprise of ordinary people.

Starting from the 12th - 13th centuries, it began to be actively used in the production of compasses and other innovative inventions. Today you can see the prevalence and diversity of magnets in all areas of our lives. Every time we see another magnet product, we often ask ourselves the question: “So how are magnets made?”

Types of magnets

There are several types of magnets:

Constant;
Temporary;
Electromagnet;

The difference between the first two magnets lies in their degree of magnetization and the time the field is held inside. Depending on the composition, the magnetic field will be weaker or stronger and more resistant to external fields. An electromagnet is not a real magnet, it's just the effect of electricity that creates a magnetic field around a metal core.

Interesting fact: for the first time, research on this substance was carried out by our domestic scientist Peter Peregrin. In 1269, he published The Book of the Magnet, which described the unique properties of matter and its interaction with the outside world.

What are magnets made of?

For the production of permanent and temporary magnets, iron, neodymium, boron, cobalt, samarium, alnico and ferrites are used. They are crushed in several stages and melted together, baked or pressed together until a permanent or temporary magnetic field is obtained. Depending on the type of magnets and the required characteristics, the composition and proportions of the components change.

Where in ancient times deposits of magnetite were discovered.

The simplest and smallest magnet can be considered an electron. The magnetic properties of all other magnets are due to the magnetic moments of the electrons inside them. From the point of view of quantum field theory, the electromagnetic interaction is carried by a massless boson - a photon (a particle that can be represented as a quantum excitation of an electromagnetic field).

Weber- a magnetic flux, when it decreases to zero, in a circuit coupled to it with a resistance of 1 ohm, an amount of electricity passes 1 coulomb.

Henry- international unit of inductance and mutual induction. If the conductor has an inductance of 1 H and the current in it uniformly changes by 1 A per second, then an EMF of 1 volt is induced at its ends. 1 henry = 1.00052 10 9 absolute electromagnetic units of inductance.

Tesla- a unit of measurement of the magnetic field induction in SI, numerically equal to the induction of such a homogeneous magnetic field, in which a force of 1 newton acts on 1 meter of the length of a straight conductor perpendicular to the magnetic induction vector, with a current of 1 ampere.

Use of magnets

Magnetic media: VHS cassettes contain reels of magnetic tape. Video and audio information is encoded on the magnetic coating on the tape. Also in computer floppy disks and hard disks, data is recorded on a thin magnetic coating. However, storage media are not strictly magnets, as they do not attract objects. Magnets in hard drives are used in the drive and positioning motors.
Credit, debit, and ATM cards all have a magnetic stripe on one side. This band encodes the information needed to connect to a financial institution and link to their accounts.
Conventional televisions and computer monitors: Televisions and computer monitors containing a cathode ray tube use an electromagnet to control the electron beam and form an image on the screen. Plasma panels and LCD displays use other technologies.
Loudspeakers and microphones: Most loudspeakers use a permanent magnet and a current coil to convert electrical energy(signal) in mechanical energy(movement that creates sound). The winding is wound on a coil, attached to the diffuser and an alternating current flows through it, which interacts with the field of a permanent magnet.
Another example of the use of magnets in sound engineering is in the pickup head of an electrophone and in cassette recorders as an economical erasing head.

Heavy Mineral Magnetic Separator

Electric motors and generators: Some electric motors (like loudspeakers) are based on a combination of an electromagnet and a permanent magnet. They convert electrical energy into mechanical energy. A generator, on the other hand, converts mechanical energy into electrical energy by moving a conductor through a magnetic field.
Transformers: devices for transmitting electrical energy between two windings of wire that are electrically isolated but magnetically coupled.
Magnets are used in polarized relays. Such devices remember their state at the time of power off.
Compasses: A compass (or nautical compass) is a magnetized pointer that is free to rotate and orients itself to the direction of a magnetic field, most commonly the Earth's magnetic field.
Art: Vinyl magnetic sheets can be attached to paintings, photographs and other decorative items, allowing them to be attached to refrigerators and other metal surfaces.

Magnets are often used in toys. M-TIC uses magnetic bars connected to metal spheres

Egg-shaped rare earth magnets that attract each other

Toys : Given their ability to resist gravity on close range, magnets are often used in children's toys with fun effects.
Magnets can be used to make jewelry. Necklaces and bracelets may have a magnetic closure, or may be made entirely from a series of linked magnets and black beads.
Magnets can pick up magnetic objects (iron nails, staples, tacks, paper clips) that are either too small, hard to reach, or too thin to hold with your fingers. Some screwdrivers are specially magnetized for this purpose.
Magnets can be used in scrap metal processing to separate magnetic metals (iron, steel and nickel) from non-magnetic metals (aluminum, non-ferrous alloys, etc.). The same idea can be used in the so-called "Magnetic Test", in which the car body is inspected with a magnet to identify areas repaired using fiberglass or plastic putty.
Maglev: A maglev train driven and controlled by magnetic forces. Such a train, unlike traditional trains, does not touch the rail surface during movement. Since there is a gap between the train and the running surface, friction is eliminated, and the only braking force is the aerodynamic drag force.
Magnets are used in fixing furniture doors.
If magnets are placed in sponges, then these sponges can be used to wash thin sheet non-magnetic materials from both sides at once, and one side may be difficult to reach. It can be, for example, the glass of an aquarium or a balcony.
Magnets are used to transmit torque "through" a wall, which can be, for example, a hermetically sealed motor container. So the toy of the GDR "Submarine" was arranged. In the same way, in household water meters, rotation is transmitted from the sensor blades to the counting unit.
Magnets together with a reed switch are used in special position sensors. For example, in refrigerator door sensors and burglar alarms.
Magnets in conjunction with a Hall sensor are used to determine the angular position or angular velocity of the shaft.
Magnets are used in spark gaps to speed up arc quenching.
Magnets are used in non-destructive testing by magnetic particle method (MPC)
Magnets are used to deflect beams of radioactive and ionizing radiation, such as in camera surveillance.
Magnets are used in indicating devices with a deviating needle, such as an ammeter. Such devices are very sensitive and linear.
Magnets are used in microwave valves and circulators.
Magnets are used as part of the deflecting system of cathode ray tubes to adjust the trajectory of the electron beam.
Before the discovery of the law of conservation of energy, there were many attempts to use magnets to build a "perpetual motion machine". People were attracted by the seemingly inexhaustible energy of the magnetic field of a permanent magnet, which have been known for a very long time. But the working layout was never built.
Magnets are used in the construction of non-contact brakes consisting of two plates, one is a magnet, and the other is made of aluminum. One of them is rigidly fixed on the frame, the other rotates with the shaft. Braking is regulated by the gap between them.

Magnetic toys

Uberorbs
Magnetic constructor
Magnetic drawing board
Magnetic letters and numbers
Magnetic checkers and chess

Medicine and security issues

Due to the fact that human tissues are very low level susceptibility to a static magnetic field, there is no scientific evidence of its effectiveness for use in the treatment of any disease. For the same reason, there is no scientific evidence of a human health hazard associated with exposure to this field. However, if the ferromagnetic foreign body located in human tissues, the magnetic field will interact with it, which can be a serious hazard.

Magnetization

Demagnetization

Sometimes the magnetization of materials becomes undesirable and it becomes necessary to demagnetize them. Demagnetization of materials is achieved in various ways:

heating a magnet above the Curie temperature always leads to demagnetization;
place the magnet in an alternating magnetic field that exceeds the coercive force of the material, and then gradually reduce the effect of the magnetic field or remove the magnet from it.

The latter method is used in industry for degaussing tools, hard drives, erasing information on magnetic cards, and so on.

Partial demagnetization of materials occurs as a result of impacts, since a sharp mechanical action leads to domain disordering.