The magnetic effect of the current is manifested in the following phenomena. What is the magnetic effect of current

The electric current in the circuit is always manifested by some of its action. This can be both work in a certain load, and the accompanying action of the current. Thus, by the action of the current, one can judge its presence or absence in a given circuit: if the load is working, there is a current. If a typical current-related phenomenon is observed, there is current in the circuit, etc.

In general, electric current is capable of causing various actions: thermal, chemical, magnetic (electromagnetic), light or mechanical, and various kinds of current actions often appear simultaneously. These phenomena and actions of the current will be discussed in this article.

Thermal effect of electric current

When a direct or alternating electric current passes through a conductor, the conductor heats up. Such heating conductors under different conditions and applications can be: metals, electrolytes, plasma, metal melts, semiconductors, semimetals.

In the simplest case, if, say, an electric current is passed through a nichrome wire, then it will heat up. This phenomenon is used in heating devices: in electric kettles, boilers, heaters, electric stoves, etc. In electric arc welding, the temperature of the electric arc generally reaches 7000 ° C, and the metal melts easily - this is also the thermal effect of the current.

The amount of heat released in the circuit section depends on the voltage applied to this section, the value of the current flowing and on the time of its flow ().

By transforming Ohm's law for a section of the circuit, it is possible to use either voltage or current to calculate the amount of heat, but then it is imperative to know the resistance of the circuit, because it is it that limits the current and causes, in fact, heating. Or, knowing the current and voltage in the circuit, you can just as easily find the amount of heat released.

Chemical action of electric current

Electrolytes containing ions, under the action of a direct electric current - this is the chemical effect of the current. Negative ions (anions) are attracted to the positive electrode (anode) during electrolysis, and positive ions (cations) are attracted to the negative electrode (cathode). That is, the substances contained in the electrolyte, in the process of electrolysis, are released on the electrodes of the current source.

For example, a pair of electrodes is immersed in a solution of a certain acid, alkali or salt, and when an electric current is passed through the circuit, a positive charge is created on one electrode, and a negative charge on the other. The ions contained in the solution begin to be deposited on the electrode with the opposite charge.

For example, during the electrolysis of copper sulfate (CuSO4), copper cations Cu2+ with a positive charge move to a negatively charged cathode, where they receive the missing charge, and become neutral copper atoms, settling on the surface of the electrode. The hydroxyl group -OH will give up electrons at the anode, and oxygen will be released as a result. Positively charged hydrogen cations H+ and negatively charged anions SO42- will remain in solution.

The chemical action of electric current is used in industry, for example, to decompose water into its constituent parts (hydrogen and oxygen). Also, electrolysis allows you to get some metals in their pure form. With the help of electrolysis, a thin layer of a certain metal (nickel, chromium) is coated on the surface - this, etc.

In 1832, Michael Faraday found that the mass m of the substance released on the electrode is directly proportional to the electric charge q that has passed through the electrolyte. If a direct current I is passed through the electrolyte for a time t, then Faraday's first law of electrolysis is valid:

Here the coefficient of proportionality k is called the electrochemical equivalent of the substance. It is numerically equal to the mass of the substance released during the passage of a single electric charge through the electrolyte, and depends on the chemical nature of the substance.

In the presence of an electric current in any conductor (solid, liquid or gaseous), a magnetic field is observed around the conductor, that is, a current-carrying conductor acquires magnetic properties.

So, if a magnet is brought to the conductor through which the current flows, for example, in the form of a magnetic compass needle, then the arrow will turn perpendicular to the conductor, and if the conductor is wound on an iron core and a direct current is passed through the conductor, the core will become an electromagnet.

In 1820, Oersted discovered the magnetic effect of current on a magnetic needle, and Ampere established the quantitative laws of the magnetic interaction of conductors with current.

A magnetic field is always generated by current, that is, by moving electric charges, in particular by charged particles (electrons, ions). Oppositely directed currents repel each other, unidirectional currents attract each other.

Such a mechanical interaction occurs due to the interaction of magnetic fields of currents, that is, it is, first of all, a magnetic interaction, and only then a mechanical one. Thus, the magnetic interaction of currents is primary.

In 1831, Faraday established that a changing magnetic field from one circuit generates a current in another circuit: the generated emf is proportional to the rate of change of the magnetic flux. It is logical that it is the magnetic action of currents that is used to this day in all transformers, and not only in electromagnets (for example, in industrial ones).

In its simplest form, the luminous effect of electric current can be observed in an incandescent lamp, the spiral of which is heated by the current passing through it to white heat and emits light.

For an incandescent lamp, light energy accounts for about 5% of the electricity supplied, the remaining 95% of which is converted into heat.

Fluorescent lamps more efficiently convert current energy into light - up to 20% of electricity is converted into visible light thanks to the phosphor, which receives from an electrical discharge in mercury vapor or in an inert gas such as neon.

The luminous effect of electric current is realized more effectively in light-emitting diodes. When an electric current is passed through the p-n junction in the forward direction, charge carriers - electrons and holes - recombine with the emission of photons (due to the transition of electrons from one energy level to another).

The best light emitters are direct-gap semiconductors (i.e., those that allow direct band-to-band optical transitions), such as GaAs, InP, ZnSe, or CdTe. By varying the composition of semiconductors, it is possible to create LEDs for all possible wavelengths from ultraviolet (GaN) to mid-infrared (PbS). The efficiency of an LED as a light source reaches an average of 50%.

As noted above, each conductor through which an electric current flows forms around itself. Magnetic actions are converted into motion, for example, in electric motors, in magnetic lifting devices, in magnetic valves, in relays, etc.

The mechanical action of one current on another describes Ampère's law. This law was first established by André Marie Ampère in 1820 for direct current. From it follows that parallel conductors with electric currents flowing in one direction attract, and in opposite directions they repel.

Ampère's law is also called the law that determines the force with which a magnetic field acts on a small segment of a current-carrying conductor. The force with which the magnetic field acts on a conductor element with current in a magnetic field is directly proportional to the current in the conductor and the vector product of the conductor length element and magnetic induction.

It is based on this principle, where the rotor plays the role of a frame with a current, oriented in the external magnetic field of the stator with a torque M.

1. What is the magnetic effect of electric current? Explain your answer.

The ability of an electric current passing through conductors of the second kind to generate a magnetic field around these wires

2. How can a compass determine the poles of a magnet? Explain your answer.

The north pole of the arrow is attracted to the south pole of the magnet, the south pole to the north.

3. How can you detect the presence of a magnetic field in space? Explain your answer.

For example, using iron filings. Under the influence of the magnetic field of the current, the iron filings are located around the conductor not randomly, but along a concentric circle.

4. How to use a compass to determine if current flows in a conductor? Explain your answer.

If the compass needle is perpendicular to the wire, then a direct current flows in the wire.

5. Is it possible to cut a magnet so that one of the resulting magnets has only a north pole, and the other has only a south one? Explain your answer.

It is impossible to separate the poles from each other by cutting. Magnetic poles exist only in pairs.

6. How can you find out if there is current in the wire without using an ammeter?

• Using a magnetic needle that reacts to the current in the wire.
• Using a sensitive voltmeter by connecting it to the ends of the wire.

The simplest electrical and magnetic phenomena have been known to people since very ancient times.

Apparently, as early as 600 years BC. e. the Greeks knew that a magnet attracted iron, and rubbed amber attracted light objects, like straws, etc. However, the difference between electric and magnetic attraction was not yet clear; both were considered phenomena of the same nature.

A clear distinction between these phenomena is the merit of the English physician and naturalist William Gilbert (1544-1603), who in 1600 published a book entitled "On the magnet, magnetic bodies and a large magnet - the Earth." With this book, in fact, begins a truly scientific study of electrical and magnetic phenomena. Gilbert described in his book all the properties of magnets that were known in his era, and also outlined the results of his own very important experiments. He pointed out a number of significant differences between electric and magnetic attraction and introduced the word "electricity".

Although after Hilbert the distinction between electrical and magnetic phenomena was already indisputably clear to everyone, nevertheless, a number of facts indicated that, for all their differences, these phenomena are somehow closely and inextricably linked with each other. The most conspicuous were the facts of magnetization of iron objects and remagnetization of magnetic arrows under the influence of lightning. In his work Thunder and Lightning, the French physicist Dominique Francois Arago (1786-1853) describes, for example, such a case. “In July 1681, the Queen ship, which was a hundred miles from the coast, on the high seas, was struck by lightning, which caused significant damage to the masts, sails, etc. When night fell, it turned out from the position of the stars that from three compasses that were on the ship, two, instead of pointing to the north, began to point to the south, and the third began to point to the west. Arago also describes a case where lightning struck a house and strongly magnetized steel knives, forks and other objects in it.

At the beginning of the 18th century, it was already established that lightning, in fact, is a strong electric current going through the air; therefore facts such as those described above might suggest that every electric current has some kind of magnetic property. However, these properties of the current were discovered experimentally, and it was possible to study them only in 1820 by the Danish physicist Hans Christian Oersted (1777-1851).

Oersted's main experiment is shown in Fig. 199. Above the fixed wire 1, located along the meridian, i.e. in the north-south direction, a magnetic needle 2 is suspended on a thin thread (Fig. 199, a). The arrow, as you know, is also installed approximately along the north-south line, and therefore it is located approximately parallel to the wire. But as soon as we close the key and let the current flow through wire 1, we will see that the magnetic needle turns, trying to be set at a right angle to it, that is, in a plane perpendicular to the wire (Fig. 199, b). This fundamental experience shows that in the space surrounding a conductor with current, forces act that cause the movement of a magnetic needle, i.e., forces similar to those that act near natural and artificial magnets. Such forces we will call magnetic forces, just as we call forces acting on electric charges electric.

Rice. 199. Oersted's experiment with a magnetic needle, revealing the existence of a magnetic current field: 1 - wire, 2 - magnetic needle suspended parallel to the wire, 3 - battery of galvanic cells, 4 - rheostat, 5 - key

In ch. II, we introduced the concept of an electric field to denote that special state of space, which manifests itself in the actions of electric forces. In the same way, we will call the magnetic field the state of space, which makes itself felt by the action of magnetic forces. Thus, Oersted's experiment proves that magnetic forces arise in the space surrounding the electric current, i.e., a magnetic field is created.

The first question that Oersted asked himself after he made his remarkable discovery was this: does the substance of the wire affect the magnetic field created by the current? “The connecting wire,” Oersted writes, “may consist of several wires or metal strips. The nature of the metal does not change the result, except, perhaps, in respect of magnitude.

With the same result we used wires of platinum, gold, silver, brass and iron, as well as tin and lead policies and mercury.

Oersted carried out all his experiments with metals, that is, with conductors, in which the conductivity, as we now know, is of an electronic nature. It is not difficult, however, to carry out Oersted's experiment by replacing the metal wire with a tube containing an electrolyte or a tube in which a discharge occurs in a gas. We have already described such experiments in § 40 (Fig. 73) and have seen that although in these cases the electric current is due to the movement of positive and negative ions, its effect on the magnetic needle is the same as in the case of current in a metal conductor. Whatever the nature of the conductor through which the current flows, a magnetic field is always created around the conductor, under the influence of which the arrow turns, trying to become perpendicular to the direction of the current.

Thus, we can assert: around any current there is a magnetic field. We have already mentioned this most important property of the electric current (§ 40), when we spoke in more detail about its other actions - thermal and chemical.

Of the three properties or manifestations of electric current, the most characteristic is the creation of a magnetic field. The chemical effects of current in some conductors - electrolytes - take place, in others - metals - are absent. The heat generated by the current can be greater or less for the same current, depending on the resistance of the conductor. In superconductors, it is even possible to pass current without generating heat (§ 49). But the magnetic field is an inseparable companion of any electric current. It does not depend on any special properties of a particular conductor and is determined only by the strength and direction of the current. Most of the technical applications of electricity are also associated with the presence of a magnetic current field.

The presence of current in the electrical circuit is always manifested by some action. For example, work under a specific load or some accompanying phenomenon. Therefore, it is the action of the electric current that indicates its presence as such in a particular electrical circuit. That is, if the load is working, then the current takes place.

It is known that electric current causes various kinds of actions. For example, these include thermal, chemical, magnetic, mechanical or light. At the same time, various actions of an electric current can manifest themselves simultaneously. We will tell you in more detail about all the manifestations in this material.

thermal phenomenon

It is known that the temperature of the conductor rises when current passes through it. Various metals or their melts, semimetals or semiconductors, as well as electrolytes and plasma act as such conductors. For example, when an electric current is passed through a nichrome wire, it is strongly heated. This phenomenon is used in heating devices, namely: in electric kettles, boilers, heaters, etc. Electric arc welding is characterized by the highest temperature, namely, the heating of the electric arc can reach up to 7,000 degrees Celsius. At this temperature, a slight melting of the metal is achieved.

The amount of heat released directly depends on what voltage was applied to this section, as well as on the electric current and the time it takes to pass through the circuit.

To calculate the amount of heat released, either voltage or current is used. In this case, it is necessary to know the resistance indicator in the electrical circuit, since it is it that provokes heating due to current limitation. Also, the amount of heat can be determined using current and voltage.

chemical phenomenon

The chemical action of the electric current is the electrolysis of ions in the electrolyte. During electrolysis, the anode attaches anions to itself, the cathode - cations.

In other words, during electrolysis, certain substances are released on the electrodes of the current source.

Let's give an example: two electrodes are lowered into an acid, alkaline or saline solution. After that, a current is passed through the electrical circuit, which provokes the creation of a positive charge on one of the electrodes, on the other - a negative one. Ions that are in solution are deposited on an electrode with a different charge.

The chemical action of electric current is used in industry. So, using this phenomenon, water is decomposed into oxygen and hydrogen. In addition, by means of electrolysis, metals are obtained in their pure form, and the surface is also electroplated.

magnetic phenomenon

An electric current in a conductor of any state of aggregation creates a magnetic field. In other words, a conductor with an electric current is endowed with magnetic properties.

Thus, if a magnetic compass needle is brought closer to the conductor in which the electric current flows, then it will begin to turn and take a perpendicular position to the conductor. If, however, this conductor is wound on an iron core and a direct current is passed through it, then this core will take on the properties of an electromagnet.

The nature of a magnetic field is always the presence of an electric current. Let us explain: moving charges (charged particles) form a magnetic field. In this case, currents of the opposite direction repel, and currents of the same direction attract. This interaction is justified by the magnetic and mechanical interaction of magnetic fields of electric currents. It turns out that the magnetic interaction of currents is paramount.

Magnetic action is used in transformers and electromagnets.

light phenomenon

The simplest example of a light action is an incandescent lamp. In this light source, the spiral reaches the desired temperature value by means of a current passing through it to a state of white heat. This is how light is emitted. In a traditional incandescent light bulb, only five percent of all electricity is spent on light, while the rest of the lion's share is converted into heat.

More modern counterparts, such as fluorescent lamps, most efficiently convert electricity into light. That is, about twenty percent of all energy is the basis of light. The phosphor receives UV radiation coming from the discharge, which occurs in mercury vapor or inert gases.

The most effective implementation of the light action of the current occurs in. An electric current passing through a pn junction provokes the recombination of charge carriers with the emission of photons. The best led light emitters are direct gap semiconductors. By changing the composition of these semiconductors, it is possible to create LEDs for different light waves (of different lengths and ranges). The efficiency of the LED reaches 50 percent.

mechanical phenomenon

Recall that a magnetic field arises around a conductor with an electric current. All magnetic actions are converted into motion. Examples are electric motors, magnetic lifting installations, relays, etc.

In 1820, André Marie Ampère deduced the well-known "Ampère's Law", which just describes the mechanical action of one electric current on another.

This law states that parallel conductors with an electric current of the same direction experience attraction to each other, and the opposite direction, on the contrary, repulsion.

Also, the ampere law determines the magnitude of the force with which the magnetic field acts on a small segment of the conductor with electric current. It is this force that underlies the functioning of an electric motor.

In the section on the question of physics. 8th grade. a magnetic field. helpee... given by the author petitioner the best answer is 1-a Magnetic action of electric current - the ability of an electric current passing through conductors of the second kind to generate a magnetic field around these wires.
1-b Positive attracts negative 🙂
2-a Hand begins to deviate from normal position
2-b Like-named repel, unlike-named attract
3-a In a magnetic field, the compass needle turns in a strictly defined way, always parallel to the field lines. (rule of gimlet or left hand)
3-b In both cases at the ends
4-a You can use a screwdriver or short circuit (not the best way)
4-b North magnetic is on the south geographic, and vice versa. There is no exact definition - they are subject to displacement
5-a Heating the conductor
5-b Definitely not
6 Amber with a magnet - brothers?
It turned out that this is close to the truth, and their lightning “brothered”. Indeed, when amber is electrified, sparks arise, and sparks are small lightning.
But lightning is lightning, and what does the magnet have to do with it? It was the lightning that turned out to be what united the amber and the magnet, previously "separated" by Gilbert. Here are three excerpts from a description of a lightning strike that show a close connection between the electricity of amber and the attraction of a magnet.
“... In July 1681, the Quick ship was struck by lightning. When night fell, it turned out, according to the position of the stars, that out of the three compasses ... two, instead of pointing north, as before, pointed south, the former northern end of the third compass was directed to the west.
“... In June 1731, a merchant from Wexfield placed in the corner of his room a large box filled with knives, forks and other items made of iron and steel ... Lightning entered the house precisely through this corner in which the box stood, broke it and scattered all the things that were in it. All those forks and knives… turned out to be highly magnetized…”
“... A strong thunderstorm passed in the village of Medvedkovo; the peasants saw how lightning struck a knife, after a thunderstorm the knife began to attract iron nails ... "
Lightning strikes, magnetizing axes, pitchforks, knives, other steel objects, demagnetizing or remagnetizing compass needles, were observed so often that scientists began to look for a connection between electric sparks and magnetism. But neither the passage of current through the iron rods, nor the impact on them of sparks from Leyden jars gave tangible results - the iron was not magnetized, although accurate modern instruments would probably feel this.
The compass needle deviated slightly in the experiments of the physicist Romagnosi from the city of Trent, when he brought the compass closer to the voltaic column - an electric battery. And then only when a current was flowing through the voltaic column. But Romagnosi then did not understand the reasons for this behavior of the compass needle.
The honor of discovering the connection between electricity and magnetism fell to the Danish physicist Hans Christian Oersted (1777-1851), and even then by accident. It happened on February 15, 1820, that's how. Oersted was giving a lecture on physics that day to students at the University of Copenhagen. The lecture was devoted to the thermal effect of current, in other words, the heating of conductors through which electric current flows. Now this phenomenon is used all the time - in electric stoves, irons, boilers, even in electric lamps, the spiral of which is white-hot by current. And in the time of Oersted, such heating of a conductor by current was considered a new and interesting phenomenon.
6-b Insert the core