What is the manifestation of the magnetic effect of the current. Actions of electric current: thermal, chemical, magnetic, light and mechanical Why is the magnetic action of electric current considered to be the main

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

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

Thermal effect of electric current

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

In the simplest case, if, say, an electric current is passed through a nichrome wire, it will heat up. This phenomenon is used in heating devices: in electric kettles, in boilers, in 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 a section of the circuit depends on the voltage applied to this section, the value of the flowing current and the time of its flow ().

Having transformed Ohm's law for a section of a circuit, you can 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, in fact, causes heating. Or, knowing the current and voltage in the circuit, you can just as easily find the amount of heat generated.

Chemical action of electric current

Electrolytes containing ions under the influence of a constant electric current - this is the chemical action 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 are released during electrolysis at 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 the negatively charged cathode, where they receive the missing charge, and become neutral copper atoms, settling on the electrode surface. The hydroxyl group -OH will donate electrons at the anode, and oxygen will be released as a result. Positively charged hydrogen cations H + and negatively charged SO42- anions 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. Using electrolysis, they cover the surface with a thin layer of a certain metal (nickel, chromium) - this, etc.

In 1832, Michael Faraday found that the mass m of a substance released on an electrode is directly proportional to the electric charge q passed through the electrolyte. If a constant current I is passed through the electrolyte for a time t, then the first Faraday 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 a substance released when a single electric charge passes 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, the conductor with current acquires magnetic properties.

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

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

The magnetic field is always generated by current, that is, moving electric charges, in particular - charged particles (electrons, ions). Oppositely directed currents are mutually repelled, unidirectional currents are mutually attracted.

Such mechanical interaction occurs due to the interaction of magnetic fields of currents, that is, it is, first of all, magnetic interaction, and only then - mechanical. 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 light effect of an 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 supplied electricity, 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 a phosphor that receives from an electric discharge in mercury vapor or in an inert gas such as neon.

The light effect of electric current is more efficiently realized in LEDs. When an electric current is passed through the pn 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 (that is, those in which direct optical transitions of the zone-to-band are allowed), for example, GaAs, InP, ZnSe or CdTe. By varying the composition of semiconductors, LEDs can be created for all kinds of wavelengths from ultraviolet (GaN) to mid-infrared (PbS). The efficiency of the 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 turn 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 is described by Ampere's law. This law was first established by André Marie Ampere in 1820 for direct current. It follows that parallel conductors with electric currents flowing in one direction are attracted, and in opposite directions they are repelled.

Ampere's law is also called the law that determines the force with which a magnetic field acts on a small segment of a conductor with a current. The force with which a magnetic field acts on an element of a conductor with a current in a magnetic field is directly proportional to the current in the conductor and the vector product of the element of the length of the conductor and the 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 by the torque M.

In the section on the question of physics. 8th grade. a magnetic field. helpeeee ... given by the author Petitioner the best answer is 1-a The magnetic effect of an electric current is 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 to negative 🙂
2-a Pointer starts to deviate from the normal position
2-b Like names repel, unlike attracts
3-a In a magnetic field, the compass needle turns in a strictly defined way, always parallel to the field lines of force. (gimbal or left hand rule)
3-b In both cases at the ends
4-a With a screwdriver, or by closing (not the best way)
4-b North magnetic is located on the southern geographic, and vice versa. No precise definition - subject to displacement
5-a Heating the conductor
5-b Definitely no
6-a Amber with a magnet - brothers?
It turned out that this is close to the truth, and the lightning "framed" them. After all, 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 lightning that turned out to be what brought together the amber and the magnet, previously "separated" by Hilbert. Here are three extracts from a description of a lightning strike that show the close connection between the electricity of amber and the attraction of a magnet.
“... In July 1681 the ship“ Quick ”was struck by lightning. When night fell, it turned out by the position of the stars that of the three compasses ... two, instead of pointing north, as before, pointed to the 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 objects made of iron and steel ... scattered all the things that were in it. All these forks and knives ... turned out to be highly magnetized ... "
“… In the village of Medvedkovo a strong thunderstorm has passed; the peasants saw how lightning struck the knife, after a thunderstorm the knife began to attract iron nails ... "
Lightning strikes, magnetizing axes, pitchforks, knives, and other steel objects, demagnetizing or remagnetizing compass arrows, were observed so often that scientists began to look for a connection between electric sparks and magnetism. But neither passing current through the iron rods, nor the effect of sparks from Leyden cans on them yielded tangible results - the iron was not magnetized, although accurate modern devices would probably feel it.
The compass needle slightly deviated in the experiments of the physicist Romagnosi from the city of Trent, when he brought the compass closer to a voltaic pole - 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 lot of the Danish physicist Hans Christian Oersted (1777-1851), and even then by accident. It happened on February 15, 1820 as follows. Oersted that day gave a lecture on physics to students at the University of Copenhagen. The lecture was devoted to the thermal action of the current, in other words, the heating of the conductors through which the 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 with current. And in the time of Oersted, such heating of a conductor by current was considered a new and interesting phenomenon.
6-b Insert core

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

Apparently, already 600 years BC. NS. the Greeks knew that a magnet attracts iron, and rubbed amber attracts light objects, such as straws, etc. However, the distinction 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 the Great Magnet - the Earth." This book, in fact, begins a truly scientific study of electrical and magnetic phenomena. Hilbert described in his book all the properties of magnets that were known in his era, and also set out the results of his own very important experiments. He pointed out a number of significant differences between electric and magnetic attractions and introduced the word "electricity".

Although after Hilbert the difference between electrical and magnetic phenomena was already indisputably clear to everyone, nevertheless a number of facts indicated that, with all their differences, these phenomena are somehow closely and inextricably linked with each other. The most striking facts were the magnetization of iron objects and the magnetization reversal of magnetic arrows under the influence of lightning. In his work Thunder and Lightning, the French physicist Dominique François Arago (1786-1853) describes, for example, such a case. “In July 1681, the ship“ Queen ”, located a hundred miles from the coast, in the open sea, was struck by lightning, which caused significant damage to the masts, sails, etc. When night fell, the position of the stars revealed that from the three compasses 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 when lightning striking a house strongly magnetized steel knives, forks and other objects in it.

At the beginning of the 18th century, it was already established that lightning is, in fact, a strong electric current flowing through the air; therefore, facts like those described above could suggest the idea that any electric current has some kind of magnetic properties. However, these properties of the current were discovered experimentally, and they were studied 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, ie, in the north-south direction, a magnetic needle 2 is suspended on a thin thread (Fig. 199, a). The arrow is known to also be set 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 through wire 1, we will see that the magnetic needle turns, trying to establish itself 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 a current, there are forces that cause the movement of the magnetic needle, that is, forces similar to those that act near natural and artificial magnets. We will call such forces magnetic forces, just as we call the 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 designate that special state of space, which manifests itself in actions, electrical forces. In the same way, we will call a magnetic field the state of space that 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, that is, a magnetic field is created.

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

We used platinum, gold, silver, brass and iron wires with the same result, as well as tin and lead polices and mercury. "

Oersted conducted all his experiments with metals, that is, with conductors, in which conductivity, as we now know, has an electronic character. However, it is not difficult to carry out Oersted's experiment by replacing the metal wire with a tube with an electrolyte or a tube in which a gas discharge occurs. We have already described such experiments in § 40 (Fig. 73) and saw 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 a 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 rotates, tending to become perpendicular to the direction of the current.

Thus, we can assert: a magnetic field arises around any current. 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 an electric current, the most characteristic is the creation of a magnetic field. Chemical actions of current in some conductors - electrolytes - take place, in others - metals - are absent. The heat generated by the current can be more or less at the same current, depending on the resistance of the conductor. In superconductors, it is even possible for a current to pass without the release of heat (§ 49). But the magnetic field is an inseparable companion of any electric current. It does not depend on any special properties of this or that conductor and is determined only by the strength and direction of the current. Most of the technical uses of electricity are also associated with the presence of a magnetic current field.

We examined in detail the properties of the electrostatic field generated by stationary electric charges. When electric charges move, a whole series of new physical phenomena arise, which we are starting to study.

It is now widely known that electric charges have a discrete structure, that is, elementary particles - electrons, protons, etc. are charge carriers. However, in most practically significant cases, this discreteness of charges does not manifest itself, therefore, the model of a continuous electrically charged medium describes well the phenomena associated with the movement of charged particles, that is, with an electric current.

Electric current is the directional movement of charged particles..

You are very familiar with the use of electric current, since electric current is extremely widely used in our life. It is no secret that our present civilization is mainly based on the production and use of electrical energy. It is enough to simply produce electrical energy, transfer it over long distances, and convert it into other required forms.

Let us briefly dwell on the possible manifestations of the action of an electric current.

Thermal action electric current manifests itself in almost all cases of current flow. Due to the presence of electrical resistance, when current flows, heat is released, the amount of which is determined by the Joule-Lenz law, with which you should be familiar. In some cases, the released heat is useful (in a variety of electric heating devices), often the release of heat leads to useless energy losses during the transmission of electricity.

Magnetic action current manifests itself in the creation of a magnetic field, leading to the appearance of interaction between electric currents and moving charged particles.

Mechanical action current is used in a variety of electric motors that convert electric current energy into mechanical energy.

Chemical action manifests itself in the fact that the flowing electric current can initiate various chemical reactions. So, for example, the process of production of aluminum and a number of other metals is based on the phenomenon of electrolysis - the reaction of decomposition of molten metal oxides under the action of an electric current.

Light action electric current manifests itself in the appearance of light radiation when an electric current passes. In some cases, the glow is a consequence of thermal heating (for example, in incandescent bulbs), in others, moving charged particles directly cause the appearance of light radiation.

In the very name of the phenomenon (electric current), echoes of old physical views are heard, when all electrical properties were attributed to a hypothetical electric fluid that fills all bodies. Therefore, when describing the motion of charged particles, a terminology similar to that used when describing the motion of ordinary liquids is used. This analogy extends beyond a simple coincidence of terms, many laws of motion of "electric fluid are analogous to the laws of motion of ordinary liquids, and the laws of direct electric current through wires, which are partially familiar to you, are similar to the laws of motion of liquid through pipes. Therefore, we strongly recommend that you repeat the section in which these phenomena are described - hydrodynamics.

1. What is the manifestation of the magnetic effect of an 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 you determine the poles of a magnet using a compass? 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 not randomly located around the conductor, but along a concentric circle.

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

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

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

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

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

• Using a magnetic needle that responds to the current in the wire.
• Using a sensitive voltmeter, connect it to the ends of the wire.