Application of the magnetic action of electric current. Actions of electric current: thermal, chemical, magnetic, light and mechanical

The presence of current in an electrical circuit is always manifested by some action. For example, working under a specific load or some related phenomenon. Consequently, it is the action of 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 effects. For example, these include thermal, chemical, magnetic, mechanical or light. In this case, various effects of 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 a conductor increases when current passes through it. Such conductors are various metals or their melts, semimetals or semiconductors, as well as electrolytes and plasma. For example, when an electric current is passed through a nichrome wire, it becomes very hot. This phenomenon is used in heating devices, namely: in electric kettles, boilers, heaters, etc. Electric arc welding has the highest temperature, namely, the heating of the electric arc can reach up to 7,000 degrees Celsius. At this temperature, easy melting of the metal is achieved.

The amount of heat generated directly depends on what voltage was applied to a given section, as well as on the electric current and the time it passes through the circuit.

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

chemical phenomenon

The chemical effect of electric current is the electrolysis of ions in the electrolyte. During electrolysis, the anode attaches anions to itself, and 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 acidic, alkaline or saline solution. Then a current is passed through the electrical circuit, which provokes the creation of a positive charge on one of the electrodes, and a negative charge on the other. The ions that are in solution are deposited on the electrode with a different charge.

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

Magnetic phenomenon

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

Thus, if you bring a magnetic compass needle closer to a conductor in which an electric current flows, it will begin to rotate and take a perpendicular position to the conductor. If you wind this conductor around an iron core and pass a direct current 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's explain: moving charges (charged particles) form a magnetic field. In this case, currents of opposite directions 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 light action is an incandescent lamp. In this light source, the spiral reaches the desired temperature value through the 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 remaining lion's share is converted into heat.

More modern analogues, for example, fluorescent lamps, most efficiently convert electricity into light. That is, about twenty percent of all energy lies at the basis of light. The phosphor receives UV radiation coming from a discharge that occurs in mercury vapor or inert gases.

The most effective implementation of the light action of 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 (different lengths and ranges). The efficiency of the LED reaches 50 percent.

Mechanical phenomenon

Recall that a magnetic field arises around a conductor carrying electric current. All magnetic actions are converted into movement. Examples include electric motors, magnetic lifting units, relays, etc.

In 1820, Andre Marie Ampère derived the well-known “Ampere’s Law,” which describes the mechanical effect of one electric current on another.

This law states that parallel conductors carrying electric current in the same direction experience attraction to each other, and those in the opposite direction, on the contrary, experience repulsion.

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

Actions of electric current

There are six effects of electric current:

1. Thermal effect of current (heating of heating devices);
2. Chemical effect of current (electric current in electrolyte solutions);
3. Magnetic effect of current.
4. Light effect of current.
5. Physiological effect of current.
6. Mechanical action of current.

Thermal effect of current

Chemical effect of current

Magnetic effect of current

Electric current creates a magnetic field, which can be detected by its effect on a permanent magnet. For example, if you bring a compass to a conductor through which electric current flows, the compass needle, which is a permanent magnet, will begin to move. If initially the compass needle was located along the lines of force of the earth's magnetic field, then after approaching a conductor with electric current, the needle will be oriented along the lines of force of the magnetic field of the conductor.

A coil consisting of a wound wire and a core attracts metal particles. Since both the coil and the core are made of different conductors, electrons are transferred to different conductors.

Wikimedia Foundation. 2010.

See what “Actions of electric current” are in other dictionaries:

Limit switching capacity of cyclic action of an electric relay- 117. Limiting switching capacity of the cyclic action of an electric relay D. Schaltvermögen bei Schaltspielen E. Limiting cyclic capacity F. Pouvoir limite de manoeuvre The highest current value that the output circuit of an electric ... ...

GOST 19350-74: Electrical equipment of electric rolling stock. Terms and definitions- Terminology GOST 19350 74: Electrical equipment of electric rolling stock. Terms and definitions original document: 48. Active static pressing of the pantograph Pressing the pantograph onto the contact wire while slowly increasing it... ... Dictionary-reference book of terms of normative and technical documentation

- (abbr. HIT) a source of EMF in which the energy of the chemical reactions occurring in it is directly converted into electrical energy. Contents 1 History of creation 2 Operating principle ... Wikipedia

GOST R 52726-2007: AC disconnectors and grounding switches for voltages over 1 kV and drives for them. General technical conditions- Terminology GOST R 52726 2007: AC disconnectors and grounding switches for voltages above 1 kV and drives for them. General technical conditions original document: 3.1 IP code: A coding system characterizing the degrees of protection provided by... ... Dictionary-reference book of terms of normative and technical documentation

This page needs significant revision. It may need to be Wikified, expanded, or rewritten. Explanation of reasons and discussion on the Wikipedia page: For improvement / October 23, 2012. Date of setting for improvement October 23, 2012 ... Wikipedia

Devices that convert various types of energy into electricity. Based on the type of energy converted, energy sources can be divided into chemical and physical. Information about the first chemical electrochemical cells (galvanic cells and batteries) ... ... Great Soviet Encyclopedia

P. d. is a self-propagating wave of changes in membrane potential, which is sequentially carried out to the axon of the neuron, transferring information. from the cell body of the neuron to the very end of its axon. During normal transmission of information. in the nerve networks P... Psychological Encyclopedia

CURRENT CARRIER MOBILITY- a quantity characterizing the electrical properties (see) and semiconductors (see), equal to the ratio of the average steady-state speed of movement of current carriers (electrons, ions, holes) in the direction of the electric field to the intensity E... ... Big Polytechnic Encyclopedia

The invention of aerothermal power plants is associated with observations of thermal air currents rising in the atmosphere. It is ideal to see them laminar, but this is a difficult task, they will always be subject to turbulence, and ... ... Wikipedia

delayed detonator- Detonates at a fixed time after electric current is passed through it. Used when preparing a directional explosion directional charge Topics... ... Technical Translator's Guide

Books

• Electrical safety, Kisarimov R.A.. 336 pp. The book provides an overview of the dangers of electric shock in everyday life and at work, and examines the effect of electric current on a person depending on the magnitude of the current.…

About the causes and nature of magnetic field lines (MFLs) that arise near permanent magnets and current-carrying conductors. In a previous article, I hypothesized that the magnetic field near a permanent magnet or current-carrying conductor represents an interference pattern from MSLs of varying intensity. I attach a certain physical meaning to the term MSL. These are not just geometric lines, but part of the complex structure of the magnetic field, which in turn consists of microscopic waves that have magnetic properties. When a piece of iron or iron filings is exposed to the magnetic field of a permanent magnet, this field is external (EMF) in relation to the piece of iron or iron filings. The VMF first induces its own magnetic field (SMF) in a piece of iron or in iron filings, and then interacts with this SMF through their MFL.

This also applies to conductors carrying current. As long as there is current in the conductors of a closed circuit (which means there is an SMP around the conductors), the VMF interacts with the SMP of the conductors through their MSL. When there is no current in the conductor, and therefore no MSL around the conductor, the EMF does not act on the conductor itself, although its MSL penetrate the microstructure of the conductor.

In this article we will talk about the interaction of magnets and conductors with current through MSL.

Let us recall what is known about this from scientific publications. As mentioned earlier, G. Oersted in 1820 experimentally demonstrated the interaction of a magnet and a conductor with current. The behavior of a magnetic needle near a conductor with direct current indicated that there was a magnetic field around this conductor. Subsequently, a close connection between the magnetic field and current was established. Summarizing his experiments, Oersted showed that the presence of current in the conductors of a closed circuit, whatever their nature, always entails the formation of an MSL magnetic field around the conductors of this circuit. It is the interaction of the MSL of the conductor with the MSL of the magnetic needle that causes it to turn one of its poles towards the conductor with current.

In 1821, the French scientist A. Ampere established the relationship between electricity and magnetism in the case of electric current passing through a circuit and the absence of such a relationship in static electricity.

To check whether the indicated MSL interaction is mutual, i.e. whether a magnet acts on a current-carrying conductor, the following experiment was carried out (Fig. 1). A conductor with direct current was suspended above a stationary permanent magnet. It turned out that a current-carrying conductor behaves similarly to a magnetic needle.

An interesting experiment is with a flexible conductor, which is located in close proximity to a parallel strip magnet. When a current appeared in the conductor, it wrapped around a strip magnet (Fig. 2). This indicated that MSLs appeared around each section of the current-carrying conductor, which interacted with the MSL of the strip magnet.

The same conclusion was made by D. Arago, who in his experiment drew attention to the fact that if you immerse an insulated wire carrying current in metal filings, the filings stick to it along its entire length, like a magnet. When the current is turned off, the sawdust disappears.

Similar interactions were established between two conductors with direct current located close to each other. In the experiment (Fig. 3), two parallel conductors are installed at a short distance from each other. These conductors were attracted or repelled depending on its direction. In these and other experiments it was shown that the magnetic effect of an electric current is similar to the interaction of two magnets.

The experiments we have considered on the interaction of magnetic fields show that all interactions, both in the case of permanent magnets and between permanent magnets and current-carrying conductors, as well as two current-carrying conductors with each other, are reduced to the interaction of magnetic fields through their MSL. Taking into account the fact that in practice a large number of technical devices are created on the basis of the interaction of magnetic fields, in particular, on the basis of the interaction of magnetic fields and conductors with current, we should present some experiments that we will need later to explain some phenomena in this area.

Consider the following experiment on the interaction of a magnetic field and a conductor with current. In the magnetic field of a horseshoe magnet there is a straight section of a conductor carrying current. (Fig. 4). By changing the direction of the current in a conductor and changing its location relative to the direction of the magnetic field, you can determine the direction of the force acting on the conductor. When the current is turned on (depending on its direction), the conductor can be pulled into the magnet or pushed out of the magnet. In this case, the magnetic field acts on a current-carrying conductor only when it is located perpendicular to the direction of the MSL field. When the conductor and MSL are parallel, the interaction field does not occur.

The force acting on a current-carrying conductor in a magnetic field is determined from the relationship:

F= k*H*I*L*sina,

where H is the magnetic field strength, I is the current strength, L is the length of the straight section of the conductor, and a is the angle between H and I.

This relationship is called Ampere's law. In practice, in most cases one has to deal with conductors of various shapes through which current flows, and the effect of a magnetic field on such conductors with current is quite complex. Let's see how a magnetic field acts on simple forms of current-carrying conductors in the form of a coil or solenoid.

A coil with current, as experiments have shown, is similar to a flat magnet, the poles of which (north and south) are located on opposite planes of the coil. The poles are perpendicular to the planes of the current-carrying coil. You can determine which of these poles is north and which is south using the gimlet rule. The north pole of the coil with current is determined by the direction of its rotation handle - an analogy to the direction of the MSL. If you screw the gimlet in the direction of the current, then the MSLs emerging from the plane of the coil will point to the north pole. The magnetic poles of the solenoid are determined in the same way.

An external magnetic field, acting on a coil with current, tends to rotate it so that the MSL of the coil is parallel to the MSL of the external magnetic field. To analyze the forces acting on a current-carrying coil, it is convenient to make it rectangular in shape. In this case, assume that two sides of the coil are parallel to the direction of the magnetic field, and the other two are perpendicular (Fig. 5). The first two sides of the coil are not affected by the magnetic field, but the other two sides of the coil are subject to equal and opposite magnetic forces created by the opposite direction of the current. These forces form a torque that turns the coil with the current plane perpendicular to the direction of the magnetic field. On the other two sides of the coil, the magnetic field acts on two equal but oppositely directed forces, which tend to deform (compress or stretch) the coil depending on the direction of the current.

Based on the results of the above and other experiments, the following conclusions can be drawn.

The magnetic field acts on a straight section of a current-carrying conductor with a force, the direction of which is perpendicular to the direction of the current and the direction of the MSL of the magnetic field;

The magnetic field creates a torque that tends to rotate the coil or solenoid so that the direction from the south pole of the coil or solenoid to the north pole coincides with the direction of the field;

The magnetic field does not act on current-carrying conductors located along the MSL direction;

MSLs are not just geometric lines, but part of the complex structure of a magnetic field, which in turn consists of microscopic waves that have magnetic properties.

We will talk about the nature and characteristics of these and other forces in the next article.

“Since I have long considered the forces manifested in electrical phenomena as universal natural forces, I had to deduce from this magnetic actions. I therefore hypothesized that electric forces, when in a strongly bound state, must have some effect on the magnet.

I could not then carry out an experiment to test it, since I was traveling and my attention was entirely occupied with the development of the chemical system 4 .

Hans Christian Oersted

Oersted's discovery, made in 1819 and published in 1820, was as follows. Oersted discovered that if a straight conductor is placed near a magnetic needle, the direction of which coincides with the direction of the magnetic meridian, and an electric current is passed through it, then the magnetic needle is deflected. Oersted did not determine the magnitude of the moment of force acting on a magnetic needle under the influence of an electric current. He only noted that the angle at which the needle deviates under the influence of current depends on the distance between it and the current, as well as, in modern language, on the strength of the current (in Oersted’s time the concept of current strength had not yet been firmly established).

Oersted's theoretical considerations regarding his discovery were not sufficiently clear. He said that at surrounding points in space an “electrical conflict” arises, which has a vortex character around the conductor. The article in which this discovery was first reported is called "Experiments Concerning the Effect of Electric Conflict on the Magnetic Needle" by Ørsted.

Andre Marie Ampere

Oersted's discovery aroused great interest and served as an impetus for new research. Also in 1820, new results were obtained. Thus, Arago showed that a current-carrying conductor acts on iron objects, which become magnetized. French physicists Biot and Savard established the law of action of a straight conductor carrying current on a magnetic needle. By placing a magnetic needle near a straight conductor carrying current and observing the change in the period of oscillation of this needle depending on the distance to the conductor, they established that the force acting on the magnetic pole from the side of a straight conductor carrying current is directed perpendicular to the conductor and the straight line connecting the conductor to the pole, and its magnitude is inversely proportional to this distance. This result was analyzed, and after the introduction of the concept of the current element, a law was established known as the Biot-Savart law.

Also in 1820, a new important result in the field of electromagnetism was obtained by the Frenchman Andre Marie Ampère (1775-1836). By this time, Ampere was already a famous scientist; he had a number of works on mathematics, physics and chemistry. In addition, Ampere was attracted to biology and geology. He was keenly interested in philosophy and at the end of his life he wrote a large work, “A Study in the Philosophical Sciences,” devoted to the issue of classification of sciences. Ampere's worldview was formed to a large extent under the influence of French educators and materialists. His views on physical phenomena differed from those of most of his contemporaries. He was opposed to the concept of "weightless". “Is it really necessary,” said Ampere, “to invent a special fluid for each new group of phenomena?” Ampère very quickly accepted the wave theory of light, which, according to Arago, along with Ampère’s own theory, which explained magnetic phenomena by electric ones, “became his favorite theory” 5 . Ampere was an opponent of the caloric theory and believed that the essence of heat lies in the movement of atoms and molecules. He even wrote a paper on the wave theory of light and the theory of heat. At the beginning of September 1820, Arago informed French academics about Oersted's discovery and soon demonstrated his experiments at a meeting of the Paris Academy of Sciences. Ampere became extremely interested in this discovery. First of all, it prompted him to think about the possibility of reducing magnetic phenomena to electrical ones and eliminating the idea of ​​a special magnetic fluid. Soon Ampere was already reporting on his new hypotheses and talking about experiments that should confirm them. In a brief summary of his first report, Ampère wrote:

“I reduced the phenomena observed by Mr. Oersted to two general facts; I showed that the current existing in a voltaic column acts on a magnetic needle in the same way as the current of a connecting wire. I have described experiments by which I established the attraction or repulsion of the entire magnetic needle under the action of the connecting wire. I described the devices that I intended to build and, among other things, galvanic screws and spirals. I pointed out that the latter will produce in all cases the same actions as magnets. I then touched upon some details concerning my view of magnets, according to which they owe their properties solely to electric currents located in planes perpendicular to their axis. I also touched upon some details regarding similar currents that I assumed in the globe. Thus, I reduced all magnetic phenomena to purely electrical actions." 6 .

At the end of 1820 - beginning of 1821, he made more than ten reports. In them, Ampère reported both his experimental research and theoretical considerations. Ampere demonstrated experimentally the interaction of two straight conductors with current, the interaction of two closed currents, etc. He also demonstrated the interaction of a solenoid and a magnet; equivalent behavior of a solenoid and a magnetic needle in the field of terrestrial magnetism and a number of other experiments.

Ampere's theoretical conclusions were a development of the ideas he expressed in his first message: they have now been confirmed by experimental research. He explained the properties of a magnet by the presence of currents in it, and the interaction of magnets by the interaction of these currents. At first Ampere considered these currents to be macroscopic; a little later he came to the hypothesis of molecular currents. Ampere also develops a corresponding point of view on the issue of terrestrial magnetism, believing that currents flow inside the Earth that determine its magnetic field.

Ampere's theoretical considerations met with objections from some physicists. Not everyone could immediately reject the existence of “magnetic fluid.” In addition, Ayper's views did not seem to fit into the general understanding of physical phenomena; in particular, they assumed the presence of forces that depended not only on distance, but also on movement (on the strength of the current). Finally, they could seem to be a modification of Cartesian ideas. Indeed, Ampere spoke in a Cartesian spirit about the forces acting between electric currents. He wrote that he “sought to explain it (force - B.S.) by the reaction of a liquid diffused in space, the vibration of which causes a light phenomenon” 7

However, such reasoning is not typical for Ampere, and his main work is called “The Theory of Electrodynamic Phenomena, Deduced Exclusively from Experience.”

A particularly active opponent of Ampere's theory was Biot, who proposed a different explanation for the interaction of electric currents. He believed that when an electric current flows through a conductor, then under its action the chaotically located magnetic dipoles that are present in the conductor are oriented in a certain way. As a result of this, the conductor acquires magnetic properties and forces arise that act between the conductors through which electric current flows.

Ampere objected to this theory, based on Faraday's discovery of the so-called electromagnetic rotation. Faraday, using a special device (Fig. 51), established the fact of continuous rotation of a magnet around a current and a current around a magnet (1821). Amper wrote:

“As soon as the discovery of the first continuous rotational motion made by Faraday was published, I immediately saw that it completely refutes this hypothesis, and these are the terms in which I expressed my thought ... A movement that continues constantly in one direction, despite friction, despite the resistance of the medium, and, moreover, the movement caused by the interaction of two bodies remaining all the time in the same state is an unprecedented fact among everything that we know about the properties of inorganic matter. He proves that the action proceeding from galvanic conductors cannot be caused by the special distribution of certain liquids present in these conductors in a state of rest, to which ordinary electrical attractions and repulsions owe their origin. This action can only be attributed to fluids that move in the conductor, quickly being transferred from one end to the other." 8 .

Indeed, with no constant arrangement of force centers (such as Biot’s magnetic dipoles), it is possible to achieve their continuous movement so that they always return to their original position. Otherwise, the principle of the impossibility of a perpetual motion machine would be refuted.

Having discovered the interaction of currents, the equivalence of a magnet and a solenoid, etc., as well as putting forward a number of hypotheses, Ampere set himself the task of establishing the quantitative laws of this interaction. To solve it, it was natural to proceed in a similar manner to what was done in the theory of gravitation or electrostatics, namely, to imagine the interaction of finite conductors with current as a result of the total interaction of infinitesimal elements of conductors through which electric current flows, and thus reduce this problem to finding the differential law , which determines the strength of interaction between elements of conductors carrying current or between elements of currents.

However, this task is more difficult than the corresponding task in the theory of gravitation or electrostatics, since the concepts of a material point or point charge have a direct physical meaning and experiments could be carried out with them, while the element of electric current had no such meaning and could not be realized at that time. time was impossible. Ampere proceeds as follows. Based on known experimental data, he puts forward the hypothesis that the force of interaction between the elements of current-carrying conductors is as follows:

where i 1 and i 2 are the current strength, ds 1 and ds 2 are the elements of the conductors, r is the distance between the elements, n is some (yet unknown) number, Φ (ε, θ 1, &theta 2 ;) is a yet unknown function angles that determine the relative position of the conductor elements (Fig. 52).

These assumptions are of different nature. Thus, the assumption about the dependence of dF on current follows directly from experiments. The assumption that the force dF should be proportional to ds 1 and ds 2, as well as to some as yet unknown function of the angles, can also be considered as a consequence obtained from experiments, although not directly. The assumption about the dependence of dF on the distance between the elements of the shackles is based, of course, only on the supposed analogy with the forces of gravity or the forces of interaction between electric charges.

It is possible to determine n and the expression of the angle function Φ (ε, θ 1, &theta 2 ;) by measuring the interaction forces between conductors with current, differently located relative to each other, of different sizes and shapes. However, in Ampere's time this was very difficult to do, since the currents in question were small. Ampere got out of the situation by studying the cases of equilibrium of conductors with currents of different locations and different shapes. As a result, he determined n and Φ (ε, θ 1, &theta 2 ;) and obtained the final result for the law of interaction of current elements:

In vector form and corresponding units, this law has the form

where dFi3 is the force acting on the second current element.

Thus, the law established by Ampere differs from the law of interaction of two elements of currents, which is currently called Ampere’s law and is expressed by the formula

The mistake made by Ampere did not affect the results of the calculations, since the law was naturally applied to simple cases of determining the interaction of closed conductors with direct currents. In this case, both formulas lead to the same result, since they differ from each other by an amount that, when integrated over a closed loop, gives zero.

In 1826, Ampere's main work, “The Theory of Electrodynamic Phenomena Derived Exclusively from Experience,” was published. In this book, Ampere systematically presented his research on electrodynamics and, in particular, presented the derivation of the law of interaction of current elements. In conclusion of the review of Ampere’s works, it should be noted that he used the concept and * the term “current strength”, as well as the concept of “voltage”, although he did not provide a clear and precise formulation of these concepts. Ampere also came up with the idea of ​​​​creating a device for measuring current strength (ammeter). Finally, it should be pointed out that Ampere proposed the idea of ​​​​an electromagnetic telegraph, which was then put into practice.

An important achievement of electrodynamics in the first half of the 19th century. was the establishment of the laws of the direct current circuit. Already at the beginning of the 19th century. it has been suggested that the strength of the current (the effect of current) in a circuit depends on the properties of the conductors. Thus, the larger the cross-section of the conductors, the larger the Petrov element. Somewhat later, the dependence of the chemical effect of current on conductors was established by Davy, who showed that this effect is greater, the shorter the conductors and the larger their cross-section.

Georg Ohm

In the mid-20s, the German physicist Georg Ohm (1787-1854) began researching direct current circuits. First of all, Ohm experimentally established that the magnitude of the electric current depends on the length of the conductors, their cross-section and the number of galvanic elements included in the circuit. To measure the current, Ohm used a simple galvanometer, which was a torsion balance with a magnetic needle suspended from a thread; A conductor connected to the electric current circuit was placed under the arrow. When electric current flowed through the conductor, the magnetic needle was deflected. By turning the head of the torsion balance, bringing the pointer to its original position, Ohm measured the moment of forces acting on the small pointer. Like Ampere, he believed that the magnitude of this moment is proportional to the strength of the current.

Rice. 53. Ohm's device (Ohm's drawings)

First, Ohm investigated the dependence of the current on the length of the conductor connected to the circuit. As a current source, he used a thermoelement consisting of bismuth and copper (Fig. 53). A bismuth rod bb", shaped like the letter P, is connected to copper strips. Ohm found that the “power of the magnetic action” of the current (current strength) of the conductor under study is determined by the formula

X=a/(b+x),

where x is the length of the conductor, a and b are constants, and a depends on the exciting force of the thermoelement (erregende Kraft), and b - on the characteristics of the rest of the circuit, including the thermoelement.

Ohm then established that if not one, but m identical current sources are connected to the circuit, then “the strength of the magnetic action of the current”

X=ma/(mb+x).

Ohm also determined how the current strength X in a conductor depends on its length and cross-section. He found that

X = kw a/l,

where k is the conductivity coefficient of the conductor (Leitungsvermogen), w is the cross-section, and l is the length of the conductor, and is the electrical voltage at its ends (Electrische Spannung).

Ohm investigated the distribution of electric potential "electroscopic force" along a homogeneous conductor carrying current. To do this, he used an electrometer, which he connected to various points of the conductor when one of the points of the conductor was grounded. Finally, Ohm tried to theoretically comprehend the patterns he discovered. He proceeded from the idea of ​​electric current as the flow of electricity along a conductor. He drew an analogy between electric current and heat flow. He believed that, like a flow of heat, electricity flows through a conductor from one layer or element to another nearby one. The heat flow is determined by the temperature difference in the nearby layers of the rod through which this heat flows (i.e., the temperature gradient). Similarly, Ohm believes that the flow of electricity should be determined by the difference in electrical force in nearby sections of the conductor. He wrote:

“I believe that the magnitude of the transfer (of electricity. - B.S.) between two nearby elements, under other equal circumstances, is proportional to the difference in electric force in these elements, just as in the study of heat it is accepted that the thermal transfer between two elements of heat is proportional their temperature differences" 9 .

By electric force here, Ohm does not mean the intensity of the electric field, but the value that is shown by an electroscope connected to any point of the conductor if one of the points of the galvanic circuit is grounded, i.e., potential difference. Ohm also called this quantity “electroscopic force.”

As often happens, an analogy extended too far leads to errors. Thus, Ohm, from the fact that temperature is proportional to the amount of heat, erroneously concluded that the “electroscopic force” in a conductor is proportional to the amount of electricity at each point. Solving the problem of the propagation of potential along a current circuit, Ohm believed that he thereby found the amount of electricity in the corresponding places of the conductor.

The law discovered by Ohm and bearing his name did not immediately receive recognition. Back in the 30s, doubts were expressed about it and the limitations of its use were noted. However, in a number of works by various physicists who used more advanced measurement methods, Ohm's conclusions were confirmed and his law received universal recognition. In doing so, Ohm's misconceptions were also corrected.

Kirchhoff, in his works dating back to 1845-1848, clarified the concept of “electroscopic force”. He established the identity of the concept of this quantity and the concept of potential in electrostatics. Kirchhoff also established well-known rules for electrical circuits.

More than 15 years after the discovery of Ohm's law, a law was established that determines the amount of heat generated by an electric current in a circuit; it was established experimentally by the Englishman Joule (1843) and independently by the St. Petersburg academician E. H. Lenz (1844). Currently it is called the Joule-Lenz law.

1 See: Jones W. The Life and Letters of Faraday. Vol. II. London, 1870 p. 395.
2 Oersted H. Ch. Der Geist und der Natur B. 2, MCnchen, 1851, S. 435.
3 Winterl I. Darstellung der vier Bestandtheil der anorganischen Natur. Verna, 1804.
4 Oersted H. Ch. J. Chem. Phys., B. 32, 1821, s. 200-201.
5 Arago F. Biographies of famous astronomers, physicists and geometers. T. II. St. Petersburg, I860, p. 304.
6 Ampere A. M. Electrodynamics. M., Publishing House of the USSR Academy of Sciences, 1954, p. 410-411.
7 Ampere A. M. Electrodynamics, p. 124.
8 Ampere A. M. Electrodynamics, p. 127-128.
9 Ohm G. Gesammelte Adhandlungen. Leipzig, 1892, S. 63.

The possible existence of a close connection between electricity and magnetism was suggested by the very first researchers, struck by the analogy of the electrostatic and magnetostatic phenomena of attraction and repulsion. This idea was so widespread that first Cardan, and then Hilbert, considered it a prejudice and tried in every possible way to show the difference between these two phenomena. But this assumption arose again in the 18th century, with greater justification, when the magnetizing effect of lightning was established, and Franklin and Beccaria managed to achieve magnetization using the discharge of a Leyden jar. Coulomb's laws, formally the same for electrostatic and magnetostatic phenomena, again raised this problem.

After Volta's battery made it possible to produce electric current for a long time, attempts to discover the connection between electrical and magnetic phenomena became more frequent and more intense. And yet, despite intensive searches, the discovery had to wait for twenty years. The reasons for such a delay should be sought in the scientific ideas that prevailed at that time. All forces were understood only in the Newtonian sense, that is, as forces that act between material particles along a straight line connecting them. Researchers therefore endeavored to discover forces of this kind by constructing devices by which they hoped to detect the supposed attraction or repulsion between a magnetic pole and an electric current (or, more generally, between a "galvanic fluid" and a magnetic fluid), or by attempting to magnetize a steel needle, directing current through it.

Gian Domenico Romagnosi (1761-1835) also tried to discover the interaction between galvanic and magnetic fluid in the experiments he described in an article of 1802, which Guglielmo Libri (1803-1869), Pietro Configliacchi (1777-1844) and many others later referred to , attributing to Romagnosi the priority of this discovery. It is enough, however, to read this article to be convinced that in Romagnosi's experiments, carried out with an open-circuit battery and a magnetic needle, there was no electric current at all, and therefore the most that he could observe was ordinary electrostatic action.

When, on July 21, 1820, in one very laconic four-page article (in Latin), entitled “Experimenta circa effectum conflictus electrici in acum magneticam,” the Danish physicist Hans Christian Oersted (1777-1851) described a fundamental experiment in electromagnetism, proving that the current in a straight conductor running along the meridian deflects the magnetic needle from the direction of the meridian, the interest and surprise of scientists was great not only because the long-sought solution to the problem was obtained, but also because the new experience, as it immediately became clear , indicated a force of a non-Newtonian type.

In fact, from Oersted’s experiment it was clearly clear that the force acting between the magnetic pole and the current element is directed not along the straight line connecting them, but along the normal to this straight line, i.e., it is, as they said then, “a turning force.” " The significance of this fact was felt even then, although it was fully realized only many years later. Oersted's experience caused the first crack in Newton's model of the world.

The difficulty in which science has found itself can be judged, for example, by the confusion in which the Italian, French, English and German translators were when they translated Oersted's Latin article into their native language. Often, having made a literal translation that seemed unclear to them, they cited the Latin original in a note.

Indeed, what remains unclear in Oersted’s article even today is the explanation that he is trying to give to the phenomena he observed, which, in his opinion, were caused by two oppositely directed spiral movements around the conductor of “electrical matter, respectively positive and negative.”

The uniqueness of the phenomenon discovered by Ørsted immediately attracted much attention from experimentalists and theorists. Arago, returning from Geneva, where he was present at similar experiments repeated by De la Rive, spoke about them in Paris, and in September of the same 1820 he assembled his famous installation with a vertical current conductor passing through a horizontally located piece of cardboard sprinkled with iron sawdust. But he did not find the circles of iron filings that we usually notice when conducting this experiment. Experimenters have been seeing these circles clearly ever since Faraday put forward the theory of “magnetic curves” or “lines of force.” Indeed, often, in order to see something, you need to really desire it! Arago only saw that the conductor, as he put it, “is stuck with iron filings as if it were a magnet,” from which he concluded that “the current causes magnetism in iron that has not been subjected to prior magnetization.”

All in the same 1820, Biot read out two reports (October 30 and December 18), in which he reported on the results of an experimental study he and Savart conducted. Trying to discover the law that determines the dependence of the magnitude of the electromagnetic force on distance, Biot decided to use the oscillation method, which Coulomb had previously used. To do this, he assembled an installation consisting of a thick vertical conductor located next to a magnetic needle: when the current in the conductor is turned on, the needle begins to oscillate with a period depending on the electromagnetic force acting on the poles at different distances from the center of the needle to the current-carrying conductor. Having measured these distances, Biot and Savard derived the well-known law that now bears their name, which in its first formulation did not take into account the intensity of the current (they did not yet know how to measure it).

Having learned about the results of the experiments of Biot and Savart, Laplace noticed that the action of the current can be considered as the result of individual actions on the poles of the arrow of an infinite number of infinitesimal elements into which the current can be divided, and concluded from this that each element of the current acts on each pole with a force , inversely proportional to the square of the distance of this element from the pole. The fact that Laplace took part in the discussion of this problem is stated by Biot in his work “Precis elementaire de physique expo-rimentale”. In the writings of Laplace, as far as we know, there is no hint of such a remark, from which we can conclude that he apparently expressed this in an oral friendly conversation with Biot himself.

To supplement his knowledge of this elementary force, Biot tried, this time alone, to determine experimentally whether and, if so, how the action of a current element on a pole changes with a change in the angle formed by the direction of the current and the straight line connecting the middle of the element with the pole . The experiment consisted of comparing the effect that a current parallel to it and a current directed at an angle have on the same arrow. From the data of Biot's experiment, through a calculation that he did not publish, but which was certainly erroneous, as F. Savary (1797-1841) showed in 1823, he determined that this force is proportional to the sine of the angle formed by the direction of the current and the straight line , connecting the point in question with the middle of the current element. Thus, what is now called “Laplace’s first elementary law” is, to a large extent, Biot’s discovery.

Mario Liezzi "History of Physics"