What happens in a source of electric current. Electric current, sources of electric current: definition and essence. From the history of inventions

Preface.

What is electric current and what is necessary for its occurrence and existence for the time we need?

The word "current" means the movement or flow of something. Electric current is the ordered (directed) movement of charged particles. To obtain an electric current in a conductor, you need to create an electric field in it. In order for an electric current to exist in a conductor for a long time, it is necessary to maintain an electric field in it all this time. An electric field is created in conductors and can be maintained for a long time sources of electric current . Currently, humanity uses four main sources of current: static, chemical, mechanical and semiconductor (solar batteries), but in each of them work is done to separate positively and negatively charged particles. Separate particles accumulate at the poles of the current source, which is the name given to the places to which conductors are connected using terminals or clips. One pole of the current source is charged positively, the other - negatively. If the poles are connected by a conductor, then under the influence of the field, free charged particles in the conductor will move, and an electric current will arise.

Electricity.

Sources of electric current.

Until 1650, the time when great interest in electricity arose in Europe, there was no known way to easily obtain large electrical charges. With the growing number of scientists interested in electrical research, one could expect the creation of ever simpler and more efficient ways of generating electrical charges.

Otto von Guericke invented the first electric machine. He poured molten sulfur into a hollow glass ball, and then, when the sulfur hardened, he broke the glass, not realizing that the glass ball itself could serve his purposes just as well. Guericke then strengthened the sulfur ball as shown in Fig. 1 so that it could be rotated with a handle. To obtain a charge, it was necessary to rotate the ball with one hand, and with the other, press a piece of skin against it. Friction raised the ball's potential to a value sufficient to produce sparks several centimeters long.

This machine was painful

great assistance in experimental

nom studying electricity, but

even more difficult tasks of “keeping

supply" and "reserve" of electricity

ical charges were solved

only thanks to what follows

progress of physics. The fact is that powerful charges that

could be created on bodies using electrostatic

Guericke's cars quickly disappeared. At first it was thought that the reason for this was the “evaporation” of charges. To prevent

To “evaporate” charges, it was proposed to enclose charged bodies in closed vessels made of insulating material. Naturally, glass bottles were chosen as such vessels, and water was chosen as the electrified material, since it was easy to pour into bottles. To be able to charge the water without opening the bottle, a nail was passed through the cork. The idea was good, but for reasons unknown at the time, the device did not work so well. As a result of intensive experiments, it was soon discovered that the stored charge and thus the force of the electric shock could be dramatically increased if the bottle was coated inside and out with a conductive material, such as thin sheets of foil. Moreover, if you connect a nail using a good conductor to a layer of metal inside the bottle, it turns out that you can do without water at all. This new “storage” of electricity was invented in 1745 in the Dutch city of Leiden and was called the Leyden jar (Fig. 2).

The first who discovered a different possibility for generating electricity than through electrification by friction was the Italian scientist Luigi Galvani (1737-1798). He was a biologist by profession, but worked in a laboratory where experiments were carried out with electricity. Galvani discovered a phenomenon that was known to many before him; it consisted in the fact that if the leg nerve of a dead frog was excited by a spark from an electric machine, then the entire leg began to contract. But one day Galvani noticed that the paw began to move when only a steel scalpel came into contact with the nerve of the paw. The most surprising thing was that there was no contact between the electric machine and the scalpel. This amazing discovery forced Galvani to conduct a series of experiments to discover the cause of electric current. One of the experiments was carried out by Galvani to find out whether the same movements in the paw were caused by the electricity of lightning. To do this, Galvani hung several frog legs on brass hooks in a window covered with iron bars. And he found, contrary to his expectations, that contractions of the paws occur at any time, regardless of weather conditions. The presence of an electric machine or other source of electricity nearby turned out to be unnecessary. Galvani further established that instead of iron and brass, any two dissimilar metals could be used, and the combination of copper and zinc caused the phenomenon in the most distinct form. Glass, rubber, resin, stone and dry wood had no effect at all. Thus, the origin of the current still remained a mystery. Where does the current appear - only in the tissues of the frog's body, only in dissimilar metals, or in a combination of metals and tissues? Unfortunately, Galvani came to the conclusion that the current originates exclusively in the tissues of the frog's body. As a result, to his contemporaries the concept of “animal electricity” began to seem much more real than electricity of any other origin.

Another Italian scientist Alessandro Volta (1745-1827) finally proved that if you place frog legs in aqueous solutions of certain substances, then galvanic current does not arise in the tissues of the frog. In particular, this was the case for spring or generally clean water; this current appears when acids, salts or alkalis are added to water. Apparently, the greatest current occurred in a combination of copper and zinc placed in a dilute solution of sulfuric acid. The combination of two plates of dissimilar metals immersed in an aqueous solution of alkali, acid or salt is called a galvanic (or chemical) cell.

If only friction and chemical processes in galvanic cells were the means to obtain electromotive force, then the cost of electrical energy required to operate various machines would be extremely high. As a result of a huge number of experiments, scientists from different countries made discoveries that made it possible to create mechanical electrical machines that generate relatively cheap electricity.

At the beginning of the 19th century, Hans Christian Oersted made the discovery of a completely new electrical phenomenon, which consisted in the fact that when current passes through a conductor, a magnetic field is formed around it. A few years later, in 1831, Faraday made another discovery, equal in significance to Oersted's discovery. Faraday discovered that when a moving conductor crosses magnetic field lines, an electromotive force is induced in the conductor, causing a current in the circuit in which the conductor is included. The induced EMF changes in direct proportion to the speed of movement, the number of conductors, and the strength of the magnetic field. In other words, the induced emf is directly proportional to the number of lines of force crossed by the conductor per unit time. When a conductor crosses 100,000,000 lines of force in 1 second, the induced emf is equal to 1 Volt. By manually moving a single conductor or wire coil in a magnetic field, large currents cannot be obtained. A more efficient way is to wind the wire on a large spool or make the spool into a drum. The coil is then mounted on a shaft located between the poles of the magnet and rotated by the force of water or steam. This is, in essence, how an electric current generator works, which belongs to the mechanical sources of electric current and is actively used by humanity at the present time.
People have been using solar energy since ancient times. Back in 212 BC. e. With the help of concentrated solar rays, they lit the sacred fire near the temples. According to legend, around the same time, the Greek scientist Archimedes, while defending his hometown, set fire to the sails of the ships of the Roman fleet.

The Sun is a thermonuclear reactor located 149.6 million km away from the Earth, emitting energy that reaches the Earth mainly in the form of electromagnetic radiation. The largest part of the solar radiation energy is concentrated in the visible and infrared parts of the spectrum. Solar radiation is an inexhaustible renewable source of environmentally friendly energy. Without harming the ecological environment, 1.5% of all solar energy falling on the earth can be used, i.e. 1.62 *10 16 kilowatt hours per year, which is equivalent to a huge amount of standard fuel - 2 *10 12 tons.

The designers' efforts are moving along the path of using photocells to directly convert solar energy into electrical energy. Photoconverters, also called solar panels, consist of a number of photocells connected in series or parallel. If the converter must charge a battery that powers, for example, a radio device during cloudy times, then it is connected in parallel to the terminals of the solar battery (Fig. 3). Elements used in solar batteries must have high efficiency, favorable spectral characteristics, low cost, simple design and low weight. Unfortunately, only a few of the photocells known today meet at least partially these requirements. These are primarily some types of semiconductor photocells. The simplest of them is selenium. Unfortunately, the efficiency of the best selenium photocells is low (0.1...1%).

The basis of solar batteries are silicon photoconverters, which have the form of round or rectangular plates with a thickness of 0.7 - 1 mm and an area of ​​up to 5 - 8 sq.cm. Experience has shown that small elements with an area of ​​about 1 square meter give good results. see, having an efficiency of about 10%. Photocells made of semiconductor metals with a theoretical efficiency of 18% have also been created. By the way, the practical efficiency of photoelectric converters (about 10%) exceeds the efficiency of a steam locomotive (8%), the efficiency of solar energy in the plant world (1%), as well as the efficiency of many hydraulic and wind devices. Photovoltaic converters have virtually unlimited durability. For comparison, we can give the efficiency values ​​of various sources of electrical energy (in percent): combined heat and power plant - 20-30, thermoelectric converter - 6 - 8, selenium photocell - 0.1 - 1, solar battery - 6 - 11, fuel cell - 70, lead battery - 80 - 90.

In 1989, Boeing (USA) created a two-layer photocell consisting of two semiconductors - gallium arsenide and gallium antimonide - with a conversion factor of solar energy into electrical energy equal to 37%, which is quite comparable to the efficiency of modern thermal and nuclear power plants. It has recently been proven that the photovoltaic method of converting solar energy theoretically makes it possible to use solar energy with an efficiency of up to 93%! But initially it was believed that the maximum upper limit of the efficiency of solar cells was no more than 26%, i.e. significantly lower than the efficiency of high-temperature heat engines.

Solar batteries are currently used mainly in space, and on Earth only for power supply to autonomous consumers with a power of up to 1 kW, power supply for radio navigation

and low-power electronic equipment, drives for experimental electric vehicles and aircraft. As solar panels improve, they will find application in residential buildings for autonomous power supply, i.e. heating and hot water supply, as well as for generating electricity for lighting and powering household electrical appliances.

Sources of electric current Completed by: Anton Rubtsov, grade 8 B student of Municipal Educational Institution Secondary School No. 105 Scientific supervisor: E. A. Maslova, physics teacher

Choosing a topic I wanted to study the history of the creation of electric current sources, and also make some sources with my own hands, repeating the experiments of famous scientists. Relevance Humanity cannot exist without electrical energy, and perhaps someone will be able to discover new sources of electrical current that are more economical and less expensive. The purpose of the work is to study the main types of electric current sources, the principle of their operation and making the sources with your own hands. Objectives: 1. Consider the main types of sources of electric current. 2. Study the principle of operation of current sources. 3. Make some sources with your own hands.

Main part A current source is a device in which some type of energy is converted into electrical energy. In any current source, work is done to separate positively and negatively charged particles that accumulate at the poles of the source. Electric current is the directed (ordered) movement of charged particles (electrons, ions, etc.). The direction of movement of positively charged particles is taken as the direction of the current. If the current is created by negatively charged particles (for example, electrons), then the direction of the current is considered opposite to the direction of motion of the particles.

The history of the creation of the first current sources

Properties of amber Thales of Miletus was the first to pay attention to electric charge. He discovered that amber, rubbed with wool, acquires the properties of attracting small objects. Fossilized resin of ancient trees that grew on our planet 38-120 million years ago.

Electric machine Otto von Guericke Otto von Guericke invented the first electric machine. He poured molten sulfur inside a hollow glass ball, and then, when the sulfur hardened, he broke the glass. Guericke then strengthened the sulfur ball so that it could be rotated with a handle. To obtain a charge, it was necessary to rotate the ball with one hand, and with the other, press a piece of skin against it. The friction raised the tension of the ball to a value sufficient to produce sparks several centimeters long.

Leyden Jar A Leyden jar is a glass bottle wrapped in foil on both sides. There is a metal rod inside the jar. A jar connected by plates to an electric machine could accumulate a significant amount of electricity. If its plates were connected with a piece of thick wire, then a strong spark would jump at the point of the short circuit, and the accumulated electric charge would instantly disappear. This made it possible to obtain a short-term electric current. Then the jar had to be charged again. Now we call such devices electric capacitors.

Galvani's element Luigi Galvani (1737-1798) is one of the founders of the doctrine of electricity; his experiments with “animal” electricity laid the foundation for a new scientific direction - electrophysiology. As a result of experiments with frogs, Galvani suggested the existence of electricity within living organisms. A galvanic cell, a battery, was named after him.

Voltaic column Alesandro Volta (1745 - 1827) - Italian physicist, chemist and physiologist, inventor of a source of direct electric current. Its first source of current is a “voltaic column”. Volta alternately placed several dozen small zinc and silver circles on top of each other, placing paper moistened with salted water between them.

Main types of electric current sources Mechanical Thermal Light Chemical Thermal element Photocell Electrophore machine Galvanic cell

Animal current sources

Electricity inside living organisms Many plants experience damage currents. Sections of leaves and stems are always negatively charged relative to normal tissue.

Animals that produce electric current Electric stingray (up to 220 V) American catfish (up to 360 V) Eel (up to 1200 V)

Fruits and vegetables that produce electric current. Fruits and vegetables can be divided into those that initially contain and those that acquire intra-alkaline or acidic balance through the process of oxidation. The first include citrus fruits (lemon) and potatoes. And for the second, for example, pickled cucumber and pickled tomato.

Atmospheric electricity When air moves, various air currents become electrified as a result of contact. One part of the cloud (upper) is positively electrified, and the other (lower) is negatively electrified. At the moment when the charge of the cloud becomes large, a powerful electric spark—lightning—jumps between its two electrified parts.

Practical part

Homemade batteries To make homemade batteries, we will need instruments and materials: Copper plate Zinc plate Lemon, cucumber, soda, water, coins Voltmeter Connecting wires

Galvanic cell made from lemon Produces electric current with voltage

Galvanic cell from the first pickled cucumber Produces electric current with voltage

Galvanic cell from the second and third cucumbers

A battery of two pickled cucumbers produces an electric current with voltage

A battery of three pickled cucumbers produces an electric current with voltage

A light bulb connected to a chain of three pickled cucumbers. The chain has been assembled. The light bulb lights up.

Soda battery Produces electric current with voltage

Soda battery of two and three cells

A light bulb connected to a circuit of three soda elements. The circuit has been assembled. The light bulb lights up.

Salted battery Produces electric current with voltage

Conclusion To achieve the goal of this work, I solved the following problems: Considered the main types of sources of electric current. 1. Mechanical current sources 2. Thermal current sources 3. Light current sources 4. Chemical current sources Studied the principle of operation of current sources. I made some sources with my own hands. 1. Galvanic cell made of lemon. 2. Galvanic cell made from pickled cucumber. 3. Soda battery. 4. Salted battery.

Bibliography Abramov S.S.. Great Encyclopedia of Cyril and Mythodius. 2009 Wikipedia - the free encyclopedia. www. ru. wikipedia. org. Julian Holland. Large illustrated encyclopedia of the erudite. "Swallowtail" 2001; Kartsev V.P. Adventures of the Great Equations. M.: Education, 2007

From a physics course, everyone knows that electric current means the directed, ordered movement of particles carrying a charge. To obtain it, an electric field is formed in the conductor. The same is necessary for the electric current to continue to exist for a long time.

Sources of electric current can be:

• static;
• chemical;
• mechanical;
• semiconductor.

In each of them, work is performed where differently charged particles are separated, that is, an electric field of a current source is created. Having separated, they accumulate at the poles, at the places where the conductors are connected. When the poles are connected by a conductor, charged particles begin to move and an electric current is generated.

Sources of electric current: the invention of the electric machine

Until the mid-seventeenth century, generating electric current required a lot of effort. At the same time, the number of scientists working on this issue grew. And so Otto von Guericke invented the world's first electric machine. In one of the experiments with sulfur, it, molten inside a hollow glass ball, hardened and broke the glass. Guericke strengthened the ball so that it could be rotated. By rotating it and pressing a piece of leather, he received a spark. made it much easier to obtain short-term electricity. But more difficult problems were solved only with the further development of science.

The problem was that Guericke's charges quickly disappeared. To increase the duration of the charge, the bodies were placed in closed vessels (glass bottles), and the electrified material was water with a nail. The experiment was optimized when the bottle was coated on both sides with conductive material (sheets of foil, for example). As a result, they realized that they could do without water.

Frog legs as a current source

Another method of generating electricity was first discovered by Luigi Galvani. As a biologist, he worked in a laboratory where they experimented with electricity. He saw how a dead frog's leg contracted when it was excited by a spark from a machine. But one day the same effect was achieved by accident when a scientist touched it with a steel scalpel.

He began to look for the reasons where the electric current came from. The sources of electric current, according to his final conclusion, were located in the tissues of the frog.

Another Italian, Alessandro Volto, proved the inconsistency of the “frog” nature of the generation of current. It was observed that the highest current occurred when copper and zinc were added to the sulfuric acid solution. This combination is called a galvanic or chemical element.

But using such a means to obtain EMF would be too expensive. Therefore, scientists worked on another, mechanical, method of producing electrical energy.

How does a regular generator work?

At the beginning of the nineteenth century, G.H. Oersted discovered that when current passed through a conductor, a field of magnetic origin arose. And a little later, Faraday discovered that when the lines of force of this field intersect, an emf is induced into the conductor, which causes a current. The EMF changes depending on the speed of movement and the conductors themselves, as well as on the field strength. When crossing one hundred million lines of force per second, the induced EMF became equal to one Volt. It is clear that manual conduction in a magnetic field is not capable of producing a large electric current. Sources of electric current of this type have shown themselves to be much more effective when winding the wire on a large coil or producing it in the form of a drum. The coil was mounted on a shaft between a magnet and rotating water or steam. Such a mechanical current source is inherent in conventional generators.

Great Tesla

The brilliant Serbian scientist Nikola Tesla, devoting his life to electricity, made many discoveries that we still use today. Multiphase electric motors, energy transmission through multiphase alternating current - this is not the entire list of inventions of the great scientist.

Many are confident that the phenomenon in Siberia, called the Tunguska meteorite, was actually caused by Tesla. But perhaps one of the most mysterious inventions is a transformer capable of receiving voltages of up to fifteen million volts. What is unusual is both its structure and its calculations, which defy known laws. But in those days they began to develop vacuum technology, in which there were no ambiguities. Therefore, the scientist’s invention was forgotten for a while.

But today, with the advent of theoretical physics, there has been renewed interest in his work. Ether was recognized as a gas, which is subject to all the laws of gas mechanics. It was from there that the great Tesla drew his energy. It is worth noting that the etheric theory was very common in the past among many scientists. Only with the emergence of SRT - Einstein's special theory of relativity, in which he refuted the existence of the ether - was it forgotten, although the general theory formulated later did not challenge it as such.

But for now let us dwell in more detail on electric current and devices that are ubiquitous today.

Development of technical devices - current sources

Such devices are used to convert various types of energy into electrical energy. Despite the fact that physical and chemical methods for producing electrical energy were discovered a long time ago, they became widespread only in the second half of the twentieth century, when radio electronics began to develop rapidly. The original five galvanic pairs were supplemented by another 25 types. And theoretically, there can be several thousand galvanic pairs, since free energy can be realized on any oxidizing and reducing agent.

Physical current sources

Physical current sources began to develop a little later. Modern technology made increasingly stringent demands, and industrial thermal and thermionic generators successfully coped with increasing tasks. Physical current sources are devices where thermal, electromagnetic, mechanical and energy of radiation and nuclear decay are converted into electrical energy. In addition to the above, they also include electric machine and MHD generators, as well as those used to convert solar radiation and atomic decay.

To ensure that the electric current in the conductor does not disappear, an external source is needed to maintain the potential difference at the ends of the conductor. For this purpose, there are energy sources that have some potential difference to create and maintain. The emf of an electric current source is measured by the work performed by transferring a positive charge throughout a closed circuit.

The resistance inside a current source quantitatively characterizes it, determining the amount of energy lost when passing through the source.

Power and efficiency are equal to the ratio of the voltage in the external electrical circuit to the emf.

Chemical current sources

A chemical current source in an EMF electrical circuit is a device where the energy of chemical reactions is converted into electrical energy.

It is based on two electrodes: a negatively charged reducing agent and a positively charged oxidizing agent, which are in contact with the electrolyte. A potential difference, EMF, occurs between the electrodes.

Modern devices often use:

• as a reducing agent - lead, cadmium, zinc and others;
• oxidizer - nickel hydroxide, lead oxide, manganese and others;
• electrolyte - solutions of acids, alkalis or salts.

Dry elements made of zinc and manganese are widely used. A zinc vessel (having a negative electrode) is taken. A positive electrode with a mixture of manganese dioxide and carbon or graphite powder is placed inside, which reduces the resistance. The electrolyte is a paste of ammonia, starch and other components.

A lead acid battery is most often a secondary chemical source of current in an electrical circuit, which has high power, stable operation and low cost. Batteries of this type are used in a variety of fields. They are often preferred for starter batteries, which are especially valuable in automobiles, where they generally have a monopoly.

Another common battery consists of iron (anode), nickel oxide hydrate (cathode) and an electrolyte - an aqueous solution of potassium or sodium. The active material is placed in nickel-plated steel tubes.

The use of this species declined after the Edison plant fire in 1914. However, if we compare the characteristics of the first and second types of batteries, it turns out that the operation of iron-nickel batteries can be many times longer than lead-acid ones.

DC and AC generators

Generators are devices that are aimed at converting mechanical energy into electrical energy.

The simplest direct current generator can be imagined as a frame of conductor, which is placed between the magnetic poles, and the ends are connected to insulated half rings (collector). For the device to work, it is necessary to ensure rotation of the frame with the collector. Then an electric current will be induced in it, changing its direction under the influence of magnetic lines of force. It will go into the external circuit in a single direction. It turns out that the collector will rectify the alternating current generated by the frame. To achieve constant current, the collector is made of thirty-six or more plates, and the conductor consists of many frames in the form of an armature winding.

Let's consider what is the purpose of a current source in an electrical circuit. Let's find out what other current sources exist.

current, current strength, current source

An electrical circuit consists of a current source that, together with other objects, creates a path for the current. And the concepts of EMF, current and voltage reveal the electromagnetic processes occurring during this process.

The simplest electrical circuit consists of a current source (battery, galvanic cell, generator, etc.), energy consumers of electric motors, etc.), as well as wires connecting the terminals of the voltage source and the consumer.

An electrical circuit has internal (electricity source) and external (wires, switches and circuit breakers, measuring instruments) parts.

It will only work and have a positive value if a closed circuit is ensured. Any break causes the current to stop flowing.

An electrical circuit consists of a current source in the form of galvanic cells, electric batteries, electromechanical and photocells, and so on.

Electric motors that convert energy into mechanical energy, lighting and heating devices, electrolysis installations, and so on act as electrical receivers.

Auxiliary equipment includes devices used for switching on and off, measuring instruments and protective mechanisms.

All components are divided into:

• active (where the electrical circuit consists of an EMF current source, electric motors, batteries, and so on);
• passive (which includes electrical receivers and connecting wiring).

The circuit can also be:

• linear, where the resistance of the element is always characterized by a straight line;
• nonlinear, where resistance depends on voltage or current.

Here is the simplest diagram where a current source, a key, an electric lamp, and a rheostat are included in the circuit.

Despite the widespread widespread use of such technical devices, especially recently, people are increasingly asking questions about installing alternative energy sources.

Variety of electrical energy sources

What other sources of electric current exist? It's not just sun, wind, land and tides. They have already become the so-called official alternative sources of electricity.

It must be said that there are a lot of alternative sources. They are not common because they are not yet practical and convenient. But, who knows, maybe the future will be just theirs.

So, it is possible to obtain electrical energy from salt water. A power plant using this technology has already been created in Norway.

Electric power stations can also operate on fuel cells with solid oxide electrolyte.

Piezoelectric generators are known that receive energy thanks to kinetic energy (walking paths, speed bumps, turnstiles and even dance floors already exist with this technology).

There are also nanogenerators that are aimed at converting energy in the human body itself into electrical energy.

What can you say about algae that is used to heat houses, football swords that generate electrical energy, bicycles that can charge gadgets, and even finely chopped paper that is used as a current source?

Enormous prospects, of course, lie in the development of volcanic energy.

All this is the reality of today, which scientists are working on. It is quite possible that some of them will very soon become a completely commonplace phenomenon, like electricity in homes today.

Or maybe someone will reveal the secrets of the scientist Nikola Tesla, and humanity will be able to easily obtain electricity from the ether?

This article will describe methods for producing electric current, their types, advantages and disadvantages. In general terms, current sources can be divided into mechanical, chemical and those using other physical transformations.

Chemical current sources

Chemical current sources convert the chemical reactions of an oxidizer and a reducer into an emf. The first chemical current source was invented by Alessandro Volta in 1800. Subsequently, his invention was called the "Volta Element". The voltaic elements connected into a vertical battery make up a voltaic column.

In 1859, the French physicist Gston Plante invented the lead-acid battery. It consisted of lead plates placed in sulfuric acid. This type of battery is still widely used, for example in cars.

In 1965, the French chemist J. Leclanche proposed an element consisting of a zinc cup with an ammonium chloride solution, into which a manganese oxide agglomerate with a carbon conductor was placed. This element became the progenitor of modern salt batteries.

All chemical elements are based on 2 electrodes. One of them is an oxidizing agent, and the other is a reducing agent, both are in contact with the electrolyte. An EMF occurs between the electrodes. At the anode, the reducing agent is oxidized; electrons pass through the external circuit to the cathode and participate in the reduction reaction of the oxidizing agent. Thus, the flow of electrons passes through the external circuit from the negative pole to the positive one. Lead is used as a reducing agent. cadmium, zinc and other metals. Oxidizing agents - lead oxide, manganese oxide, nickel hydroxide and others. As an electrolyte, solutions of alkalis, acids and salts are used.

There are also fuel cells in which the oxidizing agent and reducing agent are supplied externally. An example is a hydrogen-oxygen fuel cell, which works on the same principle as an electrolyzer, only in reverse - hydrogen and oxygen are supplied to the plates, and electricity is generated by the reaction of their combination into water.

Mechanical current sources

Mechanical current sources include all sources that convert mechanical energy into electrical energy. Usually, direct transformations are not used, but through other energy, usually magnetic. For example, a magnetic field rotates in generators - created by magnets, or otherwise excited, acting on the windings it creates an EMF.

E.H. Lenz discovered back in 1833 that electric motors with permanent magnets could generate electricity if the rotor was spun. As part of the commission for testing the Jacobi electric motor, he experimentally proved the reversibility of the electric motor. It was later discovered that the energy generated by the generator can be used to power its own electromagnets.

The first generator was built in 1832 by inventors from Paris, the Pixin brothers. The generator used a permanent magnet, the rotation of which generated an EMF in nearby windings. In 1843, Emil Stehrer also built a generator consisting of 3 magnets and 6 coils. All early generators used permanent magnets. Later (1851-1867) electromagnets were used, powered by a built-in permanent magnet generator. Such a machine was created by Henry Wilde in 1863.

An unused but still existing method using piezoceramics can also be classified as mechanical. The piezo emitter is also reversible and can generate energy under mechanical influence.

Other power sources

The most commonly used non-mechanical power source today is a solar battery. A solar battery directly converts light into electricity by knocking out electrons in a pn junction with photon energy. The most commonly used solar cells are silicon based. They are produced by doping the same semiconductor with various impurities to create np junctions.

Also, in field conditions, Peltier elements are often used. The Peltier element creates a temperature difference when electric current flows. The opposite effect, the Seebeck effect, is used to produce an electric current when a temperature difference is applied to an element. Due to the use of different conductors, the temperature of each is different, which leads to the flow of electrons from a hotter conductor to a less heated one.

Current sources, 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 batteries (galvanic cells and batteries) dates back to the 19th century. (for example, Volta battery, Leclanche cell). However, until the 40s. 20th century In the world, no more than 5 types of galvanic pairs have been developed and implemented in designs. From the mid-40s. As a result of the development of radio electronics and the widespread use of autonomous electrical generators, about 25 more types of galvanic pairs have been created. Theoretically, the free energy of chemical reactions of almost any oxidizing agent and reducing agent can be realized in electrical energy, and therefore, the implementation of several thousand galvanic pairs is possible. The operating principles of most physical electronic technologies were already known in the 19th century. Subsequently, due to rapid development and improvement, turbogenerators and hydrogenerators became the main industrial sources of electricity. Physical technologies based on other principles received industrial development only in the 50s and 60s. 20th century, which is due to the increased and rather specific requirements of modern technology. In the 60s technically developed countries already had industrial samples of thermogenerators, thermionic generators (USSR, Germany, USA), nuclear batteries

Chemical current sources It is customary to call devices that generate electric current using the energy of redox reactions of chemical reagents. In accordance with the operating scheme and the ability to supply energy to the electrical network, chemical generators are divided into primary, secondary, and backup, as well as electrochemical generators.

Physical current sources are devices that convert thermal, mechanical, electromagnetic energy, as well as the energy of radiation and nuclear decay into electrical energy. In accordance with the most commonly used classification, physical generators include: electric machine generators, thermoelectric generators, thermionic converters, MHD generators, as well as generators that convert the energy of solar radiation and atomic decay

To maintain an electric current in a conductor, some external source of energy is needed, which would always maintain a potential difference at the ends of this conductor.
Such energy sources are the so-called sources of electric current, which have a certain electromotive force that creates and maintains a potential difference at the ends of the conductor for a long time.

Numerically, electromotive force is measured by the work done by a source of electrical energy when transferring a single positive charge throughout a closed circuit.

If the energy source, performing work A, ensures the transfer of charge q throughout the closed circuit, then its electromotive force (E) will be equal to

Internal resistance of the current source- a quantitative characteristic of a current source, which determines the amount of energy losses when passing through the source of electric current.
Internal resistance has the dimension of resistance and is measured in Ohms.
When an electric current passes through a source, the same processes of energy dissipation occur as when passing through a load resistance. Thanks to these processes, the voltage at the terminals of the current source is not equal to the electromotive force, but depends on the magnitude of the current, and, consequently, on the load. At small current values, this dependence is linear and can be represented in the form

8) Power and efficiency source is equal to the ratio of the voltage in the external circuit to the magnitude of the emf. Electric power- a physical quantity characterizing the speed of transmission or conversion of electrical energy. Net power varies depending on external resistance in a more complex manner. Indeed, Puseful = 0 at extreme values ​​of external resistance: at R = 0 and R®¥. Thus, the maximum useful power should occur at intermediate values ​​of external resistance.

9) Chemical current source (abbr. HIT) is a source of EMF in which the energy of the chemical reactions occurring in it is directly converted into electrical energy.

Operating principle: Chemical current sources are based on two electrodes (a negatively charged anode containing a reducing agent and a positively charged cathode containing an oxidizing agent) in contact with the electrolyte. A potential difference is established between the electrodes - an electromotive force corresponding to the free energy of the redox reaction. The action of chemical current sources is based on the occurrence of spatially separated processes in a closed external circuit: at the negative anode, the reducing agent is oxidized, the resulting free electrons pass through the external circuit to the positive cathode, creating a discharge current, where they participate in the reduction reaction of the oxidizing agent. Thus, the flow of negatively charged electrons through the external circuit goes from the anode to the cathode, that is, from the negative electrode (the negative pole of the chemical current source) to the positive. This corresponds to the flow of electric current in the direction from the positive pole to the negative, since the direction of the current coincides with the direction of movement of positive charges in the conductor.

Modern chemical current sources use:

· as a reducing agent (anode material) - lead Pb, cadmium Cd, zinc Zn and other metals;

· as an oxidizing agent (cathode material) - lead(IV) oxide PbO 2, nickel hydroxide NiOOH, manganese(IV) oxide MnO 2 and others;

· as an electrolyte - solutions of alkalis, acids or salts.

2) Manganese-zinc (MC) dry elements with a depolarizer of manganese dioxide have become widespread.
A cup-type dry cell (Fig. 3) has a rectangular or cylindrical zinc vessel, which is a negative electrode. A positive electrode in the form of carbon is placed inside it.
sticks or plates, which are located in a bag filled with a mixture of manganese dioxide with coal or graphite powder. Carbon or graphite is added to reduce resistance. The carbon rod and the bag with the depolarizing mass are called an agglomerate. A paste composed of ammonia (NH4Cl), starch and some other substances is used as an electrolyte. For cup elements, the central terminal is the positive pole.

Lead acid batteries are the most common among secondary chemical power sources, possessing relatively high power combined with reliability and relatively low cost. These batteries find a variety of practical applications. They owe their popularity and wide scale of production to starter batteries intended for various vehicles and, above all, cars. In this area, their monopoly position is stable and lasts for a long time. The vast majority of stationary and a significant part of carriage batteries are equipped with lead batteries. Lead-acid batteries successfully compete with alkaline traction batteries.

Lezo-nickel battery is a secondary chemical current source in which iron is the anode, the electrolyte is an aqueous solution of sodium or potassium hydroxide (with lithium hydroxide additives), and the cathode is nickel(III) oxide hydrate.

The active material is contained in nickel-plated steel tubes or perforated pockets. In terms of cost and specific energy consumption, they are close to lithium-ion batteries, and in terms of self-discharge, efficiency and voltage - to NiMH batteries. These are quite durable batteries, resistant to rough handling (overcharge, deep discharge, short circuit and thermal shock) and have a very long service life.

Their use has been declining since Edison's factory/lab fire stopped production in 1914, due to poor battery performance at low temperatures, poor charge retention, and high production costs comparable to the best sealed lead-acid batteries and up to 1 /2 the cost of NiMH batteries. However, due to the rise in the cost of lead in recent years, which has caused the price of lead batteries to rise significantly, prices have almost become equal.

When comparing batteries with lead-acid batteries, it should be remembered that the permissible operational discharge of a lead-acid battery is several times less than the theoretical full capacity, and that of an iron-nickel battery is very close to it. Therefore, the actual operational capacity of an iron-nickel battery, with an equal theoretical full capacity, can be several times (depending on the mode) greater than that of a lead-acid battery.

10) Electrical generators of direct and alternating current.

Machines that convert mechanical energy into electrical energy are called generators.
The simplest direct current generator (Fig. 1) is a frame of conductor placed between the poles of a magnet, the ends of which are connected to insulated half rings called collector plates. Positive and negative brushes are pressed against the half rings (collector), which are closed by an external circuit through a light bulb. For the generator to operate, the conductor frame with the collector must be rotated. In accordance with the right-hand rule, when the frame of the conductor with the collector rotates, an electric current will be induced in it, changing its direction every half turn, since the magnetic lines of force on each side of the frame will intersect in one direction or the other. At the same time, every half turn the contact of the ends of the frame conductor and the commutator half-rings with the generator brushes changes. The current will flow into the external circuit in one direction, changing only in value from 0 to maximum. Thus, the collector in the generator serves to rectify the alternating current generated by the frame. In order for the electric current to be constant not only in direction, but also in magnitude (approximately constant in magnitude), the collector is made of many (36 or more) plates, and the conductor consists of many frames or sections made in the form of an armature winding .

Rice. 1. Diagram of the simplest direct current generator: 1 - half ring or collector plate; I - conductor frame; 3 - generator brush

The basic structure of the simplest alternating current generator is shown in Fig. 4. In this generator, the ends of the conductor frame are each connected to its own ring, and the generator brushes are pressed against the rings. The brushes are closed by an external circuit through a light bulb. When the frame with rings rotates in a magnetic field, the generator will produce an alternating current that changes in magnitude and direction every half turn. This alternating current is called single-phase. In technology, generators of three-