Electric current, sources of electric current: definition and essence. Current source - classification and purpose Main types of electric current sources
When talking about the use of electrical energy in everyday life, in production or transport, then they mean the operation of electricalcurrent Electric current is supplied to the consumer from the power plantby wire. Therefore, when the houses suddenly go outelectric lamps or the movement of electric trains stops,trolleybuses, they say that the current has disappeared in the wires.
In order for an electric current to exist in conductors for a long time, it is necessary to maintain an electric field in it all this time. An electric field in conductors is created and can be maintained for a long time by sources of electric current.
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, which accumulate at the poles of the source. The separated particles accumulate at the poles of the current source. This is the name of the places to which conductors are connected using terminals or clamps. One pole of the current source is charged positively, the other - negatively. If the poles of the source are connected by a conductor, then under the influence of an electric field, free charged particles in the conductor will begin to move in a certain direction, and an electric current will arise.
There are different types of current sources:
Mechanical current source
Mechanical energy is converted into electrical energy.
These include: an electrophore machine (the disks of the machine are driven into rotation in opposite directions. As a result of the friction of the brushes on the disks, charges of the opposite sign accumulate on the conductors of the machine), a dynamo, and generators.
Thermal current source
Internal energy is converted into electrical energy.
For example, a thermoelement - two wires made of different metals must be soldered at one end, then the place of the junction must be heated, then a voltage will appear between the other ends of these wires.
Used in temperature sensors and geothermal power plants.
Light current source
Light energy is converted into electrical energy.
For example, a photocell - when certain semiconductors are illuminated, light energy is converted into electrical energy. Solar batteries are made from photocells.
They are used in solar batteries, light sensors, calculators, and video cameras.
Chemical current source
As a result of chemical reactions, internal energy is converted into electrical energy.
Galvanic cells are the most common sources of direct current in the world. Their advantage is ease and safety of use. Batteries were invented a long time ago, at the dawn of the development of electricity. Back then they didn’t know how to transmit current over long distances; they used it only within the laboratory. But to this day, various battery options have not lost their relevance. There are disposable and reusable batteries - accumulators.
Disposable batteries exhaust their full potential during use and are no longer suitable.
In everyday life, batteries are often used that can be recharged many times - accumulators (from the Latin word accumulator - to accumulate). The simplest battery consists of two lead plates (electrodes) placed in a sulfuric acid solution.
For the battery to become a source of current, it must be charged. To charge, direct current from some source is passed through the battery. During the charging process, as a result of chemical reactions, one electrode becomes positively charged and the other negatively charged. When the battery is charged, it can be used as an independent power source. The battery poles are marked with “+” and “-” signs. When charging, the positive pole of the battery is connected to the positive pole of the current source, and the negative pole is connected to the negative pole.
Electric current is the directed, ordered movement of electric charges.
Electric charges can be different. These can be electrons or ions (positively or negatively charged).
To obtain an electric current in a conductor, you need to create an electric field in it. Under the influence of the field, electric charges will begin to move, and an electric current will arise.
Pay attention!
Conditions for the existence of electric current:
The presence of free electrical charges;
the presence of an electric field that ensures the movement of charges;
closed electrical circuit.
The electric field is created by sources of electric current.
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.
There are different types of current sources:
Mechanical current source- mechanical energy is converted into electrical energy. These include: electrophoric machine, dynamo, generators.
The disks of the electrophore machine are rotated in opposite directions. As a result of the friction of the brushes on the discs, charges of the opposite sign accumulate on the conductors of the machine.
Thermal current source- internal energy is converted into electrical energy.
This includes a thermocouple. Two wires of different metals are soldered at one end. Then the junction is heated, then voltage appears between the other ends of these wires.
Light current source- light energy is converted into electrical energy. This includes a photocell.
When some semiconductors are illuminated, light energy is converted into electrical energy. Solar batteries are made from photocells.
Chemical current source- as a result of chemical reactions, internal energy is converted into electrical energy.
This includes, for example, a galvanic cell.
A carbon rod U is inserted into a zinc vessel C, which has a metal lid M. The rod is placed in a linen bag filled with a mixture of manganese oxide and carbon C. The space between the zinc body and the mixture of manganese oxide with carbon is filled with a jelly-like solution of salt R. As a result of a chemical reaction The zinc becomes negatively charged and the carbon rod acquires a positive charge. An electric field arises between the charged rod and the zinc vessel. In such a current source, the carbon is the positive electrode, and the zinc vessel is the negative electrode.
A battery can be made from several galvanic cells.
Current sources based on galvanic cells are used in household autonomous electrical appliances and uninterruptible power supplies. They are disposable. In everyday life, batteries are often used that can be recharged many times. They are called batteries.
The simplest battery consists of a vessel filled with a weak solution of sulfuric acid in water, into which two lead plates (electrodes) are lowered. In order for the battery to become a source of current, it must be charged. If both plates are connected to the poles of any source of electrical energy, then the electric current passing through the solution will charge one electrode positively and the other negatively. Such batteries are called acid or lead batteries. In addition to them, there are also alkaline or nickel-iron batteries. They use an alkali solution and plates: one is made of compressed iron powder, and the second is made of nickel peroxide.
Batteries are used in cars, electric vehicles, cell phones, railroad cars, and even artificial Earth satellites.
Along with current sources, there are various consumers of electricity: lamps, vacuum cleaners, computers and many others. To deliver electricity from the source to the consumer, connecting conductors are needed, and in order for its supply to be controlled, switches, switches, buttons, etc. are needed.
Pay attention!
The source of electricity, consumers of electricity, closing devices connected to each other by wires are called an electrical circuit.
For an electric current to exist in a circuit, it must be closed, i.e. consist of conductors of electricity. If the wire breaks at any point, the current in the circuit will stop. The operation of switches is based on this.
Pay attention!
Drawings that depict methods of connecting electrical devices into a circuit are called diagrams.
Devices on the diagrams are indicated by conventional symbols. Here are some of them:
Galvanic cell or battery | Battery cells and batteries | Incandescent light bulb | Electric bell | Resistor |
|
Engine | Generator | Crossing wires without connection | Connecting wires |
|||
A current source is a device that converts various types of energy into electricity. Such sources can be roughly divided into physical and chemical.
Current source and its history
The first chemical galvanic cells and batteries appeared in the nineteenth century (Leclanche cells and Volta batteries). However, until approximately the forties of the twentieth century, the advantages provided by the current source were not actually used. There were only a few galvanic pairs. But literally since the mid-forties, thanks to the rapid development of radio electronics, almost three dozen new types of pairs of galvanic elements have appeared. Theoretically, a current source is the realization of the free energy of almost any chemical reaction of a reducing agent and an oxidizing agent. Therefore, it is possible to implement more than a thousand galvanic pairs. The physical current source became widespread in industry in the early sixties of the last century. This is due to the specific requirements of technology in production. By the end of the sixties, most technologically advanced countries had thermal generators, thermionic generators and nuclear batteries.
Current source and its main characteristics
Technological progress has stimulated the development of power supplies, especially autonomous ones. The current source today can be found in portable lighting devices, radios, tape recorders, televisions, medical equipment, cars, airplanes, tractors, spacecraft and many other things. The main characteristics and parameters of electricity sources can be called: energy intensity, specific energy intensity, rated and specific power, efficiency (efficiency factor), service life, reliability, frequency, overload capacity, voltage, rated current, cost.
Types of current sources
In accordance with the ability to accumulate energy, chemical sources are divided into primary, backup, secondary and electrochemical generators. There is also a current source using a field-effect transistor. Each type should be considered in more detail.
Primary current source
Such sources allow only one-time use of the chemical energy of the reagents. The cathode (positive electrode) and anode (negative electrode) are separated in a liquid or paste state by an electrolyte. Both the cathode and the anode have a galvanic connection with each other.
Secondary current source
Such batteries or rechargeable batteries allow the repeated use of chemical energy, from hundreds of times to tens of thousands of cycles. The electrolyte and electrodes are constantly in a state of electrical contact with each other. To date, specific storage conditions for such batteries have been developed.
Backup current source
Although standby sources allow only one cycle, the electrolyte and electrodes are not galvanically connected. They are stored either in a liquid state (in metal or glass ampoules) or in a hard solid state.
Current source - it's easy!
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, which accumulate at the poles of the source and create an electric field between them.
If the poles of the source are connected with wires, then an electric current will flow through them.
There are different types of current sources:
Mechanical current source
Mechanical energy is converted into electrical energy.
These include: an electrophore machine (the machine’s disks are rotated in opposite directions.
As a result of the friction of the brushes on the disks, charges of the opposite sign accumulate on the conductors of the machine), dynamo, generators.
Thermal current source
Internal energy is converted into electrical energy.
For example, a thermoelement - two wires made of different metals need to be soldered at one end, then the junction is heated, then a voltage will appear between the other ends of these wires.
Used in temperature sensors and geothermal power plants.
Light current source
Light energy is converted into electrical energy.
For example, a photocell - when certain semiconductors are illuminated, light energy is converted into electrical energy. Solar batteries are made from photocells.
They are used in solar batteries, light sensors, calculators, and video cameras.
Chemical current source
As a result of chemical reactions, internal energy is converted into electrical energy.
Galvanic cell- a carbon rod is inserted into a zinc vessel. The rod is placed in a linen bag filled with a mixture of manganese oxide and carbon. The element uses a flour paste with ammonia solution.
When ammonia interacts with zinc, the zinc acquires a negative charge, and the carbon rod acquires a positive charge. An electric field arises between the charged rod and the zinc vessel. In such a current source, the carbon is the positive electrode, and the zinc vessel is the negative electrode.
In a galvanic cell, the electrodes must interact differently with the solution. Therefore, electrodes are made from different materials.
A battery can be made from several galvanic cells.
What does it mean the battery is dead?
This means that the electrodes or solution in the galvanic cell have already been used up. The galvanic cell (battery) should be replaced with a new one.
Current sources based on galvanic cells are used in household autonomous electrical appliances and uninterruptible power supplies.
Batteries
Batteries are chemical sources of current in which electrodes are not consumed.
For example, the simplest battery consists of two lead plates immersed in a sulfuric acid solution.
Before use, the battery must be charged, i.e. connect the battery poles with similar poles of some current source. When charging, the chemical energy of the battery increases.
After use, a discharged battery can be charged again. When a battery discharges, it converts chemical energy into electrical energy.
Batteries are either acidic or alkaline.
Batteries can be assembled from individual batteries.
Batteries are used when it is more profitable to recharge the current source than to replace it with a new one.
For example, in space, batteries are charged from solar panels. When discharged, they power the spacecraft equipment.
LEGEND
Symbol of the current source on the electrical diagram
or a battery consisting of several sources
BOOKSHELF
FROM THE HISTORY OF INVENTION
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 inside living organisms
Curiosities in science.
The wife of anatomy professor at the University of Bologna Luigi Galvani, who had a cold, required care and attention. Doctors prescribed her a “strengthening broth” made from frog legs. While preparing frogs for broth, Galvani discovered the famous “living electricity” - electric current.
The Leyden jar is the first source of current.
By the middle of the 18th century. In Holland, at the University of Leiden, scientists under the leadership of Pieter van Muschenbrouck found a way to accumulate electrical charges. Such a storage device for electricity was a Leyden jar - a glass vessel, the walls of which were lined with lead foil on the outside and inside. A Leyden jar, connected by its plates to an electric machine, could accumulate and store a significant amount of electricity for a long time. The discharge of the Leyden jar had sufficient power. 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.
This discovery made a huge impression on all people, even those completely far from science. Everyone wanted to experience the electric discharge on themselves and see its effect on others. The inventors of the Leyden jar, Kleist and Muschenbreck, were the first to experience the shock of charges: the first of them, after the test, did not want to repeat the sensation even for the Persian throne, the second agreed to suffer for the sake of science.
Doctors also took up the Leyden jars. In 1744, Kratzenstein from Halle cured the paralysis of a finger with a discharge, then Gilbert breathed life into the carpenter’s hand, which had become numb from the blow of a hammer. The audience groaned with anticipation, everyone wanted immortality.
Invention of the galvanic cell.
The first electric battery appeared in 1799.
It was invented by the Italian physicist Alessandro Volta (1745 - 1827) - Italian physicist, chemist and physiologist, inventor of a source of direct electric current.
One day he picked up physiologist Luigi Galvani’s treatise “On Electrical Forces in Muscle” and realized that a frog’s leg began to twitch only when it was touched with two different metals. Galvani didn't notice this! Volta decides to try Galvani's experiment on himself: he took two coins from different metals and put them in his mouth - on top, on the tongue, and under it. Then he connected the coins with a thin wire and tasted the salted water.
Volta knew very well that this is the taste of electricity, and it was born from metals.
This is how the simplest Volta element works:
Volta's first current source, the “voltaic pole,” was built in strict accordance with his theory of “metallic” electricity. Volta alternately placed several dozen small zinc and silver circles on top of each other, placing paper moistened with salted water between them.
Volta was also the first tester of his device. The scientist lowered his hand into a bowl of water, to which he connected one of the contacts of the “pillar”, and attached a wire to the other contact, with the free end of which he touched his forehead, nose, and eyelid. He felt either a prick or a sharp blow - and he carefully recorded all this. Sometimes the pain became unbearable - and then Volta opened his chain. He realized that his “pillar” was a source of direct current.
In 1800, a letter from Volta appeared in the journal of the Royal Society of London describing the “Voltaic Column.” This is how the world's first electric battery was invented. Although the power of the Voltaic column would only be enough to light just one weak lamp.
And the famous Russian scientist Petrov in 1802 made a huge battery. It consisted of 4,200 copper and zinc circles, between each pair of which cardboard circles soaked in ammonia solution were placed. This battery consisted of 2100 copper-zinc galvanic cells connected in series. The voltage at its terminals was about 1650-1700 V.
It was the first relatively high-voltage direct current source in history.
DO IT YOURSELF
Thermocouple from an electric lamp
If you take an electric lamp without a glass cylinder, screw it into a socket mounted on a stand and connect it to a galvanometer, then when a burning match heats the junction of the spiral with the wire, the galvanometer will show the presence of current.
Leyden jar
A Leyden jar (or capacitor) is easy to make yourself. For this you need a glass jar.
The walls of the jar on the outside and inside should be covered 2/3 with foil (no folds!). Then take a plastic lid and insert a metal rod into the middle of it. Place a metal (or any other material, but covered with foil) ball on the upper end of the rod. Make a brush out of foil and attach it to the lower end of the rod so that it touches the bottom when the lid is closed. Close the jar with a lid - and the device is ready!
To charge the jar, touch the ball with, for example, an electrified plastic comb. To increase the charge, do this several times, re-electrifying the comb.
Cultures of some organisms are capable of producing electric current. If a platinum electrode is placed in a liquid culture of E. coli or ordinary yeast, and another in the same nutrient medium, but without microbes, then a potential difference arises
"REVIVING" THE BATTERY!
Do not rush to throw away the old battery, but try to “revive” it.
In manganese-zinc cells, over time, manganese dioxide forms manganese hydroxide, which gradually coats the oxide and interferes with the chemical reaction. The easiest way is to knock on the battery, for example, with a stone (when shaken, the resulting surface layer of hydroxide is destroyed).
Or you can punch a hole in the zinc battery cup, for example, with a nail and lower the battery into water. The electrolyte dilutes, and it is easier for it to penetrate to manganese dioxide. In this way, you can increase the battery life by almost a third.
HOMEMADE BATTERIES
Delicious battery
And you can verify this without a voltmeter: touch copper and zinc with your tongue at the same time - your tongue will tingle!
You can create a large battery by connecting the elements in series.
Delicious, isn't it?!
Soda battery
You need to dilute baking soda to the consistency of sour cream, and place a teaspoon on a saucer. Place a copper coin on one edge of the soda lump, and a piece of galvanized iron on the other end. You have a galvanic cell that produces a voltage of about 1V. It can be measured using a voltmeter by touching the wires coming from the voltmeter to copper and zinc at the same time. You can make a series circuit of several similar elements, the voltage at the battery output will increase!
Salty battery
Take five “yellow” and “white” coins. Lay them out, alternating between each other. Place between them pads made of blotter or newspaper soaked in a strong solution of table salt. Stack it all up and squeeze it together. The battery is ready! Connect a voltmeter to the first “yellow” and the last “white” coin. There is tension! And if you take this column of coins with your thumb and forefinger, you can feel a slight electric shock!
Don’t forget to first clean all metal parts from grease; this works very well with the help of Pemoxol powder (for cleaning dishes)!
"DRY" or "WET"?
Is the so-called “dry element” really dry?
Not at all, the cavity of the element between the electrodes is filled with a substance in a paste-like state, and so that it does not leak out and the electrodes do not move, the element is filled with resin on top.
Carbon-zinc electroplated batteries are the most common dry batteries. In them, the electrolyte is in a paste-like state.
Carbon-zinc elements can be "regenerated" during a break in operation,
and as a result of periodic “rest”, the service life of the element is extended.
Well well
In remote villages, on farmsteads where there is no electricity, you can find an interesting kerosene lamp - a “power plant”: it not only gives light, but also generates electrical energy. Its device is quite simple. Blocks of two different semiconductor materials are mounted in the form of a tube, which is placed on a shortened lamp glass. Each pair of different bars is soldered together with a metal plate, forming the letter P. When the lamp is lit, . the adhesions are heated, the sides of the bars facing the inside of the tube are heated by the air rising from the flame. The opposite edges remain cold. As a result, a positive charge accumulates at the cold end of one block, and a negative charge accumulates at the cold edge of the other block. By connecting the edges of the corresponding pairs with wire, we obtain a thermoelectric generator.
So far, in our time, such devices do not find industrial use, because The efficiency of such a thermocouple is low - only 6-8%. This is several times less than the efficiency of modern thermal power plants.
The wind farm in Altamont Pass (California) consists of 300 wind turbines. To produce the same amount of electricity as a nuclear power plant, a wind farm would need to cover an area of approximately 140 square miles.
TRY TO DISCOVER
(or problems "for 5")
1. How will the action of the Volta element change if its copper electrode is replaced with zinc or the zinc electrode is replaced with a second copper one?
2. If an aluminum kettle containing a solution of table salt is connected
copper wire is connected to one terminal of the galvanometer, and an iron glass is connected to the second terminal, what happens when you pour liquid from a teapot into a glass?
