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Without electricity it is impossible to imagine life modern man. Volts, Amps, Watts - these words are heard in a conversation about devices that run on electricity. But what is this electric current and what are the conditions for its existence? We will discuss this further by providing short explanation for beginner electricians.

Definition

An electric current is a directed movement of charge carriers - this is a standard formulation from a physics textbook. In turn, certain particles of matter are called charge carriers. They may be:

• Electrons are negative charge carriers.
• Ions are positive charge carriers.

But where do charge carriers come from? To answer this question, you need to remember the basic knowledge about the structure of matter. Everything that surrounds us is matter, it consists of molecules, its smallest particles. Molecules are made up of atoms. An atom consists of a nucleus around which electrons move in given orbits. Molecules also move randomly. The movement and structure of each of these particles depends on the substance itself and the influence of the environment on it, such as temperature, stress, and so on.

An ion is an atom in which the ratio of electrons and protons has changed. If the atom is initially neutral, then the ions, in turn, are divided into:

• Anions are the positive ion of an atom that has lost electrons.
• Cations are an atom with "extra" electrons attached to the atom.

The unit of current is Ampere, according to it is calculated by the formula:

where U is voltage [V] and R is resistance [Ohm].

Or directly proportional to the amount of charge transferred per unit of time:

where Q is the charge, [C], t is the time, [s].

Conditions for the existence of an electric current

We figured out what electric current is, now let's talk about how to ensure its flow. For electric current to flow, two conditions must be met:

1. The presence of free charge carriers.
2. Electric field.

The first condition for the existence and flow of electricity depends on the substance in which the current flows (or does not flow), as well as its state. The second condition is also feasible: for the existence of an electric field, the presence of different potentials is necessary, between which there is a medium in which charge carriers will flow.

Recall: Voltage, EMF is a potential difference. It follows that in order to fulfill the conditions for the existence of current - the presence of an electric field and an electric current, voltage is needed. These can be plates of a charged capacitor, a galvanic cell, an EMF that has arisen under the influence of a magnetic field (generator).

We figured out how it arises, let's talk about where it is directed. The current, in its usual use, moves in conductors (wiring in an apartment, incandescent bulbs) or in semiconductors (LEDs, your smartphone's processor and other electronics), less often in gases (fluorescent lamps).

So, in most cases, the main charge carriers are electrons, they move from minus (a point with a negative potential) to a plus (a point with a positive potential, you will learn more about this below).

But an interesting fact is that the direction of current movement was taken to be the movement of positive charges - from plus to minus. Although in fact the opposite is happening. The fact is that the decision on the direction of the current was made before studying its nature, and also before it was determined due to which the current flows and exists.

Electric current in different environments

We have already mentioned that in different media the electric current can differ in the type of charge carriers. Media can be divided according to the nature of conductivity (in descending order of conductivity):

1. Conductor (metals).
2. Semiconductor (silicon, germanium, gallium arsenide, etc.).
3. Dielectric (vacuum, air, distilled water).

in metals

Metals contain free charge carriers and are sometimes referred to as "electric gas". Where do free charge carriers come from? The fact is that metal, like any substance, consists of atoms. Atoms somehow move or oscillate. The higher the temperature of the metal, the stronger this movement. At the same time, the atoms themselves general view remain in their places, actually forming the structure of the metal.

In the electron shells of an atom, there are usually several electrons that have a rather weak bond with the nucleus. Under the influence of temperatures, chemical reactions and the interaction of impurities, which are in any case in the metal, electrons are detached from their atoms, positively charged ions are formed. The detached electrons are called free and move randomly.

If they are affected by an electric field, for example, if you connect a battery to a piece of metal, the chaotic movement of electrons will become ordered. Electrons from a point to which a negative potential is connected (the cathode of a galvanic cell, for example) will begin to move towards a point with a positive potential.

in semiconductors

Semiconductors are materials in which normal condition no free charge carriers. They are in the so-called forbidden zone. But if external forces are applied, such as an electric field, heat, various radiations (light, radiation, etc.), they overcome the band gap and pass into the free band or conduction band. Electrons break away from their atoms and become free, forming ions - positive charge carriers.

Positive carriers in semiconductors are called holes.

If you simply transfer energy to a semiconductor, for example, heat it, a chaotic movement of charge carriers will begin. But if we are talking about semiconductor elements, such as a diode or a transistor, then at the opposite ends of the crystal (a metallized layer is applied to them and the leads are soldered), an EMF will appear, but this does not apply to the topic of today's article.

If you apply an EMF source to a semiconductor, then charge carriers will also move into the conduction band, and their directed movement will also begin - holes will go to the side with a lower electric potential, and electrons - to the side with a larger one.

In vacuum and gas

A vacuum is a medium with a complete (ideal case) absence of gases or a minimized (in reality) its amount. Since there is no matter in vacuum, there is no source for charge carriers. However, the flow of current in a vacuum marked the beginning of electronics and a whole era of electronic elements - vacuum tubes. They were used in the first half of the last century, and in the 50s they began to gradually give way to transistors (depending on the specific field of electronics).

Let's assume that we have a vessel from which all the gas has been pumped out, i.e. it is a complete vacuum. Two electrodes are placed in the vessel, let's call them an anode and a cathode. If we connect the negative potential of the EMF source to the cathode, and positive to the anode, nothing will happen and the current will not flow. But if we start heating the cathode, the current will start to flow. This process is called thermionic emission - the emission of electrons from a heated surface of an electron.

The figure shows the process of current flow in a vacuum lamp. In vacuum tubes, the cathode is heated by a nearby filament in Fig. (H), such as that found in a lighting lamp.

At the same time, if you change the polarity of the supply - apply a minus to the anode, and apply a plus to the cathode - the current will not flow. This will prove that the current in vacuum flows due to the movement of electrons from the CATHODE to the ANODE.

A gas, like any substance, consists of molecules and atoms, which means that if the gas is under the influence of an electric field, then at a certain strength (ionization voltage), the electrons will come off the atom, then both conditions for the flow of electric current will be met - the field and free media.

As already mentioned, this process is called ionization. It can occur not only from the applied voltage, but also when the gas is heated, x-rays, under the influence of ultraviolet and other things.

Current will flow through the air, even if a burner is installed between the electrodes.

The flow of current in inert gases is accompanied by gas luminescence; this phenomenon is actively used in fluorescent lamps. The flow of electric current in a gaseous medium is called a gas discharge.

in liquid

Let's say that we have a vessel with water in which two electrodes are placed, to which a power source is connected. If the water is distilled, that is, pure and does not contain impurities, then it is a dielectric. But if we add a little salt, sulfuric acid, or any other substance to the water, an electrolyte is formed and a current begins to flow through it.

An electrolyte is a substance that conducts electricity by dissociating into ions.

If copper sulfate is added to water, then a layer of copper will settle on one of the electrodes (cathode) - this is called electrolysis, which proves that the electric current in the liquid is carried out due to the movement of ions - positive and negative charge carriers.

Electrolysis is a physical and chemical process, which consists in the separation of the components that make up the electrolyte on the electrodes.

Thus, copper plating, gilding and coating with other metals occur.

Conclusion

To summarize, for the flow of electric current, free charge carriers are needed:

• electrons in conductors (metals) and vacuum;
• electrons and holes in semiconductors;
• ions (anions and cations) in liquids and gases.

In order for the movement of these carriers to become ordered, an electric field is needed. In simple words- apply voltage at the ends of the body or install two electrodes in an environment where electric current is expected to flow.

It is also worth noting that the current in a certain way affects the substance, there are three types of exposure:

• thermal;
• chemical;
• physical.

Useful

". Today I want to touch on such a topic as electric current. What is it? Let's try to remember the school curriculum.

Electric current is the ordered movement of charged particles in a conductor.

If you remember, in order for charged particles to move, (an electric current arises) you need to create an electric field. To create an electric field, you can carry out such elementary experiments as rubbing a plastic handle on wool and for some time it will attract light objects. Bodies capable of attracting objects after rubbing are called electrified. We can say that the body in this state has electric charges, and the bodies themselves are called charged. From the school curriculum, we know that all bodies are made up of tiny particles (molecules). A molecule is a particle of a substance that can be separated from a body and it will have all the properties inherent in this body. The molecules of complex bodies are formed from various combinations atoms of simple bodies. For example, a water molecule consists of two simple ones: an oxygen atom and one hydrogen atom.

Atoms, neutrons, protons and electrons - what are they?

In turn, an atom consists of a nucleus and revolving around it electrons. Each electron in an atom has a small electrical charge. For example, a hydrogen atom consists of a nucleus of an electron revolving around it. The nucleus of an atom consists, in turn, of protons and neutrons. The nucleus of an atom, in turn, has an electric charge. The protons that make up the nucleus have the same electric charges and electrons. But protons, unlike electrons, are inactive, but their mass is many times greater than the mass of an electron. The particle neutron, which is part of the atom, has no electric charge, it is neutral. The electrons that revolve around the nucleus of an atom and the protons that make up the nucleus are carriers of equal electric charges. Between the electron and the proton there is always a force of mutual attraction, and between the electrons themselves and between the protons, the force of mutual repulsion. Because of this, the electron has a negative electric charge, and the proton positive. From this we can conclude that there are 2 kinds of electricity: positive and negative. The presence of equally charged particles in an atom leads to the fact that between the positively charged nucleus of the atom and the electrons rotating around it, there are forces of mutual attraction that hold the atom together. Atoms differ from each other in the number of neutrons and protons in the nuclei, which is why the positive charge of the nuclei of atoms of various substances is not the same. In atoms of different substances, the number of rotating electrons is not the same and is determined by the positive charge of the nucleus. The atoms of some substances are firmly bound to the nucleus, while in others this bond can be much weaker. This explains the different strengths of the bodies. Steel wire is much stronger than copper wire, which means that steel particles are more strongly attracted to each other than copper particles. The attraction between molecules is especially noticeable when they are close to each other. The most striking example is that two drops of water merge into one upon contact.

Electric charge

In the atom of any substance, the number of electrons revolving around the nucleus is equal to the number of protons contained in the nucleus. The electric charge of an electron and a proton are equal in magnitude, which means that the negative charge of the electrons is equal to the positive charge of the nucleus. These charges mutually balance each other, and the atom remains neutral. In an atom, electrons create an electron shell around the nucleus. The electron shell and the nucleus of an atom are in continuous oscillatory motion. When the atoms move, they collide with each other and one or more electrons fly out of them. The atom ceases to be neutral and becomes positively charged. Since its positive charge has become more negative (weak connection between the electron and the nucleus - metal and coal). In other bodies (wood and glass), the electronic shells are not broken. After breaking away from atoms, free electrons move randomly and can be captured by other atoms. The process of appearances and disappearances in the body is continuous. As the temperature increases, the speed of the vibrational movement of atoms increases, the collisions become more frequent, become stronger, the number of free electrons increases. However, the body remains electrically neutral, since the number of electrons and protons in the body does not change. If a certain amount of free electrons is removed from the body, then the positive charge becomes greater than the total charge. The body will be positively charged and vice versa. If a lack of electrons is created in the body, then it is additionally charged. If the excess is negative. The greater this deficiency or excess, the greater the electric charge. In the first case (more positively charged particles), bodies are called conductors (metals, aqueous solutions of salts and acids), and in the second (lack of electrons, negatively charged particles) dielectrics or insulators (amber, quartz, ebonite). For the continuous existence of an electric current, it is necessary to constantly maintain a potential difference in the conductor.

Well, that's a little physics course is over. I think you, with my help, remembered the school curriculum for the 7th grade, and we will analyze what the potential difference is in my next article. Until we meet again on the pages of the site.

Content:

Every layman is familiar with electrical quantities - current, voltage - the operation of household appliances depends on them, but few people have a complete understanding of the definition of electric current. It is significant to compare the electric current with the flow of the river, only in it particles with a charge move, and in the river - water. It must be understood that the current moves in only one direction, conditions must be created for its existence, we will consider these processes in more detail.

Basic definitions

Electricity surrounds us every day, but not every person understands what an electric current and the quantities associated with it are, but they are important for Everyday life. There are several interpretations of the concept of electric current:

1. The definition accepted in a school textbook that an electric current is the movement of particles that have a charge due to the action of an electric field on them. Particles are: protons, holes, electrons, ions.
2. In the electrical literature of higher educational institutions It is written that electric current is the rate at which charge changes over time. The negative charge of electrons is assumed, positive for protons and neutral for neutrons.

In electrical engineering, experts note the importance of such a concept as current strength - this is the number of particles that have a charge that pass through the cross section of a conductor over time. The movement of current in a conductor can be described as follows: “... All conductive materials have an internal structure (molecules, atoms, nuclei with rotating electrons), when a chemical reaction affects the material, electrons from one atom run to another. A situation is created in which some atoms lack electrons, while others experience an excess of them, which shows the opposite charge. Electrons tend to move from one substance to another, this movement is the electric current.

Specialists focus on the fact that in this case the current flows only until the moment when the charges in the two substances are equalized.

To understand the movement of current, it is important to know the definition of voltage - this is the potential difference that is taken at two points in the electric field, measured in volts.

Electric Energy

In different regions, in particular, in Ukraine, a simple man in the street is interested in: “What is an electric strum?”, for what purpose it is used, what it comes from. Everyday we use electrical energy, which is represented by alternating current in electrical networks.

An alternating current in a conductor is when particles that have a charge over a certain period of time change it in direction, as well as in magnitude. Graphically, alternating current is represented by a sinusoid. It is created by generators in which coils with wires rotate and, in the process of rotation, cross the magnetic field. During the period of rotation, the coils can open and close in relation to the magnetic field, which creates an electric current that changes direction in the conductors, and a full cycle takes place in one minute.

The rotation of the generators comes from steam turbines having different sources supply: coal, gas, nuclear reactor, oil. Further, through the system of transformers, the voltage rises, through the conductors of the desired diameter, it is transferred without loss for a long distance. The diameter of the wire through which the current flows determines its strength and magnitude, hot lines in the energy industry are called main power transmission lines, there are also grounded options when electricity is transmitted underground.

Where is electricity applied?

It is the current that makes life much easier for us, creating comfort in the house. It is used for lighting rooms, streets, for drying things, in heating elements of electric stoves, in other household appliances and devices, performs the work of lifting garage doors, etc.

Conditions necessary to receive electricity

For the existence of an electric current, the following conditions are necessary: ​​the presence of particles with a charge, an electrically conductive material along which the particles will move, and a voltage source. An important condition for obtaining electric current is the presence of voltage, which is determined by the potential difference. In other words, the force created by the charged particles of repulsion is greater at one point than at another.

There are no natural sources of voltage, for this reason electrons are evenly distributed around us, but inventions such as batteries made it possible to accumulate electrical energy in them.

Another important condition is the electrical resistance, or conductor, along which the charged particles will move. Materials in which this action is possible are called electrically conductive, and those in which there is no free movement of electrons are called insulators. An ordinary wire has a conductive metal core and an insulating sheath.

Electric current in conductors

In any conductor there are carriers of electric charge, which are set in motion under the influence of the force of the field created by the electric machine.

Metal conductors carry charge with the help of electrons. The higher the temperature of the conductor and the heating of the wire, the worse the current flows, since the chaotic movement of atoms begins in it from thermal exposure, and the resistance of the conductive material increases. The lower the temperature of the conductor (ideally, tending to zero), the lower its resistance.

Liquids can conduct electricity using ions (electrolytes). The movement occurs to the electrode, which has the opposite sign with the ion, and, settling on it, the ions carry out the electrolysis process. Anions are positively charged ions moving towards the cathode. Cations - ions having a negative charge move towards the anode. In the process of heating the electrolyte, its resistance decreases.

The gas also has conductivity, the electric current in it is plasma. Movement occurs with the help of charged ions or free electrons, which are obtained in the process of radiation.

A cathode ray tube is an example of electric current in a vacuum from a cathode rod to an anode rod.

Electric current in semiconductors

To understand the passage of current in this material, let's give it a definition. Semiconductor - an intermediate material between a conductor and an insulator, depends on the specific conductivity, the presence of impurities in it, the temperature state and the radiation acting on it. The lower the temperature, the greater the resistance of the semiconductor, its properties affect the measurement of characteristics. The electric current in a semiconductor is the sum of the electron and hole currents.

When the temperature of a semiconductor rises, covalent bonds are broken due to the action of thermal energy on valence electrons, free electrons are formed, and a hole is obtained at the break point. It is engaged in the valence electron of another pair, and itself moves further in the crystal. When a free electron meets a hole, recombination occurs between them, the restoration of electronic bonds. When a semiconductor is exposed to the energy of electromagnetic radiation, electron-hole pairs appear in it.

Electric current laws

In electrical engineering, the basic laws that define the electric current are applied. One of the most important is Ohm's law, a feature of which is the speed of energy transfer without changing its shape from one point to another.

This law shows the relationship between voltage and current strength, as well as the resistance of a conductor or circuit section. Resistance is measured in ohms.

The work of an electric current is determined by the Joule-Lenz law, which says that at any point in the circuit, the current does work.

Faraday discovered magnetic induction, and also experimentally established that when the line of magnetic induction crosses the surface of a closed conductor, an electric current appears in it. He derived the law of electromagnetic induction:

Non-closed conductors crossing the lines of the magnetic field receive voltage at the ends, which indicates the appearance of an EMF of induction. If the magnetic flux is unchanged and crosses a closed circuit, then no electric current arises in it. The EMF of induction of a closed circuit, when the magnetic flux changes, is equal to the modulus of its rate of change.

Output

When an electric current flows through the conductor, it heats it up, for this reason it is necessary to observe safety measures when working with electrical appliances and devices. The power transmission line must not be overloaded, it may become hot and cause a fire. Electric current always follows the path of least resistance.

At the time of occurrence of short circuit ( short circuit) the current increases many times, there is an instantaneous release of a huge thermal value, which melts the metal. Electric current can cause burns on the body of a person or animal, but is used in intensive care units, for depressive solutions and the treatment of diseases.

According to the rules of electrical safety, a current perceptible by a person comes from a value of one milliampere, and a current with 0.01 amperes is considered hazardous to health, a current of 0.1 amperes is defined as a lethal value. Safe voltage for humans is 12-24-32-42 volts.

The first discoveries related to the work of electricity began in the 7th century BC. Philosopher Ancient Greece Thales of Miletus revealed that when amber is rubbed against wool, it is subsequently able to attract lightweight objects. From Greek "electricity" is translated as "amber". In 1820, André-Marie Ampère established the law of direct current. In the future, the magnitude of the current, or what the electric current is measured in, began to be denoted in amperes.

Term meaning

The concept of electric current can be found in any physics textbook. electric current- this is an ordered movement of electrically charged particles in a direction. To understand to a simple layman what an electric current is, you should use the dictionary of an electrician. In it, the term stands for the movement of electrons through a conductor or ions through an electrolyte.

Depending on the movement of electrons or ions inside the conductor, the following are distinguished: types of currents:

• constant;
• variable;
• intermittent or pulsating.

Basic measurements

The strength of the electric current- the main indicator used by electricians in their work. The strength of the electric current depends on the magnitude of the charge that flows through the electrical circuit for a set period of time. The more electrons flowed from one beginning of the source to the end, the greater will be the charge transferred by the electrons.

A quantity that is measured as the ratio of the electric charge flowing through the cross section of particles in a conductor to the time it passes. Charge is measured in coulombs, time is measured in seconds, and one unit of electricity flow is determined by the ratio of charge to time (coulomb to second) or amperes. The determination of the electric current (its strength) occurs by connecting two terminals in series to the electrical circuit.

When the electric current is working, the movement of charged particles is carried out with the help of an electric field and depends on the strength of the movement of electrons. The value on which the work of the electric current depends is called voltage and is determined by the ratio of the work of the current in a particular part of the circuit and the charge passing through the same part. The volt unit is measured with a voltmeter when the two terminals of the instrument are connected in parallel to the circuit.

The value of electrical resistance is directly dependent on the type of conductor used, its length and cross section. It is measured in ohms.

Power is determined by the ratio of the work of the movement of currents to the time when this work occurred. Measure power in watts.

Such a physical quantity as capacitance is determined by the ratio of the charge of one conductor to the potential difference between the same conductor and the neighboring one. The lower the voltage when the conductors receive an electric charge, the greater their capacitance. It is measured in farads.

The value of the work of electricity at a certain interval of the chain is found using the product of the current strength, voltage and the time period at which the work was carried out. The latter is measured in joules. The determination of the work of the electric current occurs with the help of a meter that connects the readings of all quantities, namely voltage, force and time.

Electrical safety engineering

Knowing the rules of electrical safety will help prevent an emergency and protect human health and life. Since electricity tends to heat the conductor, there is always the possibility of a situation dangerous to health and life. For home security must adhere following simple but important rules:

1. Network insulation must always be in good working order to avoid overloads or the possibility of short circuits.
2. Moisture should not get on electrical appliances, wires, shields, etc. Also, a humid environment provokes short circuits.
3. Be sure to make grounding for all electrical devices.
4. It is necessary to avoid overloading the electrical wiring, as there is a risk of ignition of the wires.

Safety precautions when working with electricity involves the use of rubberized gloves, mittens, rugs, discharge devices, grounding devices for work areas, circuit breakers or fuses with thermal and current protection.

Experienced electricians, when there is a possibility of electric shock, work with one hand, and the other is in their pocket. Thus, the hand-to-hand circuit is interrupted in case of involuntary contact with the shield or other grounded equipment. In case of ignition of equipment connected to the network, extinguish the fire exclusively with powder or carbon dioxide extinguishers.

Application of electric current

Electric current has many properties that allow it to be used in almost all areas. human activity. Ways to use electric current:

Electricity is the most environmentally friendly form of energy today. In the conditions of the modern economy, the development of the electric power industry has planetary significance. In the future, if there is a shortage of raw materials, electricity will take a leading position as an inexhaustible source of energy.

Electric current is an ordered flow of negatively charged elementary particles - electrons. Electricity necessary for lighting houses and streets, ensuring the operability of household and industrial equipment, the movement of urban and main electric transport, etc.

Electricity

• R n - load resistance
• A - indicator
• K - circuit switch

Current- the number of charges passing per unit time through the cross section of the conductor.

• I - current strength
• q is the amount of electricity
• t - time

The unit of current is called ampere A, after the name of the French scientist Ampere.

1A = 10 3 mA = 10 6 uA

Electric current density

electric current a number of physical characteristics are inherent, having quantitative values ​​expressed in certain units. The main physical characteristics of the electric current are its strength and power. Current strength quantified in amperes, and the power of the current - in watts. An equally important physical quantity is the vector characteristic of the electric current, or current density. In particular, the concept of current density is used in the design of power lines.

• J - electric current density A / MM 2
• S - cross-sectional area
• I - current

Direct and alternating current

All electrical devices are powered by permanent or alternating current.

Electricity, whose direction and value do not change, is called permanent.

Electricity, the direction and value of which can change is called variables.

The power supply of many electrical devices is carried out alternating current, the change of which is graphically represented as a sinusoid.

Use of electric current

It can be stated with certainty that the greatest achievement of mankind is the discovery electric current and its use. From electric current heat and light in houses depend, the flow of information from outside world, communication of people located in different parts of the planet, and much more.

Modern life is unimaginable without the widespread availability of electricity. Electricity is present in absolutely all spheres of human activity: in industry and agriculture, in science and space.

Electricity It is also an integral part of everyday life. This ubiquitous distribution of electricity was made possible by its unique properties. Electrical energy can be instantly transmitted over vast distances and converted into different kinds energies of a different genesis.

The main consumers of electrical energy are industrial and industrial sectors. With the help of electricity, various mechanisms and devices are put into action, multi-stage technological processes are carried out.

It is impossible to overestimate the role of electricity in ensuring the operation of transport. Railway transport is almost completely electrified. The electrification of railway transport has played a significant role in ensuring the capacity of roads, increasing the speed of movement, reducing the cost of passenger transportation, and solving the problem of fuel economy.

The presence of electricity is an indispensable condition for ensuring comfortable living conditions for people. All Appliances: TVs, washing machines, microwave ovens, heating appliances - has found its place in human life only thanks to the development of electrical production.

The leading role of electricity in the development of civilization is undeniable. There is no such area in the life of mankind that would do without the consumption of electrical energy and the alternative of which could be muscular strength.