Basic concepts of electric current. Determination of electric current

When a person learned to create and use electric current, his quality of life increased dramatically. Now the importance of electricity continues to increase every year. In order to learn to understand more complex issues related to electricity, you must first understand what electric current is.

What is current

The definition of electric current is its representation in the form of a directed flow of moving carrier particles, positively or negatively charged. Charge carriers can be:

electrons charged with a minus sign moving in metals;
ions in liquids or gases;
positively charged holes from moving electrons in semiconductors.

What current is is also determined by the presence of an electric field. Without it, a directed flow of charged particles will not arise.

The concept of electric currentIt would be incomplete without listing its manifestations:

Any electric current is accompanied by a magnetic field;
The conductors heat up as it passes;
Electrolytes change the chemical composition.

Conductors and semiconductors

Electric current can only exist in a conducting medium, but the nature of its flow is different:

Metal conductors contain free electrons that begin to move under the influence of an electric field. When the temperature increases, the resistance of the conductors also increases, since heat increases the movement of atoms in a chaotic order, which interferes with free electrons;
In a liquid medium formed by electrolytes, the resulting electric field causes a process of dissociation - the formation of cations and anions, which move towards the positive and negative poles (electrodes) depending on the sign of the charge. Heating the electrolyte leads to a decrease in resistance due to more active decomposition of molecules;

Important! The electrolyte may be solid, but the nature of the current flow in it is identical to liquid.

The gaseous medium is also characterized by the presence of ions that come into motion. Plasma is formed. Radiation also produces free electrons that participate in directed motion;
When an electric current is created in a vacuum, the electrons released at the negative electrode move towards the positive electrode;
In semiconductors, there are free electrons that break bonds when heated. In their places there remain holes with a charge with a “plus” sign. Holes and electrons are capable of creating directed motion.

Non-conducting media are called dielectric.

Important! The direction of the current corresponds to the direction of movement of charge carrier particles with a plus sign.

Type of current

Constant. It is characterized by a constant quantitative value of the current and direction;
Variable. Over time, it periodically changes its characteristics. It is divided into several varieties, depending on the parameter being changed. Mainly the quantitative value of the current and its direction vary along a sinusoid;
Eddy currents. Occur when the magnetic flux undergoes changes. Form closed circuits without moving between poles. Eddy currents cause intense heat generation, and as a result, losses increase. In the cores of electromagnetic coils, they are limited by using a design of individual insulated plates instead of a solid one.

Electrical characteristics

Current strength. This is a quantitative measurement of the charge passing per unit of time across a cross-section of conductors. Charges are measured in coulombs (C), the time unit is second. Current strength is C/s. The resulting ratio was called ampere (A), which measures the quantitative value of the current. The measuring device is an ammeter, connected in series to the electrical connection circuit;
Power. The electric current in the conductor must overcome the resistance of the medium. The work expended to overcome it over a certain period of time will be power. In this case, electricity is converted into other types of energy - work is done. Power depends on current and voltage. Their product will determine the active power. When multiplied by time, the energy consumption is obtained - what the meter shows. Power can be measured in volt-amperes (VA, kVA, mVA) or in watts (W, kW, mW);
Voltage. One of the three most important characteristics. For current to flow, it is necessary to create a potential difference between two points in a closed circuit of electrical connections. Voltage is characterized by the work done by an electric field when a single charge carrier moves. According to the formula, the unit of voltage is J/C, which corresponds to a volt (V). The measuring device is a voltmeter, connected in parallel;
Resistance. Characterizes the ability of conductors to pass electric current. Determined by the conductor material, length and cross-sectional area. Measurement is in ohms (Ohm).

Laws for electric current

Electrical circuits are calculated using three main laws:

Ohm's law. It was studied and formulated by a physicist from Germany at the beginning of the 19th century for direct current, then it was also applied to alternating current. It establishes the relationship between current, voltage and resistance. Almost any electrical circuit is calculated based on Ohm's law. Basic formula: I = U/R, or current is directly proportional to voltage and inversely proportional to resistance;

Faraday's law. Refers to electromagnetic induction. The appearance of inductive currents in conductors is caused by the influence of a magnetic flux that changes over time due to the induction of EMF (electromotive force) in a closed loop. The magnitude of the induced emf, measured in volts, is proportional to the rate at which the magnetic flux changes. Thanks to the law of induction, generators produce electricity;
Joule-Lenz law. It is important when calculating the heating of conductors, which is used for the design and manufacture of heating, lighting devices, and other electrical equipment. The law allows us to determine the amount of heat released during the passage of electric current:

where I is the strength of the flowing current, R is the resistance, t is time.

Electricity in the atmosphere

An electric field may exist in the atmosphere, and ionization processes occur. Although the nature of their occurrence is not completely clear, there are various explanatory hypotheses. The most popular is a capacitor, as an analogue for representing electricity in the atmosphere. Its plates can be used to represent the earth's surface and the ionosphere, between which a dielectric - air - circulates.

Types of atmospheric electricity:

Lightning discharges. Lightning with a visible glow and thunderclaps. Lightning voltage reaches hundreds of millions of volts at a current of 500,000 A;

St. Elmo's Fire. Corona discharge of electricity formed around wires, masts;
Ball lightning. A ball-shaped discharge moving through the air;
Polar Lights. Multicolor glow of the earth's ionosphere under the influence of charged particles penetrating from space.

Humans use the beneficial properties of electric current in all areas of life:

lighting;
signal transmission: telephone, radio, television, telegraph;
electric transport: trains, electric cars, trams, trolleybuses;
creating a comfortable microclimate: heating and air conditioning;
Medical equipment;
household use: electrical appliances;
computers and mobile devices;
industry: machines and equipment;
electrolysis: production of aluminum, zinc, magnesium and other substances.

Electrical Hazard

Direct contact with electric current without protective equipment is deadly to humans. Several types of impacts are possible:

thermal burn;
electrolytic breakdown of blood and lymph with a change in its composition;
convulsive muscle contractions can provoke cardiac fibrillation until it stops completely, and disrupt the functioning of the respiratory system.

Important! The current felt by a person begins with a value of 1 mA; if the current value is 25 mA, serious negative changes in the body are possible.

The most important characteristic of electric current is that it can do useful work for a person: light a house, wash and dry clothes, cook dinner, heat a home. Nowadays, its use in information transmission occupies a significant place, although this does not require a lot of energy consumption.

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Electric current is now used in every building, knowing current characteristics in the electrical network at home, you should always remember that it is dangerous to life.

Electric current is the effect of the directional movement of electric charges (in gases - ions and electrons, in metals - electrons), under the influence of an electric field.

The movement of positive charges along the field is equivalent to the movement of negative charges against the field.

Usually the direction of the electric charge is taken to be the direction of the positive charge.

current power;
voltage;
current strength;
current resistance.

Current power.

Electric current power is called the ratio of the work performed by the current to the time during which this work was performed.

The power that an electric current develops in a section of a circuit is directly proportional to the magnitude of the current and voltage in that section. Power (electric and mechanical) measured in Watts (W).

Current power does not depend on the time of the pro-te-ka-niya of the electric current in the circuit, but is defined as the pro-from-ve-de voltage on current strength.

Voltage.

Electric voltage is a quantity that shows how much work is done by the electric field when moving a charge from one point to another. The voltage in different parts of the circuit will be different.

Eg: the voltage on a section of an empty wire will be very small, and the voltage on a section with any load will be much higher, and the magnitude of the voltage will depend on the amount of work done by the current. Voltage is measured in volts (1 V). To determine the voltage there is a formula: U=A/q, where

U - voltage,
A is the work done by the current to move charge q to a certain section of the circuit.

Current strength.

Current strength refers to the number of charged particles that flow through the cross section of a conductor.

A-priory current strength directly proportional to voltage and inversely proportional to resistance.

Electric current strength measured by an instrument called an Ammeter. The amount of electric current (the amount of charge transferred) is measured in amperes. To increase the range of unit of change designations, there are multiplicity prefixes such as micro - microampere (μA), miles - milliampere (mA). Other consoles are not used in everyday use. For example: they say and write “ten thousand amperes”, but they never say or write 10 kiloamperes. Such meanings are not used in everyday life. The same can be said about nanoamps. Usually they say and write 1×10-9 Amperes.

Current resistance.

Electrical resistance is a physical quantity that characterizes the properties of a conductor that prevent the passage of electric current and is equal to the ratio of the voltage at the ends of the conductor to the strength of the current flowing through it.

Resistance for alternating current circuits and for alternating electromagnetic fields is described by the concepts of impedance and characteristic impedance. Current resistance(often denoted by the letter R or r) the current resistance is considered, within certain limits, to be a constant value for a given conductor. Under electrical resistance understand the ratio of the voltage at the ends of a conductor to the current flowing through the conductor.

Conditions for the occurrence of electric current in a conducting medium:

1) the presence of free charged particles;

2) if there is an electric field (there is a potential difference between two points of the conductor).

Types of effects of electric current on conductive material.

1) chemical - a change in the chemical composition of conductors (occurs mainly in electrolytes);

2) thermal - the material through which the current flows is heated (this effect is absent in superconductors);

3) magnetic - the appearance of a magnetic field (occurs in all conductors).

Main characteristics of current.

1. The current strength is denoted by the letter I - it is equal to the amount of electricity Q passing through the conductor during time t.

I=Q/t

The current strength is determined by an ammeter.

The voltage is determined by a voltmeter.

3. Resistance R of the conductive material.

Resistance depends:

a) on the cross-section of the conductor S, on its length l and material (denoted by the resistivity of the conductor ρ);

R=pl/S

b) on temperature t°C (or T): R = R0 (1 + αt),

where R0 is the conductor resistance at 0°C,
α - temperature coefficient of resistance;

c) to obtain various effects, conductors can be connected both in parallel and in series.

Current characteristics table.

Compound

Sequential

Parallel

Conservation value

I 1 = I 2 = … = I n I = const

U 1 = U 2 = …U n U = const

Sum value

voltage

e=Ast/q

The value equal to the work expended by external forces to move a positive charge along the entire circuit, including the current source, to the charge is called the electromotive force of the current source (EMF):

e=Ast/q

Current characteristics must be known when repairing electrical equipment.

First of all, it is worth finding out what electric current is. Electric current is the ordered movement of charged particles in a conductor. For it to arise, an electric field must first be created, under the influence of which the above-mentioned charged particles will begin to move.

The first knowledge of electricity, many centuries ago, related to electrical “charges” produced through friction. Already in ancient times, people knew that amber, rubbed with wool, acquired the ability to attract light objects. But only at the end of the 16th century, the English physician Gilbert studied this phenomenon in detail and found out that many other substances had exactly the same properties. Bodies that, like amber, after rubbing, can attract light objects, he called electrified. This word is derived from the Greek electron - “amber”. Currently, we say that bodies in this state have electrical charges, and the bodies themselves are called “charged.”

Electric charges always arise when different substances come into close contact. If the bodies are solid, then their close contact is prevented by microscopic protrusions and irregularities that are present on their surface. By squeezing such bodies and rubbing them against each other, we bring together their surfaces, which without pressure would only touch at a few points. In some bodies, electrical charges can move freely between different parts, but in others this is impossible. In the first case, the bodies are called “conductors”, and in the second - “dielectrics, or insulators”. Conductors are all metals, aqueous solutions of salts and acids, etc. Examples of insulators are amber, quartz, ebonite and all gases found under normal conditions.

Nevertheless, it should be noted that the division of bodies into conductors and dielectrics is very arbitrary. All substances conduct electricity to a greater or lesser extent. Electric charges are positive and negative. This kind of current will not last long, because the electrified body will run out of charge. For the continued existence of an electric current in a conductor, it is necessary to maintain an electric field. For these purposes, electric current sources are used. The simplest case of the occurrence of electric current is when one end of the wire is connected to an electrified body, and the other to the ground.

Electrical circuits supplying current to light bulbs and electric motors did not appear until the invention of batteries, which dates back to around 1800. After this, the development of the doctrine of electricity went so quickly that in less than a century it became not just a part of physics, but formed the basis of a new electrical civilization.

Basic quantities of electric current

Amount of electricity and current. The effects of electric current can be strong or weak. The strength of the electric current depends on the amount of charge that flows through the circuit in a certain unit of time. The more electrons moved from one pole of the source to the other, the greater the total charge transferred by the electrons. This net charge is called the amount of electricity passing through a conductor.

In particular, the chemical effect of electric current depends on the amount of electricity, i.e., the greater the charge passed through the electrolyte solution, the more substance will be deposited on the cathode and anode. In this regard, the amount of electricity can be calculated by weighing the mass of the substance deposited on the electrode and knowing the mass and charge of one ion of this substance.

Current strength is a quantity that is equal to the ratio of the electric charge passing through the cross section of the conductor to the time of its flow. The unit of charge is the coulomb (C), time is measured in seconds (s). In this case, the unit of current is expressed in C/s. This unit is called ampere (A). In order to measure the current in a circuit, an electrical measuring device called an ammeter is used. For inclusion in the circuit, the ammeter is equipped with two terminals. It is connected in series to the circuit.

Electrical voltage. We already know that electric current is the ordered movement of charged particles - electrons. This movement is created using an electric field, which does a certain amount of work. This phenomenon is called the work of electric current. In order to move more charge through an electrical circuit in 1 s, the electric field must do more work. Based on this, it turns out that the work of electric current should depend on the strength of the current. But there is one more value on which the work of the current depends. This quantity is called voltage.

Voltage is the ratio of the work done by the current in a certain section of an electrical circuit to the charge flowing through the same section of the circuit. Current work is measured in joules (J), charge - in coulombs (C). In this regard, the unit of measurement for voltage will become 1 J/C. This unit was called the volt (V).

In order for voltage to arise in an electrical circuit, a current source is needed. When the circuit is open, voltage is present only at the terminals of the current source. If this current source is included in the circuit, voltage will also arise in individual sections of the circuit. In this regard, a current will appear in the circuit. That is, we can briefly say the following: if there is no voltage in the circuit, there is no current. In order to measure voltage, an electrical measuring instrument called a voltmeter is used. In its appearance, it resembles the previously mentioned ammeter, with the only difference being that the letter V is written on the voltmeter scale (instead of A on the ammeter). The voltmeter has two terminals, with the help of which it is connected in parallel to the electrical circuit.

Electrical resistance. After connecting various conductors and an ammeter to the electrical circuit, you can notice that when using different conductors, the ammeter gives different readings, i.e. in this case, the current strength available in the electrical circuit is different. This phenomenon can be explained by the fact that different conductors have different electrical resistance, which is a physical quantity. It was named Ohm in honor of the German physicist. As a rule, larger units are used in physics: kilo-ohm, mega-ohm, etc. The resistance of a conductor is usually denoted by the letter R, the length of the conductor is L, and the cross-sectional area is S. In this case, the resistance can be written as a formula:

R = r * L/S

where the coefficient p is called resistivity. This coefficient expresses the resistance of a conductor 1 m long with a cross-sectional area equal to 1 m2. Specific resistance is expressed in Ohms x m. Since wires, as a rule, have a rather small cross-section, their areas are usually expressed in square millimeters. In this case, the unit of resistivity will be Ohm x mm2/m. In the table below. 1 shows the resistivities of some materials.

*Table 1. Electrical resistivity of some materials*
Material	p, Ohm x m2/m	Material	p, Ohm x m2/m
Copper	0,017	Platinum-iridium alloy	0,25
Gold	0,024	Graphite	13
Brass	0,071	Coal	40
Tin	0,12	Porcelain	1019
Lead	0,21	Ebonite	1020
Metal or alloy
Silver	0,016	Manganin (alloy)	0,43
Aluminum	0,028	Constantan (alloy)	0,50
Tungsten	0,055	Mercury	0,96
Iron	0,1	Nichrome (alloy)	1,1
Nickelin (alloy)	0,40	Fechral (alloy)	1,3
Nickelin (alloy)	0,40	Chromel (alloy)	1,5

According to the table. 1 it becomes clear that copper has the lowest electrical resistivity, and metal alloy has the highest. In addition, dielectrics (insulators) have high resistivity.

Electrical capacity. We already know that two conductors isolated from each other can accumulate electrical charges. This phenomenon is characterized by a physical quantity called electrical capacitance. The electrical capacitance of two conductors is nothing more than the ratio of the charge of one of them to the potential difference between this conductor and the neighboring one. The lower the voltage when the conductors receive a charge, the greater their capacity. The unit of electrical capacitance is the farad (F). In practice, fractions of this unit are used: microfarad (μF) and picofarad (pF).

If you take two conductors isolated from each other and place them at a short distance from one another, you will get a capacitor. The capacitance of a capacitor depends on the thickness of its plates and the thickness of the dielectric and its permeability. By reducing the thickness of the dielectric between the plates of the capacitor, the capacitance of the latter can be significantly increased. On all capacitors, in addition to their capacity, the voltage for which these devices are designed must be indicated.

Work and power of electric current. From the above it is clear that electric current does some work. When connecting electric motors, the electric current makes all kinds of equipment work, moves trains along the rails, illuminates the streets, heats the home, and also produces a chemical effect, i.e., allows electrolysis, etc. We can say that the work done by the current on a certain section of the circuit is equal to the product current, voltage and time during which the work was performed. Work is measured in joules, voltage in volts, current in amperes, time in seconds. In this regard, 1 J = 1B x 1A x 1s. From this it turns out that in order to measure the work of electric current, three instruments should be used at once: an ammeter, a voltmeter and a clock. But this is cumbersome and ineffective. Therefore, usually, the work of electric current is measured with electric meters. This device contains all of the above devices.

The power of the electric current is equal to the ratio of the work of the current to the time during which it was performed. Power is designated by the letter “P” and is expressed in watts (W). In practice, kilowatts, megawatts, hectowatts, etc. are used. In order to measure the power of the circuit, you need to take a wattmeter. Electrical engineers express the work of current in kilowatt-hours (kWh).

Basic laws of electric current

Ohm's law. Voltage and current are considered the most useful characteristics of electrical circuits. One of the main features of the use of electricity is the rapid transportation of energy from one place to another and its transfer to the consumer in the required form. The product of the potential difference and the current gives power, i.e., the amount of energy given off in the circuit per unit time. As mentioned above, to measure the power in an electrical circuit, 3 devices would be needed. Is it possible to get by with just one and calculate the power from its readings and some characteristic of the circuit, such as its resistance? Many people liked this idea and found it fruitful.

So what is the resistance of a wire or circuit as a whole? Does a wire, like water pipes or vacuum system pipes, have a permanent property that could be called resistance? For example, in pipes, the ratio of the pressure difference producing flow divided by the flow rate is usually a constant characteristic of the pipe. Similarly, heat flow in a wire is governed by a simple relationship involving the temperature difference, the cross-sectional area of the wire, and its length. The discovery of such a relationship for electrical circuits was the result of a successful search.

In the 1820s, the German schoolteacher Georg Ohm was the first to begin searching for the above relationship. First of all, he strived for fame and fame, which would allow him to teach at the university. That is why he chose an area of research that promised special advantages.

Om was the son of a mechanic, so he knew how to draw metal wire of different thicknesses, which he needed for experiments. Since it was impossible to buy suitable wire in those days, Om made it himself. During his experiments, he tried different lengths, different thicknesses, different metals and even different temperatures. He varied all these factors one by one. In Ohm's time, batteries were still weak and produced inconsistent current. In this regard, the researcher used a thermocouple as a generator, the hot junction of which was placed in a flame. In addition, he used a crude magnetic ammeter, and measured potential differences (Ohm called them “voltages”) by changing the temperature or the number of thermal junctions.

The study of electrical circuits has just begun to develop. After batteries were invented around 1800, it began to develop much faster. Various devices were designed and manufactured (quite often by hand), new laws were discovered, concepts and terms appeared, etc. All this led to a deeper understanding of electrical phenomena and factors.

Updating knowledge about electricity, on the one hand, became the reason for the emergence of a new field of physics, on the other hand, it was the basis for the rapid development of electrical engineering, i.e. batteries, generators, power supply systems for lighting and electric drive, electric furnaces, electric motors, etc. were invented , other.

Ohm's discoveries were of great importance both for the development of the study of electricity and for the development of applied electrical engineering. They made it possible to easily predict the properties of electrical circuits for direct current, and subsequently for alternating current. In 1826, Ohm published a book in which he outlined theoretical conclusions and experimental results. But his hopes were not justified; the book was greeted with ridicule. This happened because the method of crude experimentation seemed unattractive in an era when many were interested in philosophy.

He had no choice but to leave his teaching position. He did not achieve an appointment to the university for the same reason. For 6 years, the scientist lived in poverty, without confidence in the future, experiencing a feeling of bitter disappointment.

But gradually his works gained fame, first outside Germany. Om was respected abroad and benefited from his research. In this regard, his compatriots were forced to recognize him in his homeland. In 1849 he received a professorship at the University of Munich.

Ohm discovered a simple law establishing the relationship between current and voltage for a piece of wire (for part of a circuit, for the entire circuit). In addition, he compiled rules that allow you to determine what will change if you take a wire of a different size. Ohm's law is formulated as follows: the current strength in a section of a circuit is directly proportional to the voltage in this section and inversely proportional to the resistance of the section.

Joule-Lenz law. Electric current in any part of the circuit does some work. For example, let's take any section of the circuit between the ends of which there is a voltage (U). By definition of electric voltage, the work done when moving a unit of charge between two points is equal to U. If the current strength in a given section of the circuit is equal to i, then in time t the charge it will pass, and therefore the work of the electric current in this section will be:

A = Uit

This expression is valid for direct current in any case, for any section of the circuit, which may contain conductors, electric motors, etc. The current power, i.e. work per unit time, is equal to:

Р = A/t = Ui

This formula is used in the SI system to determine the unit of voltage.

Let us assume that the section of the circuit is a stationary conductor. In this case, all the work will turn into heat, which will be released in this conductor. If the conductor is homogeneous and obeys Ohm’s law (this includes all metals and electrolytes), then:

U = ir

where r is the conductor resistance. In this case:

A = rt2i

This law was first experimentally deduced by E. Lenz and, independently of him, by Joule.

It should be noted that heating conductors has numerous applications in technology. The most common and important among them are incandescent lighting lamps.

Law of Electromagnetic Induction. In the first half of the 19th century, the English physicist M. Faraday discovered the phenomenon of magnetic induction. This fact, having become the property of many researchers, gave a powerful impetus to the development of electrical and radio engineering.

In the course of experiments, Faraday found out that when the number of magnetic induction lines penetrating a surface bounded by a closed loop changes, an electric current arises in it. This is the basis of perhaps the most important law of physics - the law of electromagnetic induction. The current that occurs in the circuit is called induction. Due to the fact that an electric current arises in a circuit only when free charges are exposed to external forces, then with a changing magnetic flux passing along the surface of a closed circuit, these same external forces appear in it. The action of external forces in physics is called electromotive force or induced emf.

Electromagnetic induction also appears in open conductors. When a conductor crosses magnetic lines of force, voltage appears at its ends. The reason for the appearance of such voltage is the induced emf. If the magnetic flux passing through a closed loop does not change, no induced current appears.

Using the concept of “induction emf,” we can talk about the law of electromagnetic induction, i.e., the induction emf in a closed loop is equal in magnitude to the rate of change of the magnetic flux through the surface bounded by the loop.

Lenz's rule. As we already know, an induced current arises in a conductor. Depending on the conditions of its appearance, it has a different direction. On this occasion, the Russian physicist Lenz formulated the following rule: the induced current arising in a closed circuit always has such a direction that the magnetic field it creates does not allow the magnetic flux to change. All this causes the occurrence of an induction current.

Induction current, like any other, has energy. This means that in the event of an induction current, electrical energy appears. According to the law of conservation and transformation of energy, the above-mentioned energy can only arise due to the amount of energy of some other type of energy. Thus, Lenz's rule fully corresponds to the law of conservation and transformation of energy.

In addition to induction, so-called self-induction can appear in the coil. Its essence is as follows. If a current arises in the coil or its strength changes, a changing magnetic field appears. And if the magnetic flux passing through the coil changes, then an electromotive force appears in it, which is called self-induction emf.

According to Lenz's rule, the self-inductive emf when closing a circuit interferes with the current strength and prevents it from increasing. When the circuit is turned off, the self-inductive emf reduces the current strength. In the case when the current strength in the coil reaches a certain value, the magnetic field stops changing and the self-induction emf becomes zero.

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

Meaning of the term

The concept of electric current can be found in any physics textbook. Electric current- this is the ordered movement of electrically charged particles in a direction. To understand to the common man what electric current is, you should use an electrician’s dictionary. 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 a conductor, the following are distinguished: types of currents:

constant;
variable;
periodic or pulsating.

Basic measurement quantities

Electric current strength- the main indicator that electricians use in their work. The strength of the electric current depends on the amount of charge that flows through the electrical circuit over a set period of time. The greater the number of electrons flowing from one beginning of the source to the end, the greater the charge transferred by the electrons will be.

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

When an electric current operates, the movement of charged particles is accomplished using an electric field and depends on the force of electron movement. The value on which the work of an electric current depends is called voltage and is determined by the ratio of the work of the current in a specific part of the circuit and the charge passing through the same part. The unit of measurement volts is measured by a voltmeter when two terminals of the device are connected to a circuit in parallel.

The amount 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 done by the movement of currents to the time when this work occurred. Power is measured in watts.

A physical quantity such 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 conductors receive an electrical charge, the greater their capacity. It is measured in farads.

The amount of work done by electricity at a certain interval in the chain is found using the product of current, voltage and the time period during which the work was carried out. The latter is measured in joules. The operation of electric current is determined using a meter that connects the readings of all quantities, namely voltage, force and time.

Electrical Safety Techniques

Knowledge of electrical safety rules 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. To ensure safety at home must be adhered to the following simple but important rules:

Network insulation must always be in good condition to avoid overloads or the possibility of short circuits.
Moisture should not get on electrical appliances, wires, panels, etc. Also, a humid environment provokes short circuits.
Be sure to ground all electrical devices.
Avoid overloading electrical wiring as there is a risk of the wires catching fire.

Safety precautions when working with electricity involve the use of rubberized gloves, mittens, mats, 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. In this way, the hand-to-hand circuit is interrupted in the event of an involuntary touch to the shield or other grounded equipment. If equipment connected to the network catches fire, 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 of human activity. Ways to use electric current:

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

Today it is difficult to imagine life without such a phenomenon as electricity, but humanity learned to use it for its own purposes not so long ago. The study of the essence and characteristics of this special type of matter took several centuries, but even now we cannot say with confidence that we know absolutely everything about it.

The concept and essence of electric current

Electric current, as is known from school physics courses, is nothing more than the ordered movement of any charged particles. The latter can be either negatively charged electrons or ions. It is believed that this type of matter can only arise in so-called conductors, but this is far from true. The thing is that when any bodies come into contact, a certain number of oppositely charged particles always arise, which can begin to move. In dielectrics, the free movement of the same electrons is very difficult and requires enormous external forces, which is why they say that they do not conduct electric current.

Conditions for the existence of current in the circuit

Scientists have long noticed that this physical phenomenon cannot arise and persist for a long time on its own. The conditions for the existence of electric current include several important provisions. Firstly, this phenomenon is impossible without the presence of free electrons and ions, which act as charge transmitters. Secondly, in order for these elementary particles to begin to move in an orderly manner, it is necessary to create a field, the main feature of which is the potential difference between any points of the electrician. Finally, thirdly, an electric current cannot exist for a long time only under the influence of Coulomb forces, since the potentials will gradually equalize. That is why certain components are needed that are converters of various types of mechanical and thermal energy. They are usually called current sources.

Question about current sources

Electric current sources are special devices that generate an electric field. The most important of them include galvanic cells, solar panels, generators, and batteries. characterized by their power, productivity and operating time.

Current, voltage, resistance

Like any other physical phenomenon, electric current has a number of characteristics. The most important of these include its strength, circuit voltage and resistance. The first of them is a quantitative characteristic of the charge that passes through the cross section of a particular conductor per unit time. Voltage (also called electromotive force) is nothing more than the magnitude of the potential difference due to which a passing charge does a certain amount of work. Finally, resistance is an internal characteristic of a conductor, showing how much force a charge must expend to pass through it.