Work in electricity formula. How is the work of current measured?

The body's ability to produce work is called body energy. Thus, the measure of the amount of energy is work. The energy of a body is greater, the more work this body can produce during its movement. Energy does not disappear, but passes from one form to another. For example, in a generator, mechanical energy is converted into electrical energy, and in an engine, electrical energy is converted into mechanical energy. However, not all energy is useful, i.e. part of it is spent on overcoming the internal resistance of the source and wires.

Job electric current is numerically equal to the product of voltage, current in the circuit and the time it passes. The unit of measurement is Joule.

An electrical measuring instrument is used to measure the work or energy of an electric current − electric energy meter.

Electrical energy, in addition to joules, is measured in watt hours or kilowatt hours:

1 Wh = 3,600 J, 1 kWh = 1,000 Wh.

Electric current power – is the work produced (or consumed) per unit of time. The unit of measurement is Watt.

To measure the power of electric current, an electrical measuring device is used − wattmeter.

The multiple units of power are kilowatt or megawatt:

1 kW = 1,000 W, 1 MW = 1,000,000 W.

In table 1 shows the power of a number of devices.

Table 1

Device name	Device power, kW
Flashlight lamp
Home refrigerator
Lighting lamps (household)
Electric iron
Washing machine
Electric stove	0,6; 0,8; 1; 1,25
Electric vacuum cleaner
Lamps in the stars of the Kremlin towers
Electric locomotive engine VL10
Rolling mill electric motor
Hydrogenerator of the Bratsk hydroelectric power station
Turbogenerator	50 000 − 1 200 000

The relationships between power, current, voltage and resistance are shown in Fig. 1.

P U

I R

R·I

Rice. 1

The rate at which mechanical or other energy is converted into electrical energy at a source is called source power:

Where W And – Electric Energy source.

The rate at which electrical energy is converted in the receiver into other types of energy, in particular thermal energy, is called receiver power:

Power that determines involuntary energy consumption, for example, for heat losses in a source or in conductors, is called power loss:

According to the law of conservation of energy, the power of the source is equal to the sum of the power of consumers and losses:

This expression represents power balance.

The efficiency of energy transfer from source to receiver is characterized by the coefficient of performance (COP) of the source:

Where R 1 or R ist – power supplied by the energy source to the external circuit;

R 2 – power received from outside or power consumed;

∆P or R 0 (R vn ) – power spent to overcome losses in the source or receiver of energy.

Electric current is the directed movement of electrically charged particles. When moving particles collide with molecules and ions of a substance, the kinetic energy of the moving particles is transferred to the ions and molecules, resulting in heating of the conductor. Thus, electrical energy is converted into thermal energy.

In 1844, Russian academician E.H. Lenz and English scientists Joulem simultaneously and independently of each other, a law was discovered that describes the thermal effect of current.

Joule-Lenz law : When an electric current passes through a conductor, the amount of heat generated by the conductor is directly proportional to the square of the current, the resistance of the conductor and the time during which the electric current flows through the conductor:

WhereQ– amount of heat, J,I– current strength, A;R– conductor resistance, Ohm;t– time during which the electric current flowed through the conductor, s.

The Joule-Lenz law is used in calculating the thermal conditions of electricity sources, power lines, consumers and other elements of the electrical circuit. The conversion of electricity into heat is of very great practical importance. At the same time, the thermal effect in many cases turns out to be harmful (Fig. 2).

Electricity meters are installed in each apartment or private house, according to the readings of which the owners pay bills on a monthly basis. Such control devices take into account the number of kilowatt-hours consumed by all electrical appliances and light sources over a certain period of time. Many people wonder what these “kilowatt hours” are. The answer is simple: this is how the work of the current is measured.

Jpg?x15027" alt="External view of the apartment meter, which keeps track of the work performed by the electric current" width="600" height="338" srcset="" data-srcset="https://elquanta.ru/wp-content/uploads/2018/03/1-zaglavnaja-9-600x338..jpg 700w" sizes="(max-width: 600px) 100vw, 600px">!}

Appearance of an apartment meter, which keeps track of the work performed by the electric current

Current work

Every person uses electricity specific goals. Electric current performs a certain work, passing through an electrical circuit, as a result of which electrical appliances, lighting equipment, etc. function.

The work of an electric current is a quantity numerically equal to the product of the strength of the electric current and the voltage at the ends of the circuit section and the time period during which such work was performed. If any of these derivatives changes in one direction or another, then the work done by the current will decrease or increase.

This current characteristic is denoted by the capital Latin letter “A”, and is measured in joules or kilowatt-hours, abbreviated “J” and “kWh”, respectively.

On a note. The work of the current shows how much electricity has been converted into other types of energy (thermal or light) over a specific period. For electricity, the law of conservation of energy is true.

The formula by which the work done by electric current is measured is as follows:

A = U*I*t, where:

• A is a quantitative indicator of the work performed by the current;
• U – electrical voltage in the circuit;
• I – electric current strength;

and, having only data on the strength of the electric current and resistance in the electrical circuit, this value is calculated by the formula:

In this formula, the following quantities are lettered:

• A – work of electric current;
• U – voltage in the circuit;
• R – resistance on the circuit section;
• I – current strength;
• t is the time during which the electric current was operating.

Interesting to know. Meters usually take into account the work of electric current in kWh. This unit is used in practice more often than the generally accepted unit of electrical work, the joule, named after the famous physicist. The fact is that the Joule is a rather small unit, and 1 kWh = 3,600,000 J.

To measure the work of current, devices such as a voltmeter, ammeter, and watch are needed. In practice, measurements are carried out using a prefabricated device - an electricity meter.

Jpg?x15027" alt=" An electrical circuit into which a voltmeter and an ammeter are connected to measure the work of electric current" width="600" height="338" srcset="" data-srcset="https://elquanta.ru/wp-content/uploads/2018/03/2-izmerenie-raboty-600x338..jpg 700w" sizes="(max-width: 600px) 100vw, 600px">!}

An electrical circuit in which a voltmeter and an ammeter are connected to measure the work of an electric current

Current power

Also important is the concept of electric current power, which is directly dependent on the work performed.

The power of the electric current is numerically equal to the ratio of the work done to the time during which this work was done. Electrical power is similar in definition to mechanical power, but is denoted by the letter P.

From the definition of power follows the formula:

P = A/t, where:

• P – electric current power;
• A – work performed by current;
• t is the time during which the electric current was operating.

If you replace the numerator in this formula with U*I*t, you get the following equality:

The unit of measurement for electrical power is the Watt (W). 1 W is equal to a current of 1 A with a voltage of 1 V. Watt– a rather small unit, so in practice additional ones are used:

• kW (kilowatt);
• MW (megawatt);
• GW (gigawatt).

The power of the electric current is experimentally determined using an ammeter and a voltmeter or a special device - a wattmeter.

Jpg?.jpg 600w, https://elquanta.ru/wp-content/uploads/2018/03/3-vattmetr.jpg 700w" sizes="(max-width: 600px) 100vw, 600px">

The work done by an electric current shows how much work was done by the electric field when moving charges along a conductor.

Knowing two formulas:

I = q/t..... And..... U = A/q
You can derive a formula for calculating the work of electric current:

The work of an electric current is equal to the product of the current strength and the voltage and the time the current flows in the circuit.

Unit of measurement of electric current work in the SI system:

[A] = 1 J = 1A.B.c

LEARN IT, IT WILL BE USEFUL

When calculating the work of electric current, it is often used
off-system multiple unit of electric current work: 1 kWh (kilowatt-hour).

INTERESTING

At one time, J. Watt proposed such a unit as “horsepower” as a unit of power. This unit of measurement has survived to this day. But in England in 1882, the British Association of Engineers decided to assign the name of J. Watt to a unit of power. Now the name James Watt can be read on any light bulb.
This was the first time in the history of technology that a unit of measurement was given its own name.
From this incident the tradition of assigning proper names to units of measurement began.

They say that...
A brewer bought one of Watt's steam engines to replace the horse that drove the water pump. When choosing the required power of a steam engine, the brewer defined the horse's labor force as eight hours of non-stop work until the horse was completely exhausted. The calculation showed that every second the horse raised 75 kg of water to a height of 1 meter, which was taken as a unit of power of 1 horsepower.

DO YOU KNOW

The current flowing in the coils of electric lamps heats them to a very high temperature.
Therefore, in order for the spirals to last longer, they are enclosed in glass cylinders filled with high-power lamps with inert gas.

In cylinders of low power lamps (up to 40 W) there is a vacuum. To make the lamp work longer, the temperature of the filament of such lamps is lower, and the light has a yellow tint.

Atmospheric electricity is dangerous because it manifests itself in the form of linear discharges (lightning), which occur on our planet approximately 100 times every second. Atmospheric electric charges can have a voltage of up to 1 billion volts, and the lightning current can reach 200 thousand amperes. The lifetime of lightning is estimated from 0.1 to 1 second.
The temperature reaches 6-10 thousand degrees Celsius.
And if we assume that the electrical energy of one lightning can be 2500 kW/hour, and one family of three people consumes 250 kW/hour of electricity per month, then the energy of one lightning would be enough to satisfy the needs of this family for 10 months.

CAN YOU DECIDE

Two electric lamps, whose power is 40 and 100 W, are designed for the same voltage.
Compare the filament resistances of both lamps.

The room is lit with 40 electric lamps from a flashlight, connected in series and powered from the city network. After one lamp burned out, the remaining 39 were again connected in series and plugged into the network.
When was the room brighter: with 40 or 39 lamps?

Series-connected copper and iron wires of the same length and cross-section are connected to the battery. Which one will release more heat in the same amount of time?

Two conductors of different lengths, but the same cross-section and material, are connected parallel to each other in an electric current circuit. Which one will release more heat?

How to calculate the work done by electric current? We already know that the voltage at the ends of a section of the circuit is numerically equal to the work that is done when an electric charge of 1 C passes through this section. When an electric charge passing through the same area is not 1 C, but, for example, 5 C, the work done will be 5 times greater. Thus, in order to determine the work of electric current on any section of the circuit, it is necessary to multiply the voltage at the ends of this section of the circuit by the electric charge (amount of electricity) passing through it:

where A is work, U is voltage, q is electric charge. The electric charge passing through a section of the circuit can be determined by measuring the strength of the current and the time it passes:

Using this relationship, we obtain a formula for the work of electric current, which is convenient to use in calculations:

The work of an electric current on a section of a circuit is equal to the product of the voltage at the ends of this section by the current strength and the time during which the work was performed.

Work is measured in joules, voltage in volts, current in amperes and time in seconds, so we can write:

1 joule = 1 volt x 1 ampere x 1 second,

1 J = 1 VA s.

It turns out that to measure the work of electric current, three instruments are needed: a voltmeter, an ammeter and a clock. In practice, the work of electric current is measured with special instruments - counters. The design of the meter seems to combine the three devices mentioned above. Electricity meters can now be seen in almost every apartment.

Example. How much work does the electric motor do in 1 hour if the current in the electric motor circuit is 5 A and the voltage at its terminals is 220 V? Engine efficiency 80%.

Let's write down the conditions of the problem and solve it.

Questions

1. What is the electrical voltage across the circuit section?
2. How can we express the work of electric current in this section through voltage and electric charge passing through a section of a circuit?
3. How to express the work of current in terms of voltage, current and time?
4. What instruments measure the work of electric current?

Exercise 34

1. How much work is done by the electric current in the electric motor in 30 minutes if the current in the circuit is 0.5 A and the voltage at the motor terminals is 12 V?
2. The voltage on the spiral of a light bulb from a flashlight is 3.5 V, the resistance of the spiral is 14 Ohms. How much work does the current do in the light bulb in 5 minutes?
3. Two conductors, each with a resistance of 5 ohms, are connected first in series and then in parallel, and in both cases they are connected to a voltage of 4.5 V. In which case will the work done by the current be greater for the same time and by how many times?

When passing through a circuit, an electric current does work, while the electrical energy of the current source is converted into other types of energy (mechanical, thermal, light, etc.). The work of an electric current is mathematically expressed as the product of voltage, current strength and time of action.

Job A electric current on a section of a circuit with electrical resistance R during ∆t is equal to:

A = IU t = I2 R t

Work is measured in watt-seconds, watt-hours or kilowatt-hours. Accepted as a unit of work joule, or watt-second, i.e. work done by a current of 1 ampere at a voltage of 1 volt in 1 second.

Power is the work done by current per unit time.

The power of an electric current is mathematically expressed by the ratio of the work of the current A In time ∆t . for which this work was completed:

Where,

The passage of current through a conductor is always accompanied by at least one of the special phenomena - current actions. There are three known effects of current: chemical, magnetic and thermal.

Work and power of electric current

In every closed circuit, a double transformation of energy necessarily takes place. In a current source, some energy is modified (for example, in a generator - mechanical) into electrical energy, and in a current circuit it is again converted into an equivalent amount of energy of a different type. The measure of the conversion of electricity into any other types of energy in a current circuit is the amount of work done by the current.

But we understand that the work and power of an electric current is the work of electric field forces moving charges; therefore it is easy to calculate.

The work of transferring an electric charge in an electric field is estimated by multiplying the magnitude of the transferred charge by the magnitude of the potential difference between the points at the beginning and end of the transfer, i.e. by voltage value:

Obviously, this relationship can also be applied to assess concepts such as work and power of electric current. We can judge the amount of charge flowing in the circuit by the current flowing in the circuit and the time it flows, since q = It.

Using this relationship, we obtain a formula expressing the amount of work done by the current on a separate section of the circuit having a voltage U:

The work and power of an electric current are measured as follows: if you measure the current in amperes, the operating time in seconds, and the voltage in volts, then the work is measured in joules (J).

So 1 joule = 1 ampere x 1 volt x 1 second.

Power is measured in watts (W):

1 watt = 1 joule/1 second, or 1 watt = 1 volt x 1 ampere.

The question of calculating the amount of work done by the current in this area is completely unrelated to the question of what type of energy the electrical energy will turn into in this area. This work is a measure of electricity converted into other forms.

Electric current, while performing work, can heat up the filament of an electric lamp, melt metals, rotate the armature of an electric motor, cause chemical transformations, etc. In all cases, the work and power of the electric current determine the level of conversion of electricity into other forms - mechanical energy, thermal motion energy, etc.

Knowing that power P = A/t, we can obtain a formula that can be used to calculate the current power in a separate section of the circuit:

Work and power direct current can be calculated using these formulas, as well as using an ammeter and voltmeter. In practice, the work of the electric field is measured with a special device - a meter. Passing through the meter, a lightweight aluminum disk inside it begins to rotate, and its rotation speed will be directly proportional to the current and voltage. The number of revolutions it will make in certain time, will help draw conclusions about the work accomplished during this time. Electricity meters can be seen in every apartment.

Current power is measured using a special device - a wattmeter. The design of this device combines the principles of a voltmeter and an ammeter.

On many electrical appliances And technical devices their power is indicated. For example, the power of an incandescent light bulb can be 25 W, 75 W, etc., the power of a vacuum cleaner or iron is about 1000 W, the power of electric motors can reach very high values ​​- up to several thousand kilowatts. This refers to the power of the current that passes through a particular device.

Work and power alternating current are calculated differently. So, to calculate the work done by alternating current over a certain period of time, you can use the formula:

P = 1/2I₀U₀ cos φ. Often this formula is written in the following form: P = IU cos φ, where I and U are the voltage and current values, which are 2 times less than the corresponding amplitude values.

The formula for calculating AC power will be the same as for DC.

Units of energy and work:

1 watt-second = 1 J 1 watt-hour = 3600 J;

1 hectowatt-hour = 360,000 J;

1 kilowatt hour = 3600000J.

Power units:

1 ampere-volt = 1 W;

1 hectowatt = 100 W;

/ Electricity

Electricity

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, acquires 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 it flows. 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 called a 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. to his 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:

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. Figure 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
		Platinum-iridium alloy
Metal or alloy
		Manganin (alloy)
Aluminum		Constantan (alloy)
Tungsten
		Nichrome (alloy)
Nickelin (alloy)		Fechral (alloy)
		Chromel (alloy)

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).

Yandex.DirectAll advertisementsApartments for daily rent Kazan! Apartments from 1000 rub. daily. Mini-hotels. Reporting documents16.forguest.ru Apartments for daily rent in Kazan Cozy apartments in all districts of Kazan. Quick daily apartment rental.fatyr.ru New Yandex.Browser! Convenient bookmarks And reliable protection. A browser for pleasant browsing on the Internet!browser.yandex.ru 0+

If you take two conductors isolated from each other, place them on a short distance one from the other, you 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 convenient characteristics 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 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 electrical phenomena and factors.

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

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). A-priory electrical 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:

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:

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:

where r is the conductor resistance. In this case:

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 electric current occurs in the circuit only when exposed to free charges 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 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 a electromotive force, which is called self-induced 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.

What is "electrical work"? What is "work of electric current"?

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).

Irina Parfiryeva

The work done by an electric current shows how much work was done by the electric field when moving charges along a conductor. The work of an electric current is equal to the product of the current strength and the voltage and the time the current flows in the circuit. In order to account for consumed electricity, each apartment is equipped with special electricity meters, which show the work of electric current performed over a certain period of time when various household electrical appliances are turned on. These meters show the work of electric current (electricity consumption) in “kWh”. 1 kW. h = ...W. c = 3,600,000 J