Everything you need to know about electricity. Fundamentals of theoretical electrical engineering for beginners. Electrical engineering is an important science

There are many concepts that you cannot see with your own eyes and touch with your hands. The most striking example is electrical engineering, which consists of complex circuits and obscure terminology. Therefore, many simply retreat before the difficulties of the upcoming study of this scientific and technical discipline.

To gain knowledge in this area will help the basics of electrical engineering for beginners, presented in an accessible language. Supported by historical facts and illustrative examples, they become fascinating and understandable even for those who first encountered unfamiliar concepts. Gradually moving from simple to complex, it is quite possible to study the presented materials and use them in practical activities.

Concepts and properties of electric current

Electrical laws and formulas are required not only for any calculations. They are also needed by those who in practice perform operations related to electricity. Knowing the basics of electrical engineering, you can logically determine the cause of a malfunction and eliminate it very quickly.

The essence of electric current is the movement of charged particles that carry an electric charge from one point to another. However, during random thermal motion of charged particles, following the example of free electrons in metals, charge transfer does not occur. The movement of an electric charge through the cross section of the conductor occurs only under the condition that ions or electrons participate in an ordered movement.

Electric current always flows in a certain direction. Its presence is evidenced by specific signs:

• Heating a conductor through which current flows.
• Change chemical composition conductor under current.
• Rendering a force impact on neighboring currents, magnetized bodies and neighboring currents.

Electric current can be direct and variable. In the first case, all its parameters remain unchanged, and in the second, the polarity changes periodically from positive to negative. In each half-cycle, the direction of the electron flow changes. The rate of such periodic changes is the frequency, measured in hertz.

Basic current quantities

When an electric current occurs in the circuit, there is a constant transfer of charge through the cross section of the conductor. The amount of charge transferred in a certain unit of time is called measured in amperes.

In order to create and maintain the movement of charged particles, the action of a force applied to them in a certain direction is necessary. In the event of termination of such an action, the flow of electric current also stops. Such a force is called the electric field, it is also known as. It is she who causes the potential difference or voltage at the ends of the conductor and gives impetus to the movement of charged particles. To measure this value, a special unit is used - volt. There is a certain relationship between the main quantities, reflected in Ohm's law, which will be discussed in detail.

The most important characteristic of a conductor, directly related to electric current, is resistance, measured in ohms. This value is a kind of counteraction of the conductor to the flow of electric current in it. As a result of the resistance, the conductor is heated. With an increase in the length of the conductor and a decrease in its cross section, the resistance value increases. A value of 1 ohm occurs when the potential difference in the conductor is 1 V, and the current strength is 1 A.

Ohm's law

This law refers to the basic provisions and concepts of electrical engineering. It most accurately reflects the relationship between such quantities as current, voltage, resistance and. The definitions of these quantities have already been considered, now it is necessary to establish the degree of their interaction and influence on each other.

In order to calculate this or that value, you must use the following formulas:

1. Current strength: I \u003d U / R (amps).
2. Voltage: U = I x R (volts).
3. Resistance: R = U/I (ohm).

The dependence of these quantities, for a better understanding of the essence of the processes, is often compared with hydraulic characteristics. For example, at the bottom of a tank filled with water, a valve is installed with a pipe adjacent to it. When the valve is opened, water starts to flow because there is a difference between high pressure at the beginning of the pipe and low - at its end. Exactly the same situation occurs at the ends of the conductor in the form of a potential difference - voltage, under the influence of which the electrons move along the conductor. Thus, by analogy, voltage is a kind of electrical pressure.

The current strength can be compared with the flow of water, that is, its amount flowing through the pipe section for a set period of time. With a decrease in the diameter of the pipe, the flow of water will also decrease due to an increase in resistance. This limited flow can be compared to the electrical resistance of a conductor, which keeps the flow of electrons within certain limits. The interaction of current, voltage and resistance is similar to hydraulic characteristics: with a change in one parameter, all the others change.

Energy and power in electrical engineering

In electrical engineering, there are also such concepts as energy and power associated with Ohm's law. Energy itself exists in mechanical, thermal, nuclear and electrical forms. According to the law of conservation of energy, it cannot be destroyed or created. It can only be transformed from one form to another. For example, audio systems convert electricity into sound and heat.

Any electrical appliance consumes a certain amount of energy over a set period of time. This value is individual for each device and represents the power, that is, the amount of energy that a particular device can consume. This parameter is calculated by the formula P \u003d I x U, the unit of measurement is . It means moving one volt through a resistance of one ohm.

Thus, the basics of electrical engineering for beginners will help at first to understand the basic concepts and terms. After that, it will be much easier to use the acquired knowledge in practice.

Electrics for Dummies: Basics of Electronics

» basic fundamentals of general electrical engineering.

Topic: basic fundamentals of general electrical engineering, electrical engineering for a beginner.

Before becoming an electrician, you first need to know theoretical basis electricity work. After all, what is the difference between an electrician and an ordinary person. And the fact that, due to the theory, which over time was reinforced by practical experience, a person from an ordinary “know-nothing person” turns into an experienced electrical engineer who is fully capable of understanding not only faulty electrical devices, but also who will be able to make a home-made “device”. Such an electrician can be entrusted with any business related to his profession, and he can easily cope with this task without much difficulty.

Electrical engineering for beginners is a cognitive path, gradually passing through which a person builds up professional experience. Do not think that after reading a book on the general theory of electrical engineering, you can immediately learn how to do everything. Even knowing “how to do it”, people in most cases are either afraid to start (knowing about the danger of electricity), or they do it so awkwardly and carelessly that later it is better to redo this work in order to avoid accidental consequences associated with the quality of the functioning of this device, and potential probability of poor electrical safety.

The basics of general electrical engineering are the basics, telling the student what and how it works in general. For example, a person can be given a ready-made instruction “what and how to do consistently”. A capable person will be able to do a certain work according to this plan, and it will be quite correct. But if such a person has to face a case in which there are some previously unknown points (some electrical equipment suddenly broke down and needs to be quickly repaired), then this situation will cause a slight stupor, fussy behavior, and many incorrect and erroneous actions (and this loss of time, energy and nerves).

Electrical engineering for beginners, namely the basics of general electrical engineering, should begin with the simplest laws of physics (electronics section). It is the responsibility of the beginner to learn what electricity is in general, what its properties are, what danger it carries, protection measures and precautions, and so on. Knowledge of this already gives a general idea of ​​\u200b\u200belectricians, as such. Acquainting a person first with difficult-to-understand special subjects (for example, automation, signal theory, etc.) misses the main thing, namely, the assimilation of basic concepts in a figurative language. A "porridge" is formed in the head from a lot of fragmented knowledge, which is very difficult to collect in general model electricity work even smart.

An important factor that greatly affects the quality of teaching electrical engineering for beginners is interest and practice. What do you think is better for beginners to learn, “dry theory”, or step-by-step training, in which some theoretical knowledge is first given in a small dose, followed by practical consolidation (like in chemistry lessons - they talked about the interaction of substances and showed on illustrative example of how it works). Even having assembled the simplest electrical circuit, consisting of a power source, a light bulb, a switch, a rheostat, meters, a person will immediately feel what's what, than just draw the same thing on the board and dryly talk about the circuit.

P.S. I would advise you to delve more into the basic principles of electricity, knowing and understanding them well, further more complex concepts will be given much easier and clearer. Try to figure out on your own the principles of operation of the simplest circuits and the operation of electrical components. After all, complex circuits are many smaller, simpler circuits combined into one.

Everything that will be given in this lesson, it is necessary not only to read and remember some key points, but also to memorize some definitions and formulations. It is from this lesson that elementary physical and electrical calculations will begin. Perhaps not everything will be clear, but do not despair, everything will fall into place over time, the main thing is to slowly absorb and memorize the material. Even if at first not everything is clear, try to at least remember the basic rules and those elementary formulas that will be considered here. Having mastered this lesson well, you will then be able to perform more complex radio engineering calculations and solve the necessary problems. It is impossible to do without it in radio electronics. In order to emphasize the importance of this lesson, I will highlight all the wording and definitions that need to be memorized in red italics.

ELECTRIC CURRENT AND ITS EVALUATION

Until now, when characterizing the quantitative value of the electric current, I sometimes used such terminology as, for example, small current, large current. At first, such an estimate of the current somehow suited us, but it is completely unsuitable for characterizing the current in terms of the work that it can perform. When we talk about the work of current, by this we mean that its energy is converted into some other form of energy: heat, light, chemical or mechanical energy. The greater the flow of electrons, the greater the current and its work. Sometimes they say current or just current. Thus the word current has two meanings. It denotes the very phenomenon of the movement of electric charges in the conductor, and also serves as an estimate of the amount of electricity passing through the conductor. The current (or current strength) is estimated by the number of electrons passing through the conductor for 1 s. Its number is huge. Through the filament of a burning bulb of an electric flashlight, for example, about 2000000000000000000 electrons pass every second. It is quite clear that it is inconvenient to characterize the current by the number of electrons, since one would have to deal with very large numbers. The unit of electric current is taken Ampere (abbreviated as A) . So it was named after the French physicist and mathematician A. Ampère (1775 - 1836), who studied the laws of mechanical interaction of conductors with current and other electrical phenomena. A current of 1 A is a current of such a value at which 6250000000000000000 electrons pass through the cross section of the conductor in 1 s. In mathematical expressions, the current is denoted by the Latin letter I or i (read and). For example, they write: I 2 A or 0.5 A. Along with the ampere, smaller units of current strength are used: milliamp (write mA) equal to 0.001 A, and microampere (write μA) equal to 0.000001 A, or 0.001 mA. Therefore, 1 A = 1000 mA or 1,000,000 µA. Devices used to measure currents are called ammeters, milliammeters, microammeters, respectively. They are included in the electrical circuit in series with the current consumer, i.e. to break the external circuit. In the diagrams, these devices are depicted as circles with the letters assigned to them inside: A (ammeter), (milliammeter) and mA (microampere) μA., and next to it they write RA, which means a current meter. The measuring device is designed for a current not exceeding a certain limit for this device. The device must not be connected to a circuit in which a current exceeding this value flows, otherwise it may deteriorate.

You may have a question: how to evaluate an alternating current, the direction and magnitude of which are constantly changing? Alternating current is usually evaluated by its effective value. This is the value of current that corresponds to direct current producing the same work. The effective value of the alternating current is approximately 0.7 of the amplitude, i.e., the maximum value .

ELECTRICAL RESISTANCE

Speaking of conductors, we mean substances, materials and, above all, metals that conduct current relatively well. However, not all substances, called conductors, conduct electric current equally well, that is, they are said to have unequal current conductivity. This is explained by the fact that during their movement, free electrons collide with atoms and molecules of a substance, and in some substances, atoms and molecules interfere more strongly with the movement of electrons, and in others - less. In other words, some substances have more resistance to electric current, while others have less. Of all the materials widely used in electrical and radio engineering, copper has the least resistance to electric current. Therefore, electrical wires are most often made of copper. Silver has even less resistance, but it is a rather expensive metal. Iron, aluminum and various metal alloys have a high resistance, i.e., the worst electrical conductivity. The resistance of a conductor depends not only on the properties of its material, but also on the size of the conductor itself. A thick conductor has less resistance than a thin conductor of the same material; a short conductor has less resistance, a long one more, just as a wide and short pipe is less of an obstacle to the movement of water than a thin and long one. In addition, the resistance of a metal conductor depends on its temperature: the lower the temperature of the conductor, the lower its resistance. The ohm is taken as the unit of electrical resistance (they write Ohm) - named after the German physicist G. Ohm . A resistance of 1 ohm is a relatively small electrical quantity. For example, a piece of copper wire with a diameter of 0.15 mm and a length of 1 m provides such resistance to current. In radio engineering, one often has to deal with resistances greater than one ohm or several tens of ohms. The resistance of a high-resistance telephone, for example, is greater than 2000 ohms; the resistance of a semiconductor diode connected in a direction that does not pass current is several hundred thousand ohms. Do you know how much electrical resistance your body offers? From 1000 to 20000 ohms. And the resistance of resistors - special parts, which I will talk about in this conversation, can be up to several million ohms or more. These details, as you already know, are indicated in the diagrams in the form of rectangles. In mathematical formulas, resistance is denoted by the Latin letter (R). The same letter is also placed near the graphic designations of resistors in the diagrams. Larger units are used to express large resistances of resistors: kiloohm (abbreviated as kOhm), equal to 1000 Ohms, and megaohm (abbreviated as MΩ), equal to 1,000,000 Ohms, or 1000 kOhm. The resistance of conductors, electrical circuits, resistors or other parts is measured with special instruments called ohmmeters. On the diagrams, an ohmmeter is indicated by a circle with a Greek letter? (omega) inside .

ELECTRICAL VOLTAGE

The unit of electrical voltage, electromotive force (EMF) is the volt (in honor of the Italian physicist A. Volta). In the formulas, voltage is denoted by the Latin letter U (read "y"), and the unit of voltage itself - volt - by the letter V. For example, they write: U = 4.5 V; U \u003d 220 V. The unit volt characterizes the voltage at the ends of the conductor, a section of an electrical circuit or the poles of a current source. A voltage of 1 V is such an electrical quantity that in a conductor with a resistance of 1 Ohm creates a current equal to 1 A. The 3336L battery, designed for a flat pocket electric flashlight, as you already know, consists of three elements connected in series. On the battery label, you can read that its voltage is 4.5 V. This means that the voltage of each of the battery cells is 1.5 V. The voltage of the Krona battery is 9 V, and the voltage of the electric lighting network can be 127 or 220 V. The voltage is measured (with a voltmeter) by connecting the device with the same clamps to the poles of the current source or in parallel with the circuit section, resistor or other load on which it is necessary to measure the voltage acting on it. In the diagrams, the voltmeter is denoted by the Latin letter V .

in a circle, and next - PU. To assess the voltage, a larger unit is also used - kilovolt (write kV), corresponding to 1000 V, as well as smaller units - millivolt (write mV), equal to 0.001 V, and microvolt (write microvolt), equal to 0.001 mV. These voltages are measured accordingly kilo-voltmeters, millivoltmeters and microvoltmeters. Such devices, like voltmeters, are connected in parallel to current sources or sections of circuits on which voltage must be measured. Let us now find out what is the difference between the concepts of "voltage" and "electromotive force". The electromotive force is the voltage acting between the poles of a current source until an external load circuit is connected to it, for example, an incandescent light bulb or a resistor. As soon as an external circuit is connected and a current appears in it, the voltage between the poles of the current source will decrease. So, for example, a new galvanic cell that has not yet been in use has an EMF of at least 1.5 V. When a load is connected to it, the voltage at its poles becomes approximately 1.3-1.4 V. As the energy of the element is consumed to power the external circuit, its voltage gradually decreases. The cell is considered discharged and therefore unusable when the voltage drops to 0.7 V, although if the external circuit is turned off, its EMF will be greater than this voltage. How is voltage measured? When they talk about alternating voltage, for example, the voltage of an electric lighting network, they mean its effective value, which is approximately, like the effective value of alternating current, 0.7 of the amplitude value of the voltage.

OHM'S LAW

On fig. shows a diagram of a familiar to you the simplest electrical circuit. This closed circuit consists of three elements: a voltage source - a battery GB, a current sink - a load R, which can be, for example, a filament of an electric lamp or a resistor, and conductors connecting the voltage source to the load. By the way, if this circuit is supplemented with a switch, it will turn out full scheme pocket electric flashlight.

The load R, which has a certain resistance, is a section of the circuit. The value of the current in this section of the circuit depends on the voltage acting on it and its resistance: the higher the voltage and the lower the resistance, the greater the current will flow through the section of the circuit. This dependence of current on voltage and resistance is expressed by the following formula:
I = U/R,
where I is the current expressed in amperes, A; U - voltage in volts, V; R - resistance in ohms, Ohm. This mathematical expression is read as follows: the current in a circuit section is directly proportional to the voltage on it and inversely proportional to its resistance. This is the basic law of electrical engineering, called Ohm's law (by the name of G. Ohm), for a section of an electrical circuit . Using Ohm's law, it is possible to find out an unknown third from two known electrical quantities. Here are some examples of the practical application of Ohm's law.

First example: On a section of the circuit with a resistance of 5 ohms, a voltage of 25 V operates. It is necessary to find out the value of the current in this section of the circuit.
Solution: I \u003d U / R \u003d 25 / 5 \u003d 5 A.
Second example: A voltage of 12 V acts on the circuit section, creating a current equal to 20 mA in it. What is the resistance of this section of the circuit? First of all, the current of 20 mA must be expressed in amperes. This will be 0.02 A. Then R \u003d 12 / 0.02 \u003d 600 Ohms.

Third example: A current of 20 mA flows through a section of a circuit with a resistance of 10 kΩ. What is the voltage acting on this part of the circuit? Here, as in the previous example, the current must be expressed in amperes (20 mA = 0.02 A), resistance in ohms (10kΩ = 10000Ω). Therefore, U \u003d IR \u003d 0.02 x 10000 \u003d 200 V. The base of the incandescent lamp of a flat pocket lamp is stamped: 0.28 A and 3.5 V. What does this information say? The fact that the light bulb will glow normally at a current of 0.28 A, which is determined by a voltage of 3.5 V. Using Ohm's law, it is easy to calculate that the incandescent filament of the light bulb has a resistance of R = 3.5 / 0.28 = 12.5 Ohm . This, I emphasize, is the resistance of the incandescent filament of the light bulb. And the resistance of the cooled thread is much less. Ohm's law is valid not only for the site, but for the entire electrical circuit. In this case, the total resistance of all elements of the circuit, including the internal resistance of the current source, is substituted into the value of R. However, in the simplest circuit calculations, the resistance of the connecting conductors and the internal resistance of the current source are usually neglected.

In this regard, I will give another example: The voltage of the electric lighting network is 220 V. What current will flow in the circuit if the load resistance is 1000 Ohm? Solution: I \u003d U / R \u003d 220 / 1000 \u003d 0.22 A. Approximately this current is consumed by an electric soldering iron.

All these formulas, which follow from Ohm's law, can also be used to calculate AC circuits, but provided that there are no inductors and capacitors in the circuits.

Ohm's law and the calculation formulas derived from it are quite easy to remember if you use this graphical scheme, the so-called. Ohm's law triangle:

It is easy to use this triangle, it is quite clear to remember that the horizontal line in the triangle means the division sign (by analogy with the fractional bar), and the vertical line in the triangle means the multiplication sign .

Now consider this question: how does a resistor connected in series with a load or in parallel with it affect the current? Let's take an example. We have a bulb from a round electric lamp, rated for a voltage of 2.5 V and a current of 0.075 A. Can this bulb be powered by a 3336L battery, the initial voltage of which is 4.5 V? It is easy to calculate that the incandescent filament of this light bulb has a resistance of a little more than 30 ohms. If you feed it from a fresh 3336L battery, then, according to Ohm's law, a current will go through the filament of the light bulb, almost twice the current for which it is designed. The thread will not withstand such an overload, it will overheat and collapse. But this light bulb can still be powered from a 336L battery if an additional resistor with a resistance of 25 ohms is connected in series with the circuit, as shown in Fig.

In this case, the total resistance of the external circuit will be approximately 55 ohms, i.e. 30 Ohm - the resistance of the light bulb filament H plus 25 Ohm - the resistance of the additional resistor R. Therefore, a current equal to approximately 0.08 A will flow in the circuit, i.e. almost the same as the filament of a light bulb. This light bulb can be powered from a battery with a higher voltage, and even from an electric lighting network, if you choose a resistor of the appropriate resistance. In this example, the additional resistor limits the current in the circuit to the value we need. The greater its resistance, the less current in the circuit will be. AT this case Two resistances were connected in series in the circuit: the resistance of the light bulb filament and the resistance of the resistor. And with a series connection of resistances, the current is the same at all points in the circuit. You can turn on the ammeter at any point in the circuit, and everywhere it will show one value. This phenomenon can be compared to the flow of water in a river. The riverbed in different areas can be wide or narrow, deep or shallow. However, for a certain period of time, the same amount of water always passes through the cross section of any section of the river channel.

Additional resistor , included in the circuit in series with the load (as, for example, in the figure above), can be considered as a resistor, "extinguishing" part of the voltage acting in the circuit. The voltage that is quenched by an additional resistor, or, as they say, drops across it, will be the greater, the greater the resistance of this resistor. Knowing the current and resistance of the additional resistor, it is easy to calculate the voltage drop across it using the same familiar formula U \u003d IR, Here U is the voltage drop, V; I - current in the circuit, A; R is the resistance of the additional resistor, Ohm. In relation to our example, the resistor R (in the figure) extinguished the excess voltage: U \u003d IR \u003d 0.08 x 25 \u003d 2 V. The rest of the battery voltage, equal to approximately 2.5 V, fell on the light bulb filaments. The required resistance of the resistor can be found by another formula familiar to you R \u003d U / I, where R is the desired resistance of the additional resistor, Ohm; U-voltage to be extinguished, V; I - current in the circuit, A. For our example, the resistance of the additional resistor is: R \u003d U / I \u003d 2 / 0.075, 27 Ohm. By changing the resistance, you can reduce or increase the voltage that drops across the additional resistor, and thus regulate the current in the circuit. But the additional resistor R in such a circuit can be variable, i.e. resistor, the resistance of which can be changed (see figure below).

In this case, using the resistor slider, you can smoothly change the voltage supplied to the load H, which means you can smoothly adjust the current flowing through this load. A variable resistor connected in this way is called a rheostat. With the help of rheostats, the currents in the circuits of receivers, televisions and amplifiers are regulated. In many cinemas, rheostats were used to smoothly dim the lights in the auditorium. There is, however, another way to connect the load to a current source with excess voltage - also using a variable resistor, but switched on by a potentiometer, i.e. voltage divider as shown in Fig.

Here R1 is a resistor connected by a potentiometer, and R2 is a load, which can be the same incandescent bulb or some other device. On the resistor R1 there is a voltage drop of the current source, which can be partially or completely supplied to the load R2. When the resistor slider is in its lowest position, no voltage is supplied to the load at all (if it is a light bulb, it will not light). As the resistor slider moves up, we will apply more and more voltage to the load R2 (if this is a light bulb, its filament will glow). When the slider of the resistor R1 is in its highest position, the entire voltage of the current source will be applied to the load R2 (if R2 is a flashlight bulb, and the voltage of the current source is large, the bulb filament will burn out). You can empirically find such a position of the variable resistor engine at which the voltage it needs will be applied to the load. Variable resistors, switched on by potentiometers, are widely used to control the volume in receivers and amplifiers. The resistor can be directly connected in parallel with the load. In this case, the current in this section of the circuit branches and goes in two parallel ways: through an additional resistor and the main load. The greatest current will be in the branch with the least resistance. The sum of the currents of both branches will be equal to the current consumed to power the external circuit. Parallel connection is resorted to in those cases when it is necessary to limit the current not in the entire circuit, as in the series connection of an additional resistor, but only in some area. Additional resistors are connected, for example, in parallel with milliammeters so that they can measure large currents. Such resistors are called bypass or shunts . The word shunt means branch .

INDUCTIVE RESISTANCE

In an alternating current circuit, the current value is affected not only by the resistance of the conductor included in the circuit, but also by its inductance. Therefore, in AC circuits, the so-called ohmic or active resistance, determined by the properties of the material of the conductor, and inductive resistance, determined by the inductance of the conductor, are distinguished. A straight conductor has a relatively small inductance. But if this conductor is wound into a coil, its inductance will increase. At the same time, the resistance provided by it to alternating current will also increase - the current in the circuit will decrease. As the frequency of the current increases, the inductive reactance of the coil also increases. Remember: the resistance of an inductor to alternating current increases with an increase in its inductance and the frequency of the current passing through it. This property of the coil is used in various receiver circuits when it is necessary to limit the high frequency current or isolate high frequency oscillations, in alternating current rectifiers and in many other cases that you will constantly encounter in practice. The unit of inductance is the henry (H). Such a coil has an inductance of 1Hn, in which, when the current in it changes by 1 A, within 1 s, an EMF of self-induction develops equal to 1 V. This unit is used to determine the inductance of coils that are included in audio frequency current circuits. The inductance of the coils used in oscillatory circuits is measured in thousandths of a henry, called millihenry (mH), or a thousand times smaller unit - microhenry (mH) .

POWER AND CURRENT WORK

A certain amount of electricity is expended on heating the filament of an electric or electronic lamp, electric soldering iron, electric stove or other device. This energy, given by the current source (or received from it by the load) for 1 s, is called current power. For a unit of current power is taken watt (W) . Watt is the power that a constant current of 1A develops at a voltage of 1V. In the formulas, the current power is denoted by the Latin letter P (read "pe"). Electrical power in watts is obtained by multiplying the voltage in volts by the current in amperes, i.e. P=U.I. If, for example, a 4.5 V direct current source creates a current of 0.1 A in the circuit, then the current power will be: p \u003d 4.5 x 0.1 \u003d 0.45 W. Using this formula, you can, for example, calculate the power consumed by a flashlight bulb if 3.5 V is multiplied by 0.28 A. We get about 1 watt. By changing this formula to: I \u003d P / U, you can find out the current flowing through an electrical device if you know the power consumed by it and the voltage supplied to it. What, for example, is the current flowing through an electric soldering iron if it is known that at a voltage of 220 V it consumes 40 W of power? I \u003d P / I \u003d 40/220 \u003d 0.18 A. If the current and resistance of the circuit are known, but the voltage is unknown, the power can be calculated using the following formula: P \u003d I2R. When the voltage acting in the circuit and the resistance of this circuit are known, then the following formula is used to calculate the power: P \u003d U2 / R. But a watt is a relatively small unit of power. When you have to deal with electrical devices, appliances or machines that consume currents of tens, hundreds of amperes, use the unit of kilowatt power (write kW), equal to 1000 watts. The power of electric motors of factory machines, for example, can range from several units to tens of kilowatts. The quantitative consumption of electricity is estimated by the watt - a second, which characterizes the unit of energy - the joule. The power consumption is determined by multiplying the power consumed by the device by the time of its operation in seconds. If, for example, the bulb of an electric flashlight (its power, as we already know, is about 1 W) burned for 25 seconds, then the energy consumption was 25 watts - seconds. However, the watt-second value is very small. Therefore, in practice, larger units of electricity consumption are used: watt - hour, hectowatt - hour and kilowatt - hour. In order for the energy consumption to be expressed in watt-hours or kilowatt-hours, it is necessary to multiply the power in watts or kilowatts by the time in hours, respectively. If, for example, the device consumes a power of 0.5 kW for 2 hours, then the energy consumption will be 0.5 X 2 \u003d 1 kWh; 1 kWh of energy will also be consumed if the circuit consumes (or consumes) 2 kW for half an hour, 4 kW for a quarter of an hour, etc. An electric meter installed in the house or apartment where you live takes into account the consumption of electricity in kilowatt-hours. By multiplying the meter reading by the cost of 1 kWh (amount in kopecks), you will find out how much energy was spent per week, month. When working with galvanic cells or batteries, they talk about their electrical capacity in ampere - hours, which is expressed as the product of the value of the discharge current and the duration of work in hours. The initial battery capacity is 3336L, for example 0.5 Ah. Calculate: how long will the battery work continuously if it is discharged with a current of 0.28 A (the current of a flashlight bulb)? Approximately one and three quarters of an hour. If this battery is discharged more intensively, for example, with a current of 0.5 A, it will work for less than 1 hour. Thus, knowing the capacity of the galvanic cell or battery and the currents consumed by their loads, we can calculate the approximate time during which these chemical current sources. The initial capacity, as well as the recommended discharge current or external circuit resistance, which determines the discharge current of a cell or battery, is sometimes indicated on their labels or in reference literature.

In this lesson, I tried to systematize and lay out the maximum information necessary for a beginner radio amateur on the basics of electrical engineering, without which there is no point in continuing to study something. The lesson turned out to be perhaps the longest, but also the most important. I advise you to take this lesson more seriously, be sure to memorize the highlighted definitions, if something is not clear, re-read it several times to understand the essence of what was said. As practical work, you can experiment with the circuits shown in the figures, i.e. with batteries, light bulbs and a variable resistor. This will do you good. In general, in this lesson, of course, all the emphasis should be placed not on practice, but on mastering the theory.

If an electrical unit fails, the right decision would be to call a specialist who will quickly fix the problem.

If this is not possible, lessons for electricians will help to fix this or that breakdown on their own.

At the same time, it is worth remembering safety precautions in order to avoid serious injuries.

Safety

Safety rules must be learned by heart - this will save health and life when eliminating problems with electricity. Here are the most important electrical basics for beginners:

To perform installation work, you must purchase a sensor (phase indicator), similar to a screwdriver or an awl. This device allows you to find a wire that is energized - when it is detected, an indicator lights up on the sensor. The devices work differently, for example, when the corresponding contact is pressed with a finger.

Before starting work, you must use the indicator to make sure that all wires are not de-energized.

The fact is that sometimes the wiring is laid incorrectly - the machine at the entrance turns off only one wire without de-energizing the entire network. Such a mistake can lead to sad consequences, because a person hopes for a complete shutdown of the system, while some area may still be active.

Types of circuits, voltage and current

Electrical circuits can be connected in parallel or in series. In the first case, the electric current is distributed over all circuits that are connected in parallel. It turns out that the total unit will be equal to the sum of the current in any of the circuits.

Parallel connections have the same voltage. In a series combination, current flows from one system to another. As a result, the same current flows in each line.

It makes no sense to dwell on the technical definitions of voltage and current (A). It will be much clearer to explain with examples. So, the first parameter affects how well you need to isolate different areas. The larger it is, the higher the probability that a breakdown will occur in some place. It follows that high voltage requires high-quality insulation. Bare connections must be kept away from each other, from other materials and from the ground.

Electrical voltage (U) is usually measured in Volts.

More powerful voltage carries a greater threat to life. But do not assume that low is absolutely safe. The danger to a person also depends on the strength of the current that passes through the body. And this parameter is already directly subordinate to resistance and voltage. At the same time, the resistance of the body is associated with the resistance of the skin, which can vary depending on the moral and physical condition of the person, humidity and many other factors. There have been cases when a person died from an electric shock of only 12 volts.

In addition, depending on the strength of the current, various wires are selected. The higher A, the thicker the wire needed.

Variable and constant

When electricity was in its infancy, direct current was supplied to consumers. However, it turned out that the standard value of 220 volts is almost impossible to transmit over a long distance.

On the other hand, thousands of volts cannot be supplied - firstly, it is dangerous, and secondly, it is difficult and expensive to manufacture devices operating at such a high voltage. As a result, it was decided to convert the voltage - 10 volts reach the city, and 220 already gets into the houses. The conversion takes place using transformer.

As for the voltage frequency, it is 50 Hertz. This means that the voltage changes its state 50 times per minute. It starts from zero and rises to 310 volts, then drops to zero, then to -310 volts and rises to zero again. All work proceeds in a cyclic manner. In such cases, the voltage in the network is 220 volts - why not 310, will be discussed further. Abroad, there are different parameters - 220, 127 and 110 volts, and the frequency can be 60 hertz.

Power and other parameters

Electrical current is needed to do some work, such as turning a motor or heating batteries. You can calculate how much work it will do by multiplying the current by the voltage. For example, an electric heater that has 220 volts and has a power of 2.2 kW will consume a current of 10 A.

The standard measurement of power is in watts (W). An electric current of 1 ampere with a voltage of 1 volt can produce 1 watt of power.

The above formula is used for both types of current. However, the calculation of the first has some complexity - it is necessary to multiply the current by U in each unit of time. And if we take into account that the voltage and power indicators of alternating current change all the time, then we will have to take the integral. Therefore, the concept was applied effective value.

Roughly speaking, the effective parameter is the average value of the current and voltage, chosen in a special way.

Alternating and direct current has an amplitude and current state. The amplitude parameter is the maximum unit to which the voltage can rise. For a variable type, the amplitude number is equal to the current multiplied by √ 2. This explains the voltage indicators of 310 and 220 V.

Ohm's law

The next concept in the basics of electricians for beginners is Ohm's law. He states that current is equal to voltage divided by resistance. This law applies to both AC and DC.

Resistance is measured in ohms. So, through a conductor with a resistance of 1 ohm at a voltage of 1 volt, a current of 1 ampere passes. Ohm's law gives rise to two interesting consequences:

• If the A flowing through the system and the resistance of the circuit are known, then the power can be calculated.
• Power can also be calculated knowing the effective resistance and U.

In this case, to determine the power, it is not the mains voltage that is taken, but U applied to the conductor. It turns out that if any device is connected to the system through an extension cord, then the action will be applied both to the device and to the wires of the extension device. As a result, the wires will heat up.

Of course, it is undesirable for the connections to heat up, since this is what leads to various malfunctions of the electrical wiring.

However, the main problems are not in the wire itself, but in the various junctions. At these points, the resistance is ten times higher than along the perimeter of the wire. Over time, as a result of oxidation, the resistance can only increase.

Particularly dangerous are the junctions of various metals. In them, the oxidation processes are much faster. The most frequent connection zones:

• Places of twisting wires.
• Terminals of switches, sockets.
• Clamp contacts.
• Contacts in switchboards.
• Plugs and sockets.

Therefore, when repairing, the first thing to do is pay attention to these areas. They must be accessible for installation and control.

By following the rules described above, you can independently solve some household issues related to the electrician in the house. The main thing is to remember safety precautions.

Let's start with the concept of electricity. Electric current is the ordered movement of charged particles under the influence of an electric field. The free electrons of the metal can act as particles if the current flows through a metal wire, or ions if the current flows in a gas or liquid.
There is also a current in semiconductors, but this is a separate topic for discussion. An example is a high-voltage transformer from a microwave oven - first, electrons run through the wires, then ions move between the wires, respectively, first the current goes through the metal, and then through the air. A substance is called a conductor or semiconductor if it contains particles capable of carrying an electric charge. If there are no such particles, then such a substance is called a dielectric, it does not conduct electricity. Charged particles carry an electrical charge, which is measured as q in coulombs.
The unit of measurement of current strength is called Ampere and is denoted by letter I, a current of 1 Ampere is formed when a charge of 1 Coulomb passes through a point in an electrical circuit in 1 second, that is, roughly speaking, the current strength is measured in coulombs per second. And in fact, the current strength is the amount of electricity flowing per unit of time through the cross section of the conductor. The more charged particles run through the wire, the correspondingly more current.
To make charged particles move from one pole to another, it is necessary to create a potential difference between the poles or - Voltage. Voltage is measured in volts and is denoted by the letter V or U. To get a voltage of 1 Volt, you need to transfer a charge of 1 C between the poles, while doing work of 1 J. I agree, it’s a little incomprehensible.

For clarity, imagine a tank of water located at a certain height. A pipe comes out of the tank. Water flows out through the pipe under the influence of gravity. Let the water be an electric charge, the height of the water column be the voltage, and the speed of the water flow be the electric current. More precisely, not the flow rate, but the amount of water flowing out per second. You understand that the higher the water level, the greater the pressure below. And the higher the pressure below, the more water will flow out through the pipe, because the speed will be higher .. Similarly, the higher the voltage, the more current will flow in the circuit.

The relationship between all three considered quantities in a DC circuit defines the Ohm's law, which is expressed by this formula, and sounds like the current in the circuit is directly proportional to the voltage, and inversely proportional to the resistance. The more resistance, the less current, and vice versa.

Let me add a few more words about resistance. It can be measured, but it can be calculated. Let's say we have a conductor that has a known length and cross-sectional area. Square, round, whatever. Different substances have different resistivity, and for our imaginary conductor there is such a formula that determines the relationship between length, cross-sectional area and resistivity. The resistivity of substances can be found on the Internet in the form of tables.
You can again draw an analogy with water: water flows through a pipe, let the pipe have a specific roughness. It is logical to assume that the longer and narrower the pipe, the less water will flow through it per unit of time. See how simple it is? You don’t even need to memorize the formula, just imagine a pipe with water.
As for measuring resistance, you need a device, an ohmmeter. Nowadays, universal devices are more popular - multimeters, they measure resistance, current, voltage, and a bunch of other things. Let's do an experiment. I will take a piece of nichrome wire of known length and cross-sectional area, find the resistivity on the site where I bought it and calculate the resistance. Now I will measure the same piece with the help of the device. For such a small resistance, I will have to subtract the resistance of the probes of my device, which is equal to 0.8 ohms. That's it!
The multimeter scale is divided by the size of the measured values, this is done for more high precision measurements. If I want to measure a 100 kΩ resistor, I turn the knob to the higher nearest resistance. In my case, this is 200 kilo-ohms. If I want to measure 1 kilo-ohm, then I put on 2 com. This is true for the measurement of other quantities. That is, the limits of the measurement in which you need to get are set on the scale.
Let's continue to play with the multimeter and try to measure the rest of the studied quantities. I'll take several different sources of direct current. Let it be a 12 volt power supply, a USB port and a transformer, which my grandfather made in his youth.
We can measure the voltage at these sources right now by connecting a voltmeter in parallel, that is, directly to the plus and minus of the sources. With tension, everything is clear, it can be taken and measured. But to measure the strength of the current, you need to create an electrical circuit through which the current will flow. There must be a consumer or load in the electrical circuit. Let's connect a consumer to each source. A piece of LED strip, a motor and a resistor (160 ohms).
Let's measure the current flowing in the circuits. To do this, I switch the multimeter to the current measurement mode and switch the probe to the current input. The ammeter is connected in series to the measured object. Here is the diagram, it should also be remembered and not confused with connecting a voltmeter. By the way, there is such a thing as current clamps. They allow you to measure the current in a circuit without connecting directly to the circuit. That is, you do not need to disconnect the wires, just throw them on the wire and they measure. Okay, back to our usual ammeter.

So, I measured all the currents. Now we know how much current is consumed in each circuit. Here we have LEDs glowing, here the motor is spinning, and here .... So stand, but what does the resistor do? He does not sing songs to us, does not light up the room and does not rotate any mechanism. So what does he spend as much as 90 milliamps on? That won't work, let's see. Hey you! Aw, he's hot! So that's where the energy goes! Is it possible to somehow calculate what kind of energy is here? It turns out - it is possible. The law describing the thermal effect of electric current was discovered in the 19th century by two scientists, James Joule and Emil Lenz.
The law is called Lenz's joule law. It is expressed by such a formula, and numerically shows how many joules of energy are released in the conductor in which the current flows, per unit of time. From this law, you can find the power that is released on this conductor, the power is denoted English letter R is measured in watts. I found this very cool tablet that links all the quantities we have studied so far.
So on my table electric power goes to lighting, to perform mechanical work and to heat the surrounding air. By the way, it is on this principle that various heaters, electric kettles, hair dryers, soldering irons and so on work. There is a thin spiral everywhere, which heats up under the influence of current.

This point should be taken into account when connecting wires to the load, that is, laying wiring to sockets around the apartment is also included in this concept. If you take too thin wire to the outlet and plug a computer, kettle and microwave into this outlet, the wire can heat up until a fire starts. Therefore, there is such a plate that connects the cross-sectional area of ​​\u200b\u200bthe wires with the maximum power that will go through these wires. If you decide to pull the wires - do not forget about it.

Also within the framework of this issue, I would like to recall the features of parallel and series connection of current consumers. When connected in series, the current strength is the same for all consumers, the voltage is divided into parts, and the total resistance of consumers is the sum of all resistances. With a parallel connection, the voltage on all consumers is the same, the current strength is divided, and the total resistance is calculated using this formula.
One very interesting point follows from this, which can be used to measure the current strength. Let's say you need to measure the current in the circuit about 2 amperes. The ammeter does not cope with this task, so you can use the Ohm's law in its purest form. We know that the current strength is the same when connected in series. Take a resistor with a very small resistance and insert it in series with the load. Let's measure the voltage on it. Now, using Ohm's law, we find the current strength. As you can see, it coincides with the calculation of the tape. The main thing to remember here is that this additional resistor should be as low as possible in order to have a minimal effect on measurements.

There is another very important point that you need to know about. All sources have a maximum output current, if this current is exceeded, the source may heat up, fail, and in the worst case, even catch fire. The most favorable outcome is when the source has overcurrent protection, in which case it will simply turn off the current. As we remember from Ohm's law, the lower the resistance, the higher the current. That is, if you take a piece of wire as a load, that is, close the source to itself, then the current in the circuit will jump to huge values, this is called a short circuit. If you remember the beginning of the release, you can draw an analogy with water. If we substitute zero resistance into Ohm's law, then we get an infinitely large current. In practice, of course, this does not happen, because the source has an internal resistance that is connected in series. This law is called Ohm's law for a complete circuit. Thus, the short circuit current depends on the value of the internal resistance of the source.
Now let's get back to the maximum current that the source can produce. As I said, the current strength in the circuit determines the load. Many wrote to me on VK and asked something like this, I exaggerate it a little: Sanya, I have a 12 volt and 50 amp power supply. If I connect a small piece of LED strip to it, will it not burn out? No, of course it won't burn. 50 amps is the maximum current that the source is capable of delivering. If you connect a piece of tape to it, it will take its well, let's say 100 milliamps, and that's it. The current in the circuit will be equal to 100 milliamps, and no one will burn anywhere. Another thing is, if you take a kilometer of LED strip and connect it to this power supply, then the current there will be higher than the permissible one, and the power supply will most likely overheat and fail. Remember, it is the consumer who determines the amount of current in the circuit. This block can deliver a maximum of 2 amps, and when I short it to a bolt, nothing happens to the bolt. But the power supply does not like it, it works in extreme conditions. But if you take a source capable of delivering tens of amperes, the bolt will not like this situation.

For example, let's calculate the power supply that will be required to power a known segment of the LED strip. So, we bought a coil of LED strip from the Chinese and we want to power three meters of this very strip. First, we go to the product page and try to find how many watts one meter of tape consumes. I could not find this information, so there is such a sign. Let's see what kind of tape we have. Diodes 5050, 60 pieces per meter. And we see that the power is 14 watts per meter. I want 3 meters, so the power will be 42 watts. It is advisable to take the power supply with a margin of 30% in terms of power so that it does not work in a critical mode. As a result, we get 55 watts. The nearest suitable power supply will be 60 watts. From the power formula, we express the current strength and find it, knowing that the LEDs operate at a voltage of 12 volts. It turns out that we need a block with a current of 5 amperes. We go, for example, to Ali, we find, we buy.
It is very important to know the current consumption when making any USB homemade products. The maximum current that can be taken from USB is 500 milliamps, and it is better not to exceed it.
And finally, a little about safety. Here you can see to what values ​​electricity is considered harmless to human life.