Electrical engineering in simple terms. Tips for all occasions. What books will help you learn electronics
The desire of people of any age to comprehend such a science as electrical engineering is understandable. The basics of electrical engineering for all beginners will help in this. A lot of materials are published on the Internet and in print, often under the title "Electrical Engineering for Dummies". You need to start with the assimilation of the provisions and laws of electricity.
Concepts and properties of electric current
The initial courses of an electrician in the first chapters give definitions to the concept and properties of electric current, explain the nature and properties of electricity, the laws of electricity and their basic formulas. Based on the great discoveries, such a scientific discipline as electrical engineering was born and received a grandiose development. The essence of electricity lies in the directed movement of electrons (charged particles). They carry an electric charge in the body of metal wires.
Important! For the transit of electrical energy, wires are used, the cores of which are made of aluminum or copper. These are the most economical conductive metals. Making wire cores from other materials is expensive, therefore unprofitable.
Current can be direct and variable direction. The constant movement of energy is always carried out in one direction. The variable energy flow rhythmically changes its polarity. The rate at which the direction of electron movement changes is called the frequency. It is measured in hertz.
What does electrical engineering study
The basis of electrics was formed in the 19th century. Those times are called the era of grandiose discoveries of fundamental laws that give all ideas about electricity. Electrical engineering (ET) as a science began to take its first steps. Theory was reinforced by practice. The first electrical devices appeared, communication systems for delivering electricity from the source to the consumer were improved.
The achievements in the field of physics, chemistry and mathematics became the basis for the development of electrical engineering. The new science studied the properties of electric current, the nature of electromagnetic radiation and other processes. As knowledge accumulated, ET became an applied science.
A modern scientific discipline studies devices that use electric current. On the basis of research, new more advanced electrical installations, devices and devices are being created. ET is one of the advanced sciences, which is one of the main engines of the progress of human civilization.
Where to start learning the basics of electrical engineering
Electrical engineering for beginners is available on many information media. Modern means mass media are not short of tutorials on the basics of electricity. Electricity tutorials are purchased on the Internet or bookstores. A beginner can get electrician lessons in the form of a free video course on the basics of electricity via the Internet. Online video lectures in an accessible form teach everyone the basics of electricity.
Note! The book, despite the available video resources on the web, is still considered the most convenient source of information. Using the tutorial on electrics from scratch, you do not need to turn on the PC all the time. The textbook will always be at hand.
Tutorials serve as indispensable helpers in order to repair electrical wiring, repair a switch, a socket, install a motion sensor and replace fuses in household electrical appliances.
Main current characteristics
The main characteristics include current, voltage, resistance and power. The parameters of the electric current flowing through the wire are characterized by precisely these values.
Current strength
The parameter means the amount of charge passing through the wire in a certain time. Current is measured in amperes.
Voltage
This is nothing but the potential difference between two points of the conductor. The value is measured in volts. One volt is the potential difference at which it takes one joule of work to transfer a charge of 1 coulomb.
Resistance
This parameter is measured in ohms. Its value determines the resistance to energy flow. The greater the mass and cross-sectional area of the conductor, the greater the resistance. It also depends on the material and length of the wire. With a potential difference at the ends of the conductor of 1 volt and a current strength of 1 ampere, the resistance of the conductor is 1 ohm.
Power
The physical quantity expresses the speed of the flow of electricity in the conductor. The power of the current is determined by the product of the current and voltage. The unit of power is watt.
Comprehension of the basics of electrical engineering must begin with Ohm's law. It is he who is the foundation of the whole science of electricity. The outstanding German physicist Georg Simon Om in 1826 formulated a law in which he determines the interdependence of the three main parameters of electric current: strength, voltage and resistance.
Energy and power in electrical engineering
Electrician for beginners explains the terms of energy and power. These characteristics are directly related to Ohm's law. Energy can flow from one form to another. That is, it can be nuclear, mechanical, thermal and electrical.
In the speakers of sound devices, the potential of the electric current is converted into the energy of sound waves. In electric motors, the current energy flow is converted into mechanical energy, which causes the motor rotor to rotate.
Any electrical device consumes the right amount of electricity for a certain period of time. The amount of energy consumed per unit of time is the power of the consumer of electricity. More detailed interpretation powers can be found in chapters study guide dedicated to electromechanics for beginners.
Power is determined by the formula:
This parameter is measured in watts. The unit of power is watts, which means that a current of one ampere is moved by a voltage of 1 volt. In this case, the resistance of the conductor is equal to 1 ohm. This interpretation of the current characteristic is most understandable for beginners to comprehend the basics of electricity.
Electrical engineering and electromechanics
Electrical mechanics is a branch of electrical engineering. This scientific discipline studies circuit diagrams equipment, motors and other devices that use electrical energy.
After completing the electromechanics course for beginners, beginners can independently learn how to repair household electrical devices and appliances. The basic laws of electromechanics make it possible to understand how an electric motor works, how a transformer differs from a stabilizer, what a generator is, and much more.
Safety and practice
The Basics of Electrical Engineering for Beginners emphasizes safety rules. Failure to comply with them in practice can sometimes cause electrical injury and damage to property. For beginners in electrical engineering, you must follow the four basic requirements of safety.
Four safety rules for beginners:
- Before working with any device or equipment, you should read its documentation. All instruction manuals have a safety section. It describes dangerous activities, which may cause short circuit or electric shock.
- Before working on electrical devices or electrical wiring, you need to turn off the electricity. Then inspect the condition of the insulation of the conductors. If a violation of the insulating coating is detected, then the bare part of the conductors must be covered with a piece of insulating tape.
- When working with wiring and equipment energized by a household power supply, dielectric gloves, goggles and shoes with thick rubber soles should be used. In electrical distribution cabinets, switchboards and electrical installations, beginners have nothing to do at all. They are carried out by qualified electricians who have access to work under voltage.
- Never touch bare conductors with your hands. To do this, there are probe screwdrivers, multimeters and other electrical measuring instruments. Only after making sure that there is no voltage, you can touch the wires.
Electricity for dummies
Electronics surrounds a person in the form of various devices and devices. Modern household appliances are mostly controlled by electronic circuits. Basic electronics training courses for beginners are aimed at ensuring that a beginner can distinguish a transistor from a resistor and understand how and what this or that electronic circuit serves.
Tutorials and video courses help to understand the principles of building electronic circuits. What is a printed circuit board, how to create a circuit with your own hands - all these questions are answered by the basics of electronics for beginners. Having mastered the basics of electronics, the home "master" will be able to determine the failed radio component in the TV, audio device and other household appliances and replace it. In addition, the beginner will gain experience with a soldering iron.
Video courses, printed materials carry a lot of information on mastering the basics of electrical engineering, electromechanics and electronics. You can acquire knowledge in these areas without leaving your home. View the desired video, order textbooks allows the availability of the Internet.
Video
Speaking about the property of a body to prevent the passage of electric current through it, we usually use the term "electrical resistance". In electronics, it is convenient, there are even special microelectronic components, resistors with one or another nominal resistance.But there is also the concept of "electrical conductivity" or "electrical conductivity", which characterizes the ability of a body to conduct electric current. Whereas resistance is inversely proportional to current, conductance is directly proportional to current...
The Latin word "polus" comes from the Greek "stripes". In a broad sense, this term denotes a limit, border or extreme point of something, something one thing, diametrically opposed to another, when it comes to, for example, two poles.Our planet has north and south geographic poles - opposite edges of the globe relative to the equator, as well as magnetic poles (like a permanent magnet). A permanent magnet has a north and south pole They tend to be attracted to each other. In the same way, the poles of the current source indicate its peculiar boundaries ...
The amount of current flowing through a conductor is directly proportional to the voltage at its ends. This means that the greater the voltage at the ends of the conductor, the greater the current in this conductor. But with the same voltage on different conductors made of different materials, the magnitude of the current will be different. That is, if the voltage on different conductors is increased equally, then the increase in the magnitude of the current will occur in different conductors in different ways, and this depends on the properties of a particular conductor.For any conductor, the dependence of the magnitude of the current on the applied voltage is individual ...
To measure the magnitude of the current in the circuits of direct and alternating current, an electrical ammeter is used. The ammeter is connected in series with the current source.Since the current is an ordered movement of charged particles along the conductor (through the cross section of the conductor), in order to measure its magnitude, it is necessary to pass the measured current also through the ammeter. Therefore, the ammeter is included precisely in the break of the circuit under study, when it is necessary to measure the current, and in no case in parallel with it.The output circuit of a modern ammeter usually has a shunt...
To measure a variable or constant voltage in AC and DC circuits, a device called a voltmeter is used. Since voltage is present between different points of the circuit or at the poles of the voltage source, the voltmeter is always connected in parallel with the section of the circuit under study or in parallel with the terminals of the voltage source.You can, of course, turn on the voltmeter in series, in a circuit break, but then the source voltage will be measured, and not in the circuit section, since the circuit will be open, and the voltmeter itself will have a very large internal resistance ...
An LED lamp is a light source based on LEDs. LEDs are special semiconductor devices that are designed specifically to produce light when an electric current is passed through them. Unlike incandescent lamps, LED lamps have a higher efficiency. And while an incandescent lamp converts about 5-10% of the electrical energy supplied to it into light, an LED lamp has an efficiency of about 50%. In principle, LEDs are 10 times more luminous than incandescent lamps.LEDs require low voltage to power them...
The capacitor is designed for temporary storage of electrical energy in the form of potential energy of positive and negative electrical charges separated in space, that is, in the form of an electric field in the space between them. Accordingly, an electric capacitor includes three main components: two conductive plates, on which there are separated charges in a charged capacitor, and a dielectric layer located between the plates.Capacitor plates, depending on the type of this electrical product ...
Although not every substance can be used to make a permanent magnet, all substances are magnetized in one way or another when placed in an external magnetic field. Some of the substances are magnetized more strongly, and some are so weakly magnetized that this cannot be noticed without special instruments.When we say "matter has become magnetized", we mean the fact that the substance itself became a source of a magnetic field due to the influence of an external magnetic field. That is, the parameters of the magnetic induction vector B in the presence of this substance in a given space do not correspond to the magnetic induction vector...
At an equal temperature of metal conductors contacting in a closed circuit, the contact potential difference at the boundaries between them will not create any current in the circuit, it will only balance the oppositely directed electron flows.Having calculated the algebraic sum of the potential differences between the contacts, it is easy to understand that it vanishes. Therefore, in this case, there will be no EMF in the circuit. But what if the contact temperatures differ? Let's say contacts C and D will be at different temperatures. What then? Assume that the work function of electrons...
Let's do this thought experiment. Imagine that there is a certain village at a distance of 100 kilometers from the city, and that a wired signal line about 100 kilometers long with a light bulb at the end has been laid from the city to this village. The line is shielded two-wire, it is laid on supports along highway. And if we now send a signal along this line from the city to the countryside, then after what time can it be received there?Calculations and experience tell us that a signal in the form of a lit light bulb will appear ...
Everything that will be given in this lesson, it is necessary not only to read and remember some key points and 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. You can't 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 assessment 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. His number is enormous. 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 big 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 them they write RA, which means a current meter. The measuring device is designed for a current not exceeding a certain limit for this appliance. 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. For a unit electrical resistance adopted om (written by Om) - 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 1000000 Ohm, 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 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 to it is 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, about 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, then you get a complete circuit of a 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 greater 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, arising 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 light bulb from a round electric lamp, rated for a voltage of 2.5 V and a current of 0.075 A. Can this light 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. In 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 high, 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 1H, in which, when the current in it changes by 1 A, for 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, measured in thousandths of a henry, called a 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 so: 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, an electric flashlight bulb (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. 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.
Very few people understand the essence of electricity. Such concepts as "electric current", "voltage", "phase" and "zero" are a dark forest for the majority, although we encounter them every day. Let's get a grain of useful knowledge and figure out what a phase and zero in electricity are. To teach electricity from scratch, we need to understand the fundamental concepts. We are primarily interested in electric current and electric charge.
Electric current and electric charge
Electric charge is a physical scalar quantity that determines the ability of bodies to be a source of electromagnetic fields. The carrier of the smallest or elementary electric charge is an electron. Its charge is approximately -1.6 times 10 to the minus nineteenth power of Coulomb.
Electron charge - the minimum electric charge (quantum, portion of charge) that occurs in nature in free long-lived particles.
Charges are conditionally divided into positive and negative. For example, if we rub an ebonite stick on wool, it will acquire a negative electrical charge (an excess of electrons that were captured by the atoms of the stick upon contact with the wool).
The same nature has static electricity on the hair, only in this case the charge is positive (the hair loses electrons).
The main type of alternating current is sinusoidal current . This is such a current that first increases in one direction, reaching a maximum (amplitude) begins to decrease, at some point it becomes zero and rises again, but in a different direction.
Directly about the mysterious phase and zero
We all heard about the phase, three phases, zero and grounding.
The simplest case of an electrical circuit is single phase circuit . It has only three wires. On one of the wires, the current flows to the consumer (let it be an iron or a hair dryer), and on the other, it returns back. The third wire in a single-phase network is ground (or ground).
The ground wire does not carry a load, but serves as a kind of fuse. In case something gets out of hand, grounding helps prevent electric shock. Through this wire, excess electricity is diverted or "drains" into the ground.
The wire carrying current to the device is called phase , and the wire through which the current returns - zero.
So, why do we need zero in electricity? Yes, for the same as the phase! Through the phase wire, the current flows to the consumer, and through the zero wire, it is discharged in the opposite direction. The network through which the alternating current is distributed is three-phase. It consists of three phase wires and one reverse.
It is through such a network that the current goes to our apartments. Approaching directly to the consumer (apartments), the current is divided into phases, and each of the phases is given zero. The frequency of current direction change in the CIS countries is 50 Hz.
AT different countries there are different voltage and frequency standards in the network. For example, a typical household outlet in the United States is supplied with alternating current with a voltage of 100-127 volts and a frequency of 60 hertz.
The phase and zero wires must not be confused. Otherwise, you can arrange a short circuit in the circuit. To prevent this from happening and you do not confuse anything, the wires have acquired a different color.
What color are the phase and zero indicated in electricity? The zero is usually blue or cyan, while the phase is white, black, or brown. The ground wire also has its own color - yellow-green.
So, today we learned what the concepts of “phase” and “zero” mean in electricity. We will be just happy if this information was new and interesting for someone. Now, when you hear something about electricity, phase, zero and earth, you will already know what it is about. Finally, we remind you that if you suddenly need to calculate a three-phase AC circuit, you can safely contact student service. With the help of our specialists, even the wildest and difficult task will be "too tough" for you.
Faced with a situation where some electrical unit fails in the house, we immediately begin to look for a solution to this problem. It will be right to call a qualified professional who will quickly eliminate it. But many take up the work on their own, having no idea how it is done, they begin to pick, unwind, peer for a long time, trying to determine what is the reason. And having basic knowledge of electrics and with the right selection of tools, you can fix the problem efficiently and spend a minimum of time.
What a novice electrician needs to know
First of all, it is necessary not only to familiarize yourself, but to learn the safety rules. Electric current poses a strong threat to the human body and failure to comply with (TB) can lead to serious consequences.
There are two types of current effects on a person: electrical injury and electrical shock. The main injuries include burns, electrical signs, mechanical damage and electrometallization of the skin.
Need to know! Compliance with safety regulations and following the instructions significantly reduces the risk of accidents.
With an electric shock, the current passing through the human body causes maximum muscle contraction, which, with prolonged exposure, leads to clinical death.
Important rules:
- Before starting work, de-energize the network;
- Post a sign to warn of work in progress;
- Make sure the repair area is adequately lit;
- Check the availability of electricity with special devices;
- Use an insulated tool for the job.
Experienced advice: Touch the bare conductors only with the back of the hand, so that during an electric shock, the muscles, squeezing the brush into a fist, do not wrap around the wire, and it is possible to remove the hand from the contact.
Everything about electricity for a novice electrician: the basics
The use of electricity has become truly global. This includes lighting fixtures with fluorescent, neon and incandescent lamps. Appliances which is mainly powered by electricity.
Electric current is divided into two types: alternating, with a variable magnitude and direction of charged particles, and direct, with stable properties and direction.
Information and communication facilities such as telephones and computers. Electronic musical instruments. Electric current is used as a driving force for subway trains, trolleybuses and trams. Automotive electronics cannot do without current. Even nervous system human works on weak electrical impulses.
Electric current values:
- Current strength (measured in amperes);
- Voltage (measured in volts);
- Power (measured in watts);
- Frequency (measured in hertz).
Do not forget about the materials from which the current-carrying elements are made. Conductors - this group includes metals (copper, aluminum and silver), which have a high electrical conductivity.
Semiconductors - passing current or with high losses, or in one direction in the presence of certain factors (light, heat, electric or magnetic field).
Dielectrics are substances that do not conduct electricity.
Tools to help the electrician
It doesn’t matter if you are a master or a novice electrician, for work you should have a set of specialized tools that will help you cope with the task with high quality and much faster. Although there are a huge number of tools, they are divided into three groups.
Tool types:
- Hand tools;
- power tools;
- Measuring instruments.
Hand tools include: various mounting screwdrivers (flat and curly). Pliers, which not only bite the wires, but also connect the contacts into "twisting". Various mounting knives for stripping the insulation from the cable. Side cutters, with their help, it is easy to bite thicker veins. Crimping pliers, if sleeves are used to connect the contacts. Hammer and chisel.
When installing, always use only insulated tools, or insulate it yourself with electrical tape or heat shrink tubing.
The set of power tools includes:
- Perforator with various crowns and drills for wood and concrete;
- Screwdriver;
- Grinding machine (UShM) - "Bulgarian";
- Required measuring instruments: Multimeter and indicator screwdriver.
Do not forget to add electrical tape, tape measure, various heat shrinks, as well as a marker or pencil to this list.
Do not rush to throw away the failed extension cord. First you need to identify the cause of the breakdown, and if it is not serious, it can be repaired. There may be several reasons. For example, during the operation of the unit, one of the contacts in the plug oxidized or fell off, the integrity of the cable itself could be violated, or the contacts in the unit itself could be broken.
Most often, due to careless handling, the cable fails, which was either subjected to physical impact (dropped something heavy), or burns out, unable to withstand the load.
There are two ways to restore functionality. Connect the old cable with the help of “twisting”, or completely replace it. When replacing, some advantages appear - this, and the ability to select a section of a larger cable diameter and its length.
Required tools:
- pliers;
- Screwdriver Set;
- Stationery or mounting knife;
- Plug (provided that the old one is not collapsible).
And so, when the tool and materials are prepared, you can get to work. You need to start by dismantling the failed cable. To do this, unscrew the mounting bolts on the case by removing the top cover. Loosen the screws on the terminals and pull out the wire. Insert the cable prepared for replacement into the terminals and tighten the screws. Assemble the extension housing.
Note! Before starting installation or dismantling work, always check the presence of electric current in the conductor using specialized tools.
We do the same with the power plug. We disassemble, unscrewing the fixing bolts (or bolt), loosen the bolts on the terminals and pull out the wire. We insert a new cable into the terminals, clamp and assemble the plug in the reverse order.
That's all! Your extension cord is back in working order.
How to lay a cable in an apartment: wiring for dummies
Light switch - acts as a relay capable of forcibly closing and opening contacts. And in order to install it yourself, it is not necessary to be an electrician guru, just follow the instructions clearly and follow the safety rules.
Provided that the cable is laid and the hole for the socket is ready in the wall, you can proceed with the installation.
- Screwdriver Set;
- pliers;
- Stationery knife;
- Spatula (for installing the socket).
After making sure that there is no voltage in the network, we install the socket exactly along the plane of the wall, having previously inserted the wire, and cover the outer cavities with alabaster. We disassemble the switch, and on the inside of the mechanism we find contact terminals (marking L - incoming phase wire, arrow - outgoing).
The switch opens the phase contact, for ease of repair and operation.
According to the marking, we connect the wires to the mechanism, insert its socket box, align it horizontally and fix it with bolts. Set the frame and keys. Ready!
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