Before proceeding with work related to electricity, it is necessary to “be a little savvy” theoretically in this matter. Simply put, electricity is usually understood to mean this movement of electrons under the influence of an electromagnetic field. The main thing is to understand that electricity is the energy of the smallest charged particles that move inside the conductors in a certain direction.
D.C practically does not change its direction and magnitude in time. Suppose a regular battery has a constant current. Then the charge will flow from minus to plus, without changing, until it runs out.
Alternating current is a current that changes direction of movement and magnitude with a certain periodicity.
Imagine the current as a stream of water flowing through a pipe. After a certain period of time (for example, 5 s), water will rush either one way or the other. With current, this happens much faster - 50 times per second (frequency 50 Hz). During one oscillation period, the current rises to a maximum, then passes through zero, and then the reverse process occurs, but with a different sign. When asked why this happens and why such a current is needed, it can be answered that receiving and transmitting alternating current is much simpler than direct current.
Receiving and transmitting AC is closely related to a device such as a transformer. A generator that produces alternating current is much simpler in a device than a direct current generator. In addition, alternating current is best suited for transmitting energy over a long distance. With it, less energy is lost.
Using a transformer (a special device in the form of coils), alternating current is converted from low voltage to high and vice versa, as shown in the illustration. It is for this reason that most devices operate from a network in which the current is alternating. However, direct current is also widely used - in all types of batteries, in the chemical industry and some other areas.
Many have heard such mysterious words as one phase, three phases, zero, ground or earth, and they know that these are important concepts in the world of electricity. However, not everyone understands what they mean and how they relate to the surrounding reality. Nevertheless, you must know this. Without going into technical details that a homemaster does not need, we can say that a three-phase network is such a method of transmitting electric current when alternating current flows through three wires, and one back. The above should be clarified a bit. Any electrical circuit consists of two wires. One current flows to the consumer (for example, to the kettle), and the other returns back. If you open such a circuit, then the current will not go. That's the whole description of a single-phase circuit.
The wire through which the current flows is called phase, or simply phase, and through which it returns - zero or zero. A three-phase circuit consists of three phase wires and one reverse. This is possible because the alternating current phase in each of the three wires is 120 ° C relative to the adjacent one. More details on this question will help answer the textbook on electromechanics. Transmission of alternating current occurs precisely with the help of three-phase networks. It is economically beneficial - two more neutral wires are not needed.
Approaching the consumer, the current is divided into three phases, and each of them is given zero. So he gets into apartments and houses. Although sometimes a three-phase network starts right in the house. As a rule, we are talking about the private sector, and this state of affairs has its pros and cons. This will be discussed later. Earth, or, more correctly, grounding is the third wire in a single-phase network. In essence, he does not carry a workload, but serves as a kind of safety lock. This can be explained by example. If the electricity goes out of control (for example, a short circuit), there is a danger of fire or electric shock. To prevent this from happening (that is, the current value should not exceed the level safe for humans and devices), grounding is introduced. Through this wire, an excess of electricity literally goes into the ground.
One more example. Suppose a small breakdown occurs in the operation of the electric motor of the washing machine and part of the electric current enters the outer metal shell of the appliance. If there is no ground, this charge will wander around the washing machine. When a person touches it, it will instantly become the most convenient outlet for a given energy, that is, it will receive an electric shock. If there is a ground wire in this situation, an excess charge will drain through it without causing any harm to anyone. In addition, we can say that the neutral conductor can also be a ground and, in principle, it is, but only at a power plant. The situation when the house does not have grounding is unsafe. How to cope with it without changing all the wiring in the house will be described in the future.
Attention!
Some craftsmen, relying on initial knowledge of electrical engineering, install a neutral wire as a ground wire. Never do that. If the neutral wire breaks off the case of the grounded devices will be under voltage 220 V.
In everyday life, we are constantly dealing with electricity. Without moving charged particles, the functioning of the instruments and devices we use is impossible. And in order to fully enjoy these achievements of civilization and ensure their long-term service, one must know and understand the principle of work.
Electrical Engineering is an Important Science
The questions related to the generation and use of current energy for practical purposes are answered by electrical engineering. However, to describe in an accessible language an invisible world where current and voltage reign, is not at all easy. therefore benefits are always in demand "Electricity for Dummies" or "Electrical Engineering for Beginners."
What is studying this mysterious science, what knowledge and skills can be obtained as a result of its development?
Description of the discipline "Theoretical foundations of electrical engineering"
In the student’s student’s grades, the mysterious abbreviation “TOE” can be seen. This is precisely the science we need.
The date of birth of electrical engineering can be considered the period of the beginning of the XIX century, when the first direct current source was invented. Physics became the mother of the “newborn” branch of knowledge. Subsequent discoveries in the field of electricity and magnetism enriched this science with new facts and concepts that had important practical value.
It took its modern form as an independent industry at the end of the 19th century, and since then part of the curriculum of technical universities and actively interacts with other disciplines. So, for a successful study of electrical engineering, it is necessary to have a theoretical body of knowledge from a school course in physics, chemistry and mathematics. In turn, important disciplines are based on TOE:
- electronics and radio electronics;
- electromechanics;
- power engineering, lighting engineering, etc.
The central focus of electrical engineering is, of course, current and its characteristics. Further, the theory talks about electromagnetic fields, their properties and practical applications. In the final part of the discipline, devices in which energetic electronicians work are highlighted. Having mastered this science a lot will understand in the world around.
What is the significance of electrical engineering in our time? Without knowledge of this discipline, electrical workers can not do:
- electrician;
- installer;
- energy.
The ubiquity of electricity makes its study necessary and simple for the average man to be a competent person and be able to apply his knowledge in everyday life.
It is difficult to understand what you cannot see and “feel”. Most electrical textbooks are full of obscure terms and cumbersome circuits. Therefore, the good intentions of beginners to study this science often remain only plans.
In fact, electrical engineering is a very interesting science, and the main provisions of electricity can be stated in an accessible language for dummies. If you approach the educational process creatively and with due diligence, much will become clear and fascinating. Here are some useful tips for studying electrics for dummies.
Journey to the World of Electrons you need to start by studying the theoretical foundations - concepts and laws. Get a training manual, for example, "Electrical Engineering for Dummies", which will be written in a language that is understandable to you, or several such textbooks. The presence of illustrative examples and historical facts will diversify the learning process and help to better absorb knowledge. You can check your progress with the help of various tests, tasks and exam questions. Return again to those paragraphs in which errors were made during the verification.
If you are sure that you have fully studied the physical section of the discipline, you can move on to more complex material - a description of electrical circuits and devices.
Feel quite savvy in theory? The time has come to develop practical skills. Materials for creating the simplest schemes and mechanisms can be easily found in stores of electrical and household goods. However, do not rush to start modeling immediately - Learn the “electrical safety” section first so as not to harm your health.
To get practical benefits from newfound knowledge, try to repair broken household appliances. Be sure to study the operating requirements, follow the instructions or invite an experienced electrician to work with you. The time of experiments has not come yet, and jokes are bad with electricity.
Try, do not rush, be inquisitive and assiduous, study all available materials and then from the “dark horse” electric current will turn into a good and faithful friend for you. And maybe you can even make an important discovery in the field of electrics and become rich and famous overnight.
Today, the transmission of electric energy to a distance is always performed at an increased voltage, which is measured in tens and hundreds of kilovolts. Various types of power plants around the world generate electricity in gigawatts. This electricity is distributed to cities and villages with the help of wires, which we can see, for example, along highways and railways, where they are invariably fixed on high poles with long insulators. But why is transmission always carried out at high voltage? We will talk about this further ...
In the traditional sense, alternating current is the current obtained due to alternating, harmonically changing (sinusoidal) voltage. Alternating voltage is generated at the power plant, and is constantly present in any wall outlet.It is precisely alternating current that is also used to transmit electricity over long distances, since the alternating voltage is easily increased with a transformer, and thus electric energy can be transmitted over a distance with minimal losses, and then reduced back ...
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Metals are excellent conductors of electric current. They conduct electric current, because they have free carriers of electric charge - free electrons. And if at the ends, for example, a copper wire, a potential difference is created using a constant EMF source, then an electric current will appear in such a conductor - the electrons will come in translational motion from the negative terminal of the EMF source to its positive terminal.Dielectrics, on the contrary, are not conductors of electric current, since there are no free carriers inside them ...
The magnet found its first practical use in the form of a piece of magnetized steel floating on a cork in water or oil. In this case, the magnet always points north at one end, and south at the other. It was the first compass used by sailors.Just a long time ago, several centuries before our era, people knew that resinous substance - amber, if rubbed with wool, gains the ability to attract light objects for a while: pieces of paper, pieces of thread, fluffs. This phenomenon has been called electric. It was later observed that electrified by friction ...
To answer the question “why does the dielectric not conduct electric current?”, First, let us recall what is electric current, and also call the conditions, the observance of which is necessary for the emergence and existence of electric current. And after that, we compare how conductors and dielectrics behave in relation to the search for an answer to this question.An electric current is an ordered, that is, directed, movement of charged particles under the influence of an electric field. Thus, firstly, the existence of an electric current requires the presence of free charged particles ...
The concept of energy is used in all sciences. It is also known that energy-rich bodies can do the work. The law of conservation of energy says that energy does not disappear and cannot be created from nothing, but appears in its various forms (for example, in the form of thermal, mechanical, light, electric energy, etc.).One form of energy can pass into another, and at the same time exact quantitative ratios of various types of energy are observed. Generally speaking, the transition of one form of energy to another never happens completely ...
Today there is not a single field of technology where, in one form or another, electricity would not be used. Meanwhile, the type of current supplying them is associated with the requirements for electrical devices. And although alternating current is very widespread today around the world, there are nevertheless areas where you just can not do without direct current. The first sources of usable direct current were galvanic cells, which essentially gave direct current chemicallyrepresenting a stream of electrons ...
Electricity today is defined as "electric charges and associated electromagnetic fields." The very existence of electric charges is detected through their force on other charges. The space around any charge has special properties: electric forces act in it, which appear when other charges are introduced into this space. Such a space is a power electric field.While the charges are motionless, the space between them has the properties of an electric (electrostatic) field ...
Nontrivial occupation, I tell you. :) In order to facilitate the assimilation of the material, I introduced a number of simplifications. Completely delusional and unscientific, but more or less clearly showing the essence of the process. The technique of "sewer electrics" has successfully proved itself in field trials, and therefore will be used here. I just want to draw attention to the fact that this is just a visual simplification, valid for the general case and for a specific moment, in order to understand the essence and has practically nothing to do with the real physics of the process. Why is it then? And to make it easier to remember that there’s no reason to confuse voltage and current and understand how resistance affects all this, otherwise I heard enough from students ...
Current, voltage, resistance.
If we compare the circuit with sewage, the power source is a drain tank, flowing water is current, water pressure is voltage, and shit rushing through the pipes is a payload. The higher the drain tank, the greater the potential energy of the water in it, and the stronger the pressure-current passing through the pipes will be, which means it will be able to flush more crap-load.
In addition to the current crap, the flow is prevented by friction against the pipe walls, forming losses. The thicker the pipe, the less loss (gee gee gee now you remember why audiophiles for their powerful acoustics take thicker wires;)).
So to summarize. The circuit contains a source that creates a potential difference between its poles - voltage. Under the influence of this voltage, the current rushes through the load to where the potential is lower. The movement of current is impeded by the resistance formed from the payload and losses. As a result, the voltage-pressure weakens the stronger, the greater the resistance. Well, now, let’s put our sewers in a mathematical direction.
Ohm's law
For example, let's calculate the simplest circuit, consisting of three resistances and one source. I will draw the circuit not as is customary in textbooks on SOE, but closer to the real circuit, where they take the point of zero potential - the case, usually equal to the minus power supply, and consider the plus point as a potential with a voltage equal to the voltage. To begin with, we believe that we know the voltage and resistance, which means we need to find the current. Add all the resistances (read the inset for the rules for adding resistances) in order to get the total load and divide the voltage by the result - the current is found! Now let's see how the voltage is distributed across each of the resistances. We turn Ohm's law inside out and begin to calculate. U \u003d I * R since the current in the circuit is the same for all series resistances, it will be constant, but the resistances are different. The result was that U source \u003d U1 + U2 + U3. Based on this principle, it is possible, for example, to connect in series 50 bulbs rated for 4.5 volts and quietly power from a 220 volt outlet - not a single bulb will burn out. And what will happen if one hefty resistance is put into this bundle, in the middle, let's say KiloOhm, and take the other two less - by one Ohm? And from the calculations it will become clear that almost all the voltage will drop out at this large resistance.
Kirchhoff's Law.
According to this law, the sum of the currents entering and leaving the node is equal to zero, and the currents flowing into the node are usually denoted with a plus, and flowing with a minus. By analogy with our sewer, water from one powerful pipe scatters along small heaps. This rule allows you to calculate the approximate current consumption, which is sometimes just necessary when calculating circuit diagrams.
Power and loss
The power that is consumed in the circuit is expressed as the product of voltage by current.
P \u003d U * I
Because the greater the current or voltage, the greater the power. Because the resistor (or wires) does not fulfill any payload, then the power falling out of it is pure losses. In this case, power can be expressed through the Ohm law as follows:
P \u003d R * I 2
As you can see, an increase in resistance causes an increase in power, which is spent on losses, and if the current increases, then the losses increase in a quadratic dependence. In the resistor, all the power goes into heating. For the same reason, by the way, batteries heat up during operation - they also have internal resistance, on which part of the energy is dissipated.
That's why audiophiles for their heavy-duty sound systems take thick copper wires with minimal resistance to reduce power losses, since there are considerable currents there.
There is a law of the total current in the circuit, although in practice it never came in handy for me, but it doesn’t hurt to know, so pulling out a textbook on TOE (theoretical fundamentals of electrical engineering) from the network is better for secondary schools, everything is much simpler and more understandable there - without going to higher mathematics.
Video version of the article:
Let's start with the concept of electricity. An electric current is an ordered movement of charged particles under the influence of an electric field. Particles can be free electrons of a metal if the current flows through a metal wire, or ions if the current flows in a gas or liquid.
There is still current in semiconductors, but this is a separate topic for conversation. As an example, you can cite a high-voltage transformer from a microwave - first the electrons run through the wires, then the ions move between the wires, so first the current goes through the metal, and then through the air. A substance is called a conductor or semiconductor if it contains particles that can carry 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 electric charge, which is measured by q in pendants. 
The unit of measurement of current is called Ampere and is denoted by beech I, a current of 1 Ampere is formed when a charge passes through a point of an electric circuit with a value of 1 Coulomb per 1 second, that is, roughly speaking, the current strength is measured in pendants a 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 running through the wire, the correspondingly greater the current.
To make charged particles move from one pole to another, it is necessary to create a potential difference between the poles or - Voltage. The voltage is measured in volts and is denoted by the letter V or U. In order to get a voltage of 1 volt, you need to transfer a charge of 1 C between the poles, while doing 1 J work. I agree, it’s a little incomprehensible. 
For clarity, imagine a reservoir of water located at a certain height. A pipe comes out of the tank. Water by gravity flows through a pipe. Let water be an electric charge, the height of the water column is voltage, and the flow rate of water is electric current. More precisely, not the flow rate, but the amount of water flowing 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 through the pipe, because the speed will be higher .. Similarly, the higher the voltage, the greater the current will flow in the circuit. 
The relationship between all three considered values \u200b\u200bin the DC circuit determines the Ohm law, which is expressed by this formula, and it sounds like the current strength in the circuit is directly proportional to the voltage, and inversely proportional to the resistance. The greater the resistance, the less current, and vice versa. 
Add a few words about resistance. It can be measured, but can be counted. Suppose we have a conductor having a known length and cross-sectional area. Square, round, it doesn’t matter. Different substances have different resistivity, and for our imaginary conductor there is such a formula that defines the relationship between length, cross-sectional area and resistivity. The resistivity of substances can be found on the Internet in the form of tables. 
We 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 time. See how simple it is? You don’t even need to remember 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 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’ll measure the same piece using the device. For such a small resistance, I have to subtract the resistance of the probes of my device, which is equal to 0.8 Ohms. Here it is!
The multimeter scale is divided by the size of the measured values, this is done for higher measurement accuracy. If I want to measure a resistor with a nominal value of 100 kOhm, I put the handle on the larger nearest resistance. In my case, it is 200 kilograms. If I want to measure 1 kilo, then I put it on 2 com. This is true for measuring the remaining quantities. That is, the scale limits the measurement to which you need to fall.
Let's continue to have fun with the multimeter and try to measure the rest of the studied values. I will take several different sources of direct current. Let it be a 12 volt power supply, USB port and a transformer, which my grandfather did 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 voltage everything is clear, it can be taken and measured. But in order to measure the strength of the current, you need to create an electrical circuit through which current will flow. The electric circuit must necessarily have a consumer, or a load. Let's connect the 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, switch the multimeter to the current measurement mode and switch the probe to the current input. The ammeter is connected to the circuit in series with the measured object. Here is the circuit, it should also be remembered and not confused with the connection of a voltmeter. By the way, there is such a thing as current clamps. They allow you to measure the current strength in the 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. Well, back to our usual ammeter. 
So, I measured all the currents. Now we know what current is consumed in each circuit. Here, the LEDs are on, the motor is spinning here, and here ... So stand, but what does a resistor do? He does not sing songs to us, does not light the room and does not rotate any mechanism. So what does he spend as much as 90 milliamps? It won’t work, let's understand. Hey you! Aw, he's hot! So that's where the energy is spent! Is it possible to somehow calculate what kind of energy is here? It turns out - you can. The law describing the thermal effect of electric current was discovered in the 19th century by two scientists, James Joule and Emil Lentz. 
The law was called the law of the Joule of Lenz. It is expressed by this formula, and numerically shows how many joules of energy are released in the conductor in which the current flows per unit time. From this law, you can find the power that is allocated on this conductor, the power is indicated by the English letter P and measured in watts. I found this very cool plate that links all the quantities that we have studied at this moment.
Thus, on my desk, 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, etc. work. Everywhere there is a thin spiral that heats up under the influence of current. 
This point should be taken into account when connecting wires to the load, that is, wiring to outlets in the apartment is also included in this concept. If you take a wire that is too thin to lead to a power outlet and connect a computer, kettle and microwave to this power outlet, the wire may become hot until a fire occurs. Therefore, there is such a plate that connects the cross-sectional area of \u200b\u200bthe wires with the maximum power that will go along these wires. If you decide to pull the wires - do not forget about it. 
Also in the framework of this issue, I would like to recall the features of parallel and serial 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 the consumers is the sum of all resistances. With a parallel connection, the voltage across all consumers is the same, the current strength is divided, and the total resistance is calculated using this formula.
One very interesting point that can be used to measure current strength follows from this. Suppose you want to measure the current strength in a circuit of about 2 amperes. The ammeter does not cope with this task, so you can use the Ohm 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. We measure the voltage on it. Now, using the law of ohm, we find the strength of the current. 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 the 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, 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 recall 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 enormous values, this is called a short circuit. If you remember the beginning of the release, then you can draw an analogy with water. If we substitute the zero resistance in the Ohm's law, then we get an infinitely large current. In practice, this of course does not happen, because the source has an internal resistance that is connected in series. This law is called Ohm's law for the complete chain. 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 determines the current in the circuit. Many wrote to me and asked me about this question, I’m exaggerating it a bit: Sanya, I have a power supply unit with 12 volts and 50 amperes. If I connect a small piece of LED strip to it, will it not burn? No, of course it will not burn. 50 amperes is the maximum current that a source is capable of delivering. If you connect a piece of tape to it, it will take its own, let's say 100 milliamps, that's all. The current in the circuit will be 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, 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 give a maximum of 2 amperes, and when I short-circuit it onto 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 that can give out tens of amperes, this situation will not appeal to a bolt. 
For example, let's calculate the power supply, which is required to power a known segment of an LED strip. So, we bought a reel of LED strip from the Chinese and we want to power three meters of this strip. First, 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. We look at 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 power so that it does not work in critical mode. As a result, we get 55 watts. The closest suitable power supply will be at 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, find, buy.
It is very important to know the current consumption in the manufacture of all kinds of 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 \u200b\u200belectricity is considered harmless to human life. 