Without a certain initial knowledge of electricity, it’s hard to imagine how electrical appliances work, why they work at all, why you need to plug in the TV to make it work, and a small battery is enough for a flashlight to shine in the dark.
And so we will understand everything in order.
Electricity
Electricity is a natural phenomenon that confirms the existence, interaction and movement of electric charges. Electricity was first discovered as early as the 7th century BC. Greek philosopher Thales. Thales drew attention to the fact that if a piece of amber is rubbed against wool, it begins to attract light objects to itself. Amber in ancient Greek is electron.
This is how I imagine Thales sitting, rubbing a piece of amber on his himation (this is a woolen outerwear among the ancient Greeks), and then, with a puzzled look, looks at how hair, scraps of thread, feathers and scraps of paper are attracted to amber.
This phenomenon is called static electricity. You can repeat this experience. To do this, rub well woolen cloth a regular plastic ruler and bring it to the small pieces of paper.
It should be noted that this phenomenon has not been studied for a long time. And only in 1600, in his essay "On the Magnet, Magnetic Bodies, and the Great Magnet - the Earth", the English naturalist William Gilbert introduced the term - electricity. In his work, he described his experiments with electrified objects, and also established that other substances can become electrified.
Then, for three centuries, the most advanced scientists of the world have been exploring electricity, writing treatises, formulating laws, inventing electrical machines, and only in 1897, Joseph Thomson discovers the first material carrier of electricity - an electron, a particle, due to which electrical processes in substances are possible.
Electron is an elementary particle, has a negative charge approximately equal to -1.602 10 -19 Cl (Pendant). Denoted e or e -.
Voltage
To make charged particles move from one pole to another, it is necessary to create between the poles potential difference or - Voltage. Voltage unit - Volt (IN or V). In formulas and calculations, stress is indicated by the letter V . To get a voltage of 1 V, you need to transfer a charge of 1 C between the poles, while doing work of 1 J (Joule).
For clarity, imagine a tank of water located at a certain height. A pipe comes out of the tank. Water under natural pressure leaves the tank through a pipe. Let's agree that water is electric charge, the height of the water column (pressure) is voltage, and the water flow rate is electricity.
Thus, the more water in the tank, the higher the pressure. Similarly, from an electrical point of view, the greater the charge, the higher the voltage.
We begin to drain the water, while the pressure will decrease. Those. the charge level drops - the voltage value decreases. This phenomenon can be observed in a flashlight, the light bulb shines dimmer as the batteries run out. Note that the lower the water pressure (voltage), the lower the water flow (current).
Electricity
Electricity- this is a physical process of directed movement of charged particles under the influence of an electromagnetic field from one pole of a closed electrical circuit to another. Charge-transporting particles can be electrons, protons, ions, and holes. In the absence of a closed circuit, current is not possible. Particles capable of carrying electric charges do not exist in all substances, those in which they exist are called conductors And semiconductors. And substances in which there are no such particles - dielectrics.
Unit of measurement of current strength - Ampere (A). In formulas and calculations, the current strength is indicated by the letter I . A current of 1 Ampere is formed when a charge of 1 Coulomb (6.241 10 18 electrons) passes through a point in the electrical circuit in 1 second.
Let's go back to our water-electricity analogy. Only now let's take two tanks and fill them with an equal amount of water. The difference between the tanks is in the diameter of the outlet pipe.
Let's open the taps and make sure that the flow of water from the left tank is greater (the pipe diameter is larger) than from the right one. This experience is a clear proof of the dependence of the flow rate on the diameter of the pipe. Now let's try to equalize the two streams. To do this, add water to the right tank (charge). This will give more pressure(voltage) and increase the flow rate (current). In an electrical circuit, the pipe diameter is resistance.
The conducted experiments clearly demonstrate the relationship between voltage, current And resistance. We’ll talk more about resistance a little later, and now a few more words about the properties electric current.
If the voltage does not change its polarity, plus to minus, and the current flows in one direction, then this is D.C. and correspondingly constant pressure. If the voltage source changes its polarity and the current flows in one direction, then in the other - this is already alternating current And AC voltage. Maximum and minimum values (marked on the graph as io ) - This amplitude or peak currents. In household outlets, the voltage changes its polarity 50 times per second, i.e. the current oscillates back and forth, it turns out that the frequency of these oscillations is 50 Hertz, or 50 Hz for short. In some countries, such as the USA, the frequency is 60 Hz.
Resistance
Electrical resistance – physical quantity, which determines the property of the conductor to prevent (resist) the passage of current. Resistance unit - Ohm(denoted Ohm or the Greek letter omega Ω ). In formulas and calculations, resistance is indicated by the letter R . A conductor has a resistance of 1 ohm, to the poles of which a voltage of 1 V is applied and a current of 1 A flows.
Conductors conduct current differently. Their conductivity depends, first of all, on the material of the conductor, as well as on the cross section and length. The larger the cross section, the higher the conductivity, but the longer the length, the lower the conductivity. Resistance is the inverse of conduction.
On the example of a plumbing model, the resistance can be represented as the diameter of the pipe. The smaller it is, the worse the conductivity and the higher the resistance.
The resistance of the conductor is manifested, for example, in the heating of the conductor when current flows in it. Moreover, the greater the current and the smaller the cross section of the conductor, the stronger the heating.
Power
Electric power is a physical quantity that determines the rate of electricity conversion. For example, you have heard more than once: "a light bulb for so many watts." This is the power consumed by the light bulb per unit of time during operation, i.e. converting one form of energy into another at a certain rate.
Sources of electricity, such as generators, are also characterized by power, but already generated per unit of time.
Power unit - Watt(denoted Tue or W). In formulas and calculations, power is indicated by the letter P . For AC circuits, the term is used Full power , unit - Volt-ampere (V A or VA), denoted by the letter S .
And finally about electrical circuit. This circuit is a set of electrical components capable of conducting electric current and connected to each other in an appropriate way.
What we see in this image is an elementary electrical appliance (flashlight). under tension U(B) a source of electricity (batteries) through conductors and other components with different resistances 4.61 (244 Votes)
The unit of voltage is named volt (V) in honor of the Italian scientist Alessandro Volta, who created the first galvanic cell.
The unit of voltage is taken as the voltage at the ends of the conductor, in which the work of moving electric charge in 1 C along this conductor is equal to 1 J.
1 V = 1 J / C
In addition to the volt, submultiples and multiples of it are used: millivolt (mV) and kilovolt (kV).
1 mV = 0.001 V;
1 kV = 1000 V.
High (large) voltage is life-threatening. Assume that the voltage between one wire high voltage line transmission and earth 100,000 V. If this wire is connected by some conductor to earth, then when an electric charge of 1 C passes through it, work equal to 100,000 J will be done. Approximately the same work will be done by a load of 1000 kg when falling from a height 10 m. It can cause great destruction. This example shows why high voltage current is so dangerous.
Volta Alessandro (1745-1827)
An Italian physicist, one of the founders of the theory of electric current, created the first galvanic cell.
But care must be taken when working with lower voltages. Even a few tens of volts can be dangerous depending on conditions. For work indoors, a voltage of no more than 42 V is considered safe.
Galvanic cells create a low voltage. Therefore, the lighting network uses electric current from generators that create voltages of 127 and 220 V, that is, they produce much more energy.
Questions
- What is the unit of voltage?
- What voltage is used in the lighting network?
- What is the voltage at the poles of a dry cell and an acid battery?
- What units of voltage, other than the volt, are used in practice?
Hello everyone, Vladimir Vasiliev is in touch with you again. New Year's celebrations are coming to an end, which means you need to prepare for working days, with which I congratulate you, dear friends! Heh, just don't get upset and depressed, you need to think positively.
So, during these New Year holidays, I somehow thought about the audience of my blog: “Who is he? Who is the visitor to my blog that comes every day to read my posts? Maybe it's a well-rounded specialist who came in out of curiosity to read what I've done here? Or maybe it's some kind of doctor of radio engineering sciences who came to see how to solder a multivibrator circuit? 🙂
You know, all this is unlikely, because for an experienced specialist all this has already passed the stage and most likely everything is no longer so interesting and they themselves have a mustache. They may be interested only out of idle curiosity, of course I am very pleased and I am waiting for everyone with open arms.
So I came to the conclusion that the main contingent of my blog and most of the amateur radio sites are beginners and amateurs scouring the Internet in search of useful information. So what the hell, I have so little of it? It will be better soon so do not miss!
I remember myself when I searched the Internet for some simple scheme to start somewhere, but something always didn’t fit, something seemed abstruse. I lacked the basics, such that it was possible, according to the principle from simple to complex, to begin to understand the topic of interest to me.
By the way, the first book that really helped me, from reading which understanding really began to come, was the book “The Art of Circuitry” by P. Horowitz, W. Hill. I wrote about her in, there you can download the book. So, if you are a beginner, be sure to download it and let it become your reference book.
What is voltage and current?
By the way, what exactly is electric current and voltage? I think that no one really knows, because in order to know this one must at least see it. Who can see the current running through the wires?
Yes, no one, humanity has not yet achieved such technologies to personally observe the movement of electric charges. Everything that we see in textbooks and scientific papers is a kind of abstraction created as a result of numerous observations.
Well, you can talk a lot about this ... So let's try to figure out what electric current and voltage are. I will not write definitions, definitions do not give the very understanding of the essence. If interested, take any physics textbook.
Since we do not see the electric current and all the processes occurring in the conductor, then we will try to create an analogy.
And traditionally, the electric current flowing in the conductor is compared with water running through pipes. In our analogy, water is an electric current. Water runs through the pipes at a certain speed, the speed is the current strength, measured in amperes. Well, pipes are a conductor.
Well, we imagined the electric current, but what is voltage? Let's help now.
Water in the pipe, in the absence of any forces (gravity, pressure), will not flow, it will rest like any other liquid poured onto the floor. So this force or, more precisely, energy in our plumbing analogy will be the very tension.
But what happens to the water running from a reservoir located high above the ground? Water rushes in a stormy stream from the reservoir to the surface of the earth, driven by gravity. And the higher the tank is located from the ground, the faster water flows out of the hose. Do you understand what I'm talking about?
The higher the tank, the greater the force (read voltage) on the water. And so more speed water flow (read current strength). Now it becomes clear and a colorful picture begins to form in my head.
The concept of potential, potential difference
The concept of "potential" or "potential difference" is closely related to the concept of electric current voltage. Okay, back to our plumbing analogy.
Our tank is on a hill, which allows water to flow down the pipe unhindered. Since the water tank is at a height, the potential of this point will be higher or more positive than the one at ground level. See what happens?
We have two points with different potentials, more precisely different size potential.
It turns out that in order for an electric current to run through a wire, the potentials must not be equal. Current flows from a point of higher potential to a point of lower potential.
Remember this expression that the current runs from plus to minus. So this is all the same. Plus is more positive and minus is more negative.
By the way, do you want a backfill question? What will happen to the current if the potential values periodically change places?
Then we will observe how the electric current changes its direction to the opposite every time the potentials change. This will turn out to be alternating current. But we will not consider it yet, so that a clear understanding of the processes is formed in the head.
Voltage measurement
A voltmeter is used to measure voltage, although multimeters are now the most popular. A multimeter is such a combined instrument that has a lot of things in it. I wrote about it and told how to use it.
A voltmeter is just the device that measures the potential difference between two points. The voltage (potential difference) at any point in the circuit is usually measured relative to ZERO or GND or GROUND or MINUS of the battery. It does not matter, the main thing is that it should be the point with the lowest potential in the entire circuit.
So to measure voltage direct current between two points, do the following. The black (negative) probe of the voltmeter is stuck at the point where we can presumably observe a point with a lower potential (ZERO). We stick the red probe (positive) into the point whose potential is of interest to us.
And the result of the measurement will be the numerical value of the potential difference, or in other words, the voltage.
Current measurement
Unlike voltage, which is measured at two points, current is measured at one point. Since the current strength (or they simply say current) by our analogy is the speed of the flow of water, this speed needs to be measured only at one point.
We need to cut the water supply and insert a counter into the gap that will count liters and minutes. Something like this.
Similarly, if we return to the real world of our electrical model, we get the same thing. To measure the magnitude of the electric current, we need to connect a simple device, an ammeter, to the break in the electrical circuit. The ammeter is also part of the multimeter. You can also read in .
The probes of the multimeter must be rearranged in the current measurement mode. Then we have a bite of our conductor, and connect the wire pieces to the multimeter and voila - the current value will be shown on the multimeter screen.
Well, dear friends, I think that we did not waste time in vain. Having become acquainted with our plumbing models, a puzzle began to take shape in my head, an understanding began to form.
Well, let's try to check it on Ohm's law.
- I - current measured in Amperes (A);
- U-voltage measured in Volts (V);
- R-resistance measured in Ohms (Ohm)
Ohm told us that electric current is directly proportional to voltage and inversely proportional to resistance.
I didn’t talk about resistance today, but I think you understand. Resistance to electric current is the material of the conductor. In our plumbing system, the flow of water is resisted by rusty pipes clogged with rust and other things. 🙂
Thus, Ohm's law works in all its glory, both for the plumbing system and for the electric one. Maybe I should go into plumbing, there are a lot of similarities. 🙂
The higher the water tank is raised, the faster the water will flow through the pipes. But if the pipes are polluted, then the speed will be less. The greater the resistance to water, the slower it will flow. If there is a blockage, then the water can generally stand up.
Well, for electricity. The magnitude of the current is directly proportional to the magnitude of the voltage (potential difference), and inversely proportional to the resistance.
The higher the voltage, the greater the current, but the greater the resistance, the lower the current. The voltage may be very high, but the current may not flow due to a break. And a break is the same as if instead of a metal conductor we connected a conductor made of air, and the air has just a gigantic resistance. This is where the current stops.
Well, dear friends, now it’s time to wrap up, like everything I wanted to say in this article I said. If you have any questions please ask in the comments. There will be more to come, I plan to write a series of tutorials, so do not miss…
I wish you good luck, success and see you soon!
From n/a Vladimir Vasiliev.
P.S. Friends, be sure to subscribe to updates! By subscribing you will receive new content directly to your inbox! And by the way, each subscriber will receive a useful gift!
Constructor ZNATOK 320-Znat "320 schemes" is a tool that will allow you to gain knowledge in the field of electronics and electrical engineering, as well as to achieve an understanding of the processes occurring in conductors.
The constructor is a set of full-fledged radio components with special. constructive, allowing their installation without the help of a soldering iron. The radio components are mounted on a special board - the base, which ultimately allows you to get fully functional radio structures.
Using this constructor, you can assemble up to 320 different schemes, for the construction of which there is a detailed and colorful guide. And if you connect your imagination to this creative process, you can get countless different radio structures and learn how to analyze their work. I consider this experience very important and for many it can be invaluable.
Here are some examples of what you can do with this constructor:
Flying propeller;
A lamp turned on by clapping your hands or a jet of air;
Controlled Sounds star wars, fire truck or ambulance;
Music fan;
Electric light gun;
Learning Morse code;
Lie detector;
Automatic street lamp;
Megaphone;
radio station;
Electronic metronome;
Radio receivers, including FM range;
A device that reminds of the onset of darkness or dawn;
Alarm that the child is wet;
Security alarm;
Musical door lock;
Lamps in parallel and series connection;
Resistor as current limiter;
Capacitor charge and discharge;
Conductivity tester;
Amplifying effect of the transistor;
Diagram of Darlington.
P.S. We have a kind of redneck here - the greedy will not notice the social button, and the generous one shares with friends. 🙂
One of the physical quantities that was introduced to characterize the action electric field, is the voltage. An electric field exerts a force on charged particles, sets them in motion, and creates an electric current. When charges move, work is done, which leads to a change in energy.
What unit is voltage measured in?
The ratio of the work done by an arbitrary electric field when moving a positive charge from one point of the field to another, to the magnitude of the charge is called the voltage between these points:
$ U = ( A\over q ) $ (1)
U- voltage,
A— work, J,
q- charge, Cl.
So the work of the electric field when moving the charge is equal to the product of the voltage U between points per charge q:
$ A = ( q*U ) $ (2)
Rice. 1. The work of the electric field on the movement of charges.
With a charge equal to 1 C, the equality $ U = A $ will be fulfilled.
The unit of measure for voltage is called the volt. In short spelling, it is written with a capital letter B. The unit got its name in honor of the Italian scientist Alessandro Volta (1745-1827), who made a significant contribution to understanding the nature of electrical phenomena.
From considerations of the dimension of quantities and formula (1), it follows that:
$$ [V] = ( [J]\over ) $$
Thus, a unit of voltage (1 Volt) is such a voltage at a section of a circuit or at the ends of a conductor at which work is done to move an electric charge of 1 C (1 coulomb) equal to 1 J (1 Joule).
Multiple units of voltage measurement
The real values of the measured voltages can be tens of thousands of times more or less than one volt. Therefore, for the convenience of recording (fixing), the following multiple and submultiple units were additionally introduced:
- 1 nanovolt - 1 nV \u003d 10 -9 V;
- 1 microvolt - 1 μV \u003d 10 -6 V;
- 1 millivolt - 1 mV \u003d 10 -3 V;
- 1 kilovolt - 1 kV \u003d 10 3 V;
- 1 megavolt - 1 MV \u003d 10 6 V.
It must be remembered that high voltage is a great danger to human health. A voltage of 42 V under normal conditions and 12 V under conditions with increased danger (humidity, metal floors, high temperature) is considered a safe value for the human body.
How voltage is measured
Voltage is measured using a device called a voltmeter. Different models of voltmeters may look different from each other, but the common principle for them is the principle of operation, based on the electromagnetic action of the current. The Latin letter V is used to designate a device on electrical diagrams and on the measuring scales of voltmeters.
Rice. 2. The designation of the voltmeter and the connection diagram of the voltmeter for measuring voltage.
When taking measurements, the following points must be taken into account:
- Voltmeters for measuring DC voltage are different from voltmeters for measuring AC voltage. For voltmeters for measuring direct voltages, the “-” sign must be present on the measuring scale, and for alternating voltage, the “~” sign. IN Lately often used designation using abbreviations of letters English alphabet AC/DC (Alternative Current - alternating current, Direct Current - direct current);
- Voltmeter terminals for direct voltage are marked with “+” and “-” signs or highlighted in color (plus - red, minus - blue). When measuring, polarity must be observed, otherwise the indicator arrow will deviate in the other direction;
- The voltmeter is always connected in parallel to the section of the circuit where measurements are made;
- It is recommended that you first install all the elements of the electrical circuit, and connect the voltmeter at the very end.
Rice. 3. Examples of various voltmeters
All measuring devices should not affect the measurement result, that is, they should have a minimum measurement error. To meet this requirement, voltmeters have a very large input impedance, so the current flowing through them is much less than the current in the measured section of the circuit. Then the voltage drop across the voltmeter becomes insignificant.
What have we learned?
So, we learned that voltage is a physical quantity equal to the work of moving a charge of 1 C in an electric field. Voltage is measured in units called volts. Voltmeters are used to measure voltage.
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In fact, this term refers to the potential difference, and the unit of voltage is the volt. Volt is the name of the scientist who laid the foundation for everything we now know about electricity. This man's name was Alessandro.
But this is what concerns the electric current, i.e. the one with which the household electrical appliances familiar to us work. But there is also the concept of a mechanical parameter. A similar parameter is measured in pascals. But now it's not about him.
What is a volt
This parameter can be either constant or variable. Just alternating current “flows” into apartments, buildings and structures, houses and organizations. Electric voltage is an amplitude wave, indicated on the graphs as a sinusoid.
Alternating current is indicated in the diagrams by the symbol "~". And if we talk about what one volt is equal to, then we can say that this is an electrical action in a circuit where, when a charge equal to one pendant (C) flows, work equal to one joule (J) is performed.
The standard formula by which it can be calculated is:
U = A:q, where U is exactly the required value; "A" is the work that is done electric field(in J), transferring a charge, but “q” is just the charge itself, in pendants.
If we talk about constant values, then they practically do not differ from variables (with the exception of the construction schedule) and are also produced from them by means of a rectifier diode bridge. Diodes, without passing current in one of the directions, divide the sinusoid, as it were, removing half-waves from it. As a result, instead of phase and zero, plus and minus are obtained, but the calculation remains in the same volts (V or V).
Voltage measurement
Previously, only an analog voltmeter was used to measure this parameter. Now on the shelves of electrical stores there is a very wide range of such devices already in digital form, as well as multimeters, both analog and digital, with which the so-called voltage is measured. Such a device can measure not only the magnitude, but also the strength of the current, the resistance of the circuit, and even it becomes possible to check the capacitance of the capacitor or measure the temperature.
Of course, analog voltmeters and multimeters do not give such accuracy as digital ones, on the display of which the unit of voltage is displayed up to hundredths or thousandths.
When measuring this parameter, the voltmeter is connected to the circuit in parallel, i.e. if necessary, measure the value between phase and zero, the probes are applied one to the first wire, and the other to the second, in contrast to measuring the current strength, where the device is connected to the circuit in series.
In the circuits, the voltmeter is denoted by the letter V, circled. Various types such devices measure, in addition to the volt, different units of voltage. In general, it is measured in the following units: millivolt, microvolt, kilovolt or megavolt.
Voltage value
The value of this electric current parameter in our life is very high, because it depends on whether it corresponds to the prescribed one, how brightly the incandescent lamps will burn in the apartment, and if compact fluorescent lamps are installed, then the question already arises whether they will burn at all or not. The durability of all lighting and household electrical appliances depends on its jumps, and therefore the presence of a voltmeter or multimeter at home, as well as the ability to use it, becomes a necessity in our time.
