Voltage in physics Unit of measurement. Electrical current measurement: voltage

The measurement of voltage in practice has to be performed quite often. The voltage is measured in radio engineering, electrical devices and chains, etc. View alternating current It may be impulse or sinusoidal. Voltage sources are or current generators.

Pulse current voltage has amplitude and medium voltage parameters. Sources of such a voltage can be pulsed generators. The voltage is measured in volts, has the designation "B" or "V". If the voltage is variable, then the symbol is set to " ~ "The constant voltage indicates the symbol" - ". AC voltage in the home household network label ~ 220 V.

These are devices designed to measure and control the characteristics of electrical signals. Oscilloscopes work on the principle of deviations of the electron beam, which gives the image of values \u200b\u200bof variables on the display.

AC voltage measurement

According to regulatory documents, the voltage in the household network must be equal to 220 volts with an accuracy of 10% deviations, that is, the voltage may vary in the 198-242 volt interval. If the lighting has become more dim in your home, the lamps began to fail, or the household devices began to work unstable, then to find out and eliminate these problems, it is necessary to measure the voltage in the network.

Before measuring, you should prepare the existing measuring instrument to work:

• Check the integrity of the insulation of control wires with affairs and tips.
• Set the switch to alternating voltage, with the upper limit of 250 volts or higher.
• Insert the tips of the control wires into the measuring instrument jacks, for example. In order not to make a mistake, it is better to look at the designation of the nests on the case.
• Turn on the device.

From the figure it is clear that the tester selected the measurement boundary of 300 volts, and at the 700 volt multimeter. Some devices require to measure the voltage to set several different switches to the desired position: Type of current, measurement type, and insert wire tips into certain sockets. The end of the black tip in the multimeter is stuck in the Nest of Som (general nest), the red tip is inserted into the socket with the designation "V". This socket is common to measure any type of voltage. The labeling socket "MA" is used for measurements of small currents. The nest with the designation "10 A" is used to measure a significant amount of current, which can reach 10 amps.

If you measure the voltage with the inserted wire into the "10 A" socket, the device fails, or burn the fuse. Therefore, when performing measuring work should be attentive. Most often errors occur in cases where they first measured the resistance, and then, forgetting to switch to another mode, the voltage is started. In this case, inside the device burns the resistor responsible for measuring the resistance.

After preparing the device, you can start measurements. If, when you turn on the multimeter, nothing appears on the indicator, it means that the battery, located inside the instrument, served its time and requires replacement. Most often in multimeters there is a "crown", outstanding 9 volts voltage. The service life is about a year, depending on the manufacturer. If you didn't use the multimeter for a long time, the crown can still be faulty. If the battery is working, the multimeter should show the unit.

Cups of the wires must be inserted into the outlet or touch them to bare wires.

The multimeter display immediately appears the voltage value of the network in digital video. On the arrow device, the arrow will deflex on some angle. The arrow tester has several graded scales. If they carefully consider them, then everything becomes clear. Each scale is intended for certain measurements: current, voltage or resistance.

The measurement boundary on the device was exhibited by 300 volts, so it is necessary to count on a second scale having limit 3, while the instrument readings must be multiplied by 100. The scale has a fission price of 0.1 volts, so we obtain the result depicted in the figure, about 235 volts. This result is within acceptable limits. If the instrument readings are constantly changing, possibly poor contact in electrical wiring connections, which can result in sincerity and malfunctions on the network.

Measurement of constant voltage

Sources of constant voltage are batteries, low-voltage or batteries, the voltage of which is no more than 24 volts. Therefore, touching the poles of the battery is not dangerous, and there is no need for special safety measures.

To assess the performance of the battery or other source, it is necessary to measure the voltage on its poles. In finger batteries, the poles of food are located on the ends of the case. Positive pole marked "+".

Permanent current is measured in a similar way, as well as variable. The difference is only in setting the instrument to the appropriate mode and compliance with the polarity of the conclusions.

The battery voltage is usually designated on the housing. But the measurement result does not yet indicate the serviceability of the battery, since the electromotive power of the batteries is measured. The duration of the operation of the device in which the power element will be installed depends on its container.

To accurately assess the performance of the battery, it is necessary to measure the voltage when the load is connected. For finger-batteries A regular light bulb for a 1.5 volt flashlight is suitable as a load. If the voltage at the light bulb is inclised slightly, that is, no more than 15%, therefore, the battery is suitable for work. If the voltage falls much stronger, then such a battery can still serve only in wall clocks that spend very little energy.

The voltage unit is called Volt (B) in honor of the Italian scientist Alessandro Volta, which created the first galvanic element.

The voltage unit takes such an electrical voltage at the ends of the conductor, in which the work on the movement of the electrical charge in 1 cl along this conductor is 1 J.

1 B \u003d 1 J / CL

In addition to the Volta, the Dolly and multiple units are used: Millivolt (MV) and kilovolt (KV).

1 mV \u003d 0.001 V;
1 kV \u003d 1000 V.

High (large) tension is dangerous for life. Suppose that the voltage between one wire of the high-voltage line of the transmission and the ground is 100,000 V. If this wire is combined with some conductor with the ground, then when it passes through it, an electric charge in 1 CL will work, equal to 100,000 J. Approximately the same work Make a load weighing 1000 kg when dropping from a height of 10 m. It can produce great destruction. This example shows why the high voltage current is so dangerous.

Volta Alessandro (1745-1827)
Italian physicist, one of the founders of electric current doctrine, created the first galvanic element.

But care must be observed in working with lower voltages. Depending on the conditions, the voltage even in several dozen volts may be dangerous. The stress is not more than 42 V.

Galvanic elements create low voltage. Therefore, the lighting network uses an electric current from the generators that create a voltage 127 and 220 V, that is, we produce significantly higher energy.

Questions

1. What are accepted for a voltage unit?
2. What voltage is used in the lighting network?
3. What is the voltage on the poles of the dry element and the acid battery?
4. What voltage units except Volta are applied in practice?

Having certain initial knowledge of electricity, it is hard to imagine how electrical appliances work are working, why they work at all, why it is necessary to turn on the TV in a socket so that it will work, and the lantern is enough for a small battery so that it shines in the dark.

And so we will understand everything in order.

Electricity

Electricity - This is a natural phenomenon confirming the existence, interaction and movement of electrical charges. Electricity was first discovered in the VII century BC. Greek philosopher Fales. Fales drew attention to the fact that if a piece of amber to lose their wool, he begins to attract light items. Amber on ancient Greek - electron.

That's how I imagine, Fales sits, terates a piece of amber about his gymathies (this is woolen outerwear from the ancient Greeks), and then with a puzzled look looks like a hair, scraps, feathers and pieces of paper attract.

This phenomenon is called static electricity. You can repeat this experience. To do this, spend the usual plastic line with a woolen cloth and bring it to small paper pieces.

It should be noted that for a long time this phenomenon has not been studied. And only in 1600 in his essay "On Magnifies, magnetic bodies and a large magnet-land", the English naturalist William Gilbert introduced the term - electricity. In his work, he described his experiments with electrified objects, and also found that other substances can be electrified.

Next, for three centuries, the most advanced scientists of the world explore electricity, they write treatises, formulate laws, invent electric cars and only in 1897, Joseph Thomson opens the first material carrier of electricity - electron, a particle, thanks to which electrical processes in substances are possible.

Electron - This is an elementary particle, has a negative charge approximately equal -1,602 · 10 -19 CL (pendant). Denotes e. or e -.

Voltage

To make the charged particles move from one pole to another you need to create between poles potential difference or - Voltage. Voltage measurement unit - Volt (AT or V.). In formulas and calculations, the voltage is indicated by the letter V. . In order to get the voltage of 1 in need to transfer between the poles charge in 1 cl, while performing the work in 1 J (Joule).

For clarity, imagine a reservoir with water located at some height. The tank comes out pipe. Water under natural pressure leaves the tank through the pipe. Let's agree that water is electric charge, waterpover height (pressure) is voltage, and the flow rate of water is electricity.

Thus, the more water in the tank, the higher the pressure. Similarly, from an electrical point of view, the more charge, the higher the voltage.

Let's start dragging the water, the pressure will decrease. Those. The charge level is descended - the voltage value decreases. Such a phenomenon can be observed in the flashlight, the light bulb shines everything in the dark as the batteries are discharged. Pay attention than the less water pressure (voltage), the lower the flow of water (current).

Electricity

Electricity - this is a physical process of directional movement of charged particles under the action of electro magnetic field from one pole closed electrical chain to another. Electrons, protons, ions and holes can act as particles carrying the charge. In the absence of a closed circuit, the current is not possible. Particles capable of transferring electric charges There are not in all substances that they are in which they are called conductors and semiconductors. And substances in which there are no such particles - dielectrics.

Current force measurement unit - Ampere (BUT). In formulas and calculations, the strength of the current is indicated by the letter I. . The current of 1 ampere is formed when passing through the electric charge circuit in 1 pendant (6,241 · 10 18 electrons) in 1 second.

Re-turn to our analogy water - electricity. Only now take two reservoirs and fill them with an equal amount of water. The difference between the tanks in the diameter of the output tube.

We will open the cranes and make sure that the flow of water from the left tank is greater (the diameter of the pipe is greater) than from the right. Such experience is clear evidence of the dependence of the flow rate from the pipe diameter. Now let's try to equalize two streams. To do this, add to the right water tank (charge). This will give greater pressure (voltage) and increase the flow rate (current). In the electrical circuit in the role of the pipe diameter protrudes resistance.

Experiments performed clearly demonstrate the relationship between voltage, tokom and resistance. Let's talk more about the resistance a little later, and now a few more words about the properties of the electric current.

If the voltage does not change its polarity, plus for minus, and the current flows in one direction, then d.C. and correspondingly constant pressure. If the voltage source changes its polarity and current flows in one direction, then in the other - it is already alternating current and aC voltage. Maximum and minimum values \u200b\u200b(on the chart are indicated as IO. ) - this is amplitude or peak current values. In domestic sockets, the voltage changes its polarity 50 times per second, i.e. The current fluctuates that there, then it turns out that the frequency of these oscillations is 50 hertz or abbreviated 50 Hz. In some countries, for example, the frequency of 60 Hz is adopted in the United States.

Resistance

Electrical resistance - The physical value determining the property of the conductor to prevent (resist) the current passage. Resistance Measurement Unit - Oh. (denotes Oh. or the Greek letter of Omega Ω ). In formulas and calculations, the resistance is indicated by the letter R. . Resistance in 1 ohm has a conductor to the poles of which the voltage of 1 V is applied and flows 1 A.

Conductors are conducted differently. Them conductivity Depends, first of all, from the material of the conductor, as well as from the section and length. The greater the cross section, the higher the conductivity, but, the larger length, the conductivity below. Resistance is the inverse concept of conductivity.

Using the example of the plumbing model, the resistance can be represented as the diameter of the pipe. Than it is less, the worse conductivity and above resistance.

The conductor resistance is manifested, for example, in the heating of the conductor when current flows in it. Moreover, the more current and less the conductor cross section - the stronger the heating.

Power

Electric power - This is a physical value that determines the rate of electricity transformation. For example, you have repeatedly heard: "Light bulb on so much watt." This is the power consumed by a light bulb per unit of time during operation, i.e. transformation of one type of energy to another at some speed.

Electricity sources, such as generators, is also characterized by a power, but already generated per unit of time.

Power Measurement Unit - Watt (denotes T. or W.). In formulas and calculations, the power is indicated by the letter P. . For alternating current circuits, the term applies Full power , unit - Volt-ampere (B · A. or V · A.), denoted by the letter S. .

And at the end of Electric chain. This chain is a set of electrical components that can conduct an electric current and interconnected according to itself.

What we see in this image is an elementary electrical appliance (flashlight). Under the action of tension U. (C) source of electricity (batteries) on conductors and other components with different resistances 4.59 (223 votes)

This page briefly outlines the main values \u200b\u200bof electric current. As needed, the page will be replenished with new values \u200b\u200band formulas.

Tok Power - Quantitative measure of the electric current flowing through the cross section of the conductor. The thicker the conductor, the greater the current can flow over it. The strength of the current is measured by the device called an ammeter. Unit of measurement - ampere (A). The strength of the current is denoted by the letter - I..

It should be added that the constant and alternating current of the low frequency flows through the entire section of the conductor. The high-frequency alternating current flows only on the surface of the conductor - the skin layer. The higher the current frequency, the thinner skin-layer Explorer through which high-frequency current flows. This applies to any high-frequency elements - conductors, inductors, waveguides. Therefore, to reduce the active resistance of the conductor with high-frequency current, the conductor with a large diameter is selected, and its silver (as is known, silver has a very small resistivity).

Voltage (voltage drop) - Quantitative measure of the potential difference (electrical energy) between the two points of the electrical circuit. The voltage of the current source is the difference of potentials at the output of the current source. Voltage voltage is measured. Unit of measurement - Volt (B). The voltage is indicated by the letter - U., power supply voltage (synonym - electromotive force) can be denoted by the letter - E..

where U. - voltage drop on the electrical chain element, I. - Current flowing through the chain element.

Scattered (absorbed) power element electrical circuit - The power value dispersed on the chain element that the element can absorb (to withstand) without changing its nominal parameters (failure). The dispersion capacity of the resistors is denoted in its name (for example: two watt resistor - OMLT-2, ten watt wire resistor - PEV-10). When calculating schemesThe value of the necessary dispersed power of the chain element is calculated by the formulas:

For reliable operation defined by the formulas, the value of the dissipated power of the element is multiplied by the coefficient of 1.5, taking into account the fact that the power supply should be provided.

The conductivity of the chain element - The ability of the chain element to carry out an electric current. Single measurement unit - Siemens (cm). Denotes the conductivity of the letter - σ . Conductivity - the amount of reverse resistance, and is associated with it formula:

If the conductor resistance is 0.25 ohms (or 1/4 ohms), then the conductivity will be 4 Siemens.

Electric current frequency - Quantitative measure characterizing the rate of changes in the direction of electric current. There are concepts - circular (or cyclic) frequency - Ωdetermining the rate of change of the phase of the electric (magnetic) field and electric current frequency - fwhich characterizes the rate of changes in the direction of electric current (once or oscillations) in one second. The frequency is measured by an instrument called frequency meter. Unit of measurement - Hertz (Hz). Both frequencies are connected with each other through the expression:

Electric current period - The value of the reverse frequency showing for which time the electric current performs one cyclic oscillation. The period is measured, as a rule, using an oscilloscope. Unit of measurement of the period - second (C). The period of oscillation of electric current is indicated by the letter - T.. The period is associated with an electric current frequency by expression:

The wavelength of the high-frequency electromagnetic field - Dimensional value characterizing one period of oscillation of the electromagnetic field in space. The wavelength is measured in meters (m). The wavelength is indicated by the letter - λ . The wavelength is associated with frequency and is determined through the speed of light propagation:

Reactive resistance of inductance coil (choke) - The value of the internal resistance of the inductance coil of the variable harmonic current at its defined frequency. Reactive resistance of the inductance coil is indicated X L. and determined by the formula:

Resonant frequency of the oscillating circuit - the frequency of harmonic alternating current on which the oscillating circuit has a pronounced amplitude-frequency characteristic (ACH). The resonant frequency of the oscillating circuit is determined by the formula.

Electricity is perceived by us as a given and hardly who is thinking about what electrical voltage is and what is its physical entity when includes light, computer or washing machine. In fact, it deserves much more attention, and not only because it may be fatally dangerous, but also due to the fact that humanity, mastering this kind of energy, made a high-quality civilization leap.

Recall one of the most interesting moments at the school lesson of physics, when the teacher rotated the disk of the electric car, and there was a spark between metal balls. This is the visible reflection of the natural phenomenon called the electric current. It arises due to the fact that on one ball of negatively charged ions more, and there is less on the other, because of what the potential difference arises, that is, a fact that violates the basic law of nature - energy conservation.

Negatively charged particles seek to move to where they are less, thereby resetting the difference. Of course, the electrons do not pass the whole path between charged balls called poles. Their mileage limits the crystal lattice, the nodes of which they cannot leave. But you can hit the adjacent particles and transfer the pulse along the chain further, creating the effect of dominoes. Each such impact generates a splash of energy, which is why the system moves from the state of rest in an excited, which is customized with electrical voltage.

Strength, driving charged particles

To put on the service of electrical stress and current, a person had to find power, which could resume the difference between the potentials between the poles, generating the continuous collision of the crystal lattice particles. They turned out as many as three:

1. Electromagnetic induction - the occurrence of current as a result of interdependent movement of metals in a magnetic field. Used in direct and alternating current generators.
2. Electrochemical interaction generated by the difference in potentials of crystalline lattices of substances. Used in batteries, DC power batteries.
3. The thermochemical reaction that increases the activity of electrons as a result of heating.

The force generating the movement of charged particles received the name "Elektring" (EMF Abbreviation) and is indicated in the schemes of the letter "E", usually related to the mimony of the connectors to which the power supply is connected.

Volta and amperes

EMF and stress are measured in a volt - a conditional unit called in honor of the Italian Alessandro Volta, the officially recognized inventor of a galvanic battery is a source of direct current. This is the amount of work that is performed when the charge unit is moved (Cool), if 1 joele of conditional energy was spent.

However, there is a second unit of measurement of electric current - ampere, named after French physics Andre-Marie Ampere. Traditionally, it is called the power of current, although it is more correct to apply the term "magnetotor-livestorm force", which most fully reflects the dual physical essence of the charged particle.

Magnetic I. electric field Electron tend to mutual compensation, and their dependence is determined by the law of OMA described by the formula I \u003d U / R. If the resistance of the medium drops sharply (for example, with a short circuit), the current increases by exponential. This causes a response voltage drop, as a result of which the system comes into an equilibrium state. A similar effect can be noticed during the operation of the welding transformer, when the incandescent lamp arc occurs almost overtaken.

There is another effect: with a large impedance of the medium, the charge of one sign is copied onto any surface until the voltage reaches the critical level, after which the test (current occurrence) occurs in the direction of the surface with the highest potential difference. Static voltage is extremely dangerous, because at the time of discharge it can generate currents by force in hundreds of amps. Therefore, metal structures, for a long time in a magnetic field, are necessarily ground.

Permanent or variable?

Voltage is a static component of electricity, and the current is dynamic, because its direction changes together with polarity at the ends of the conductor. And this property turned out to be very useful for the spread of electricity in the world. The fact is that any current fades due to the internal resistance of the medium, according to the same energy conservation law. But it turned out that moving in one direction the flow of electrons is very difficult to increase, and the cyclically changing direction is simple, for this, a transformer with two windings on one core is used.

To obtain an alternating current, it is necessary to turn inside out the principle, open by the Faraday, which in its prototype of the electric generator rotated the copper disk in the permanent magnet action field. Nikola Tesla did on the contrary - placed the rotating electromagnet inside the fixed winding, having received an unexpected effect: at the time of passing the poles through the neutral of the magnetic field, the voltage amplitude drops to zero, and then grows again, but already with another sign. In one turn, the direction of movement of electrons in the conductor changes twice, constituting the working phase. Therefore, alternating current is also called phase. And the voltage generating it is sinusoidal.

Nikola Tesla created a generator with two windings, located at an angle of 90 0 to each other, and the Russian engineer M.O. Dolo-Dobrovolsky has improved him, placing three in the stator, which increased the stability of the electrical machine. As a result, industrial alternating current has become three-phase.

Why 220 volts 50 Hz?

In our country household single-phase network It has a rating of 220 volts and 50 hertz. The reason for the appearance of these numbers is very interesting.

Palm Championship in the domestic development of electricity belongs to Thomas Edison. It used an exceptionally constant current, since the brilliant invention of the Nikola of the Variable Tesla has not happened.

The first electrical device was the incandescent lamp with coal thread. The experimental way was found that it is best working at a 45 volt voltage and a ballast resistance circuit, which ensures the scattering of another twenty. The acceptable duration of the work was provided by the sequential inclusion of two lamps. Total in the household network, according to Edison, it was supposed to be 110 volts.

However, the transfer of direct current from the power plants to consumers was accompanied by great difficulties: after one or two miles, he faded completely. According to the law of Joule - Lenz, the amount of heat dissipated by the conductor during current passage is calculated according to the following formula: Q \u003d R. I 2. To reduce the losses fourly, the voltage increased to 220 volts, and the power line was built of three conductors - with two "pluses" and one "minus". The consumer received all the same 110 volts.

The confrontation of Nikola Tesla and Thomas Edison, named "War of currents", decided in favor of a variable, since it could be transmitted over long distances with minimal losses. Nevertheless, the voltage between the power conductors remained 220, and the linear, incoming to the consumer - 127 volts, since due to the phase shift by 120 degrees, the voltage amplitude is not arithmetic, and multiply by 1.73 - the root square of three is multiplied.

In the USSR, a networking face value of 127 volts in one phase was used before the early 60s. In the course of improving the electrical lines conducted to increase the transmitted power, the designers went along the same way as Edison - raised tension.

The reference point was taken by 220 volts, which were measured between the phases. It has become a domestic. And the industrial interfacial voltage of 380 volts turned out to multiply 220 per 1.73. The frequency of 50 Hz is 3 thousand oscillations per minute, that is, the optimal number of rotation of the diesel crankshaft or other internal combustion engine, which activates the AC machine.

Now you know what the voltage and electric current is in which they are measured and how they depend on each other, and also why there are 220 volts in your outlet. The above facts do not wear academic nature and do not claim the truth in the last instance. You can familiarize yourself with the nature of this phenomenon in more detail in the textbooks on electrical engineering.