What a value is called electrical voltage. Measurement of voltage, current, spores, containers, inductance, power in electrical circuits. How voltage occurs

Electric current (I) is called the directional movement of electrical charges (ions - in electrolytes, conduction electrons in metals).
A prerequisite for electric current is a closure of an electrical circuit.

Electric current is measured in amperes (a).

Derived units of current measurement are:
1 kiloamper (ka) \u003d 1000 A;
1 milliamper (MA) 0.001 A;
1 Micronomer (MCA) \u003d 0.000001 A.

A person begins to feel the current passing through his body at 0.005 A. current more than 0.05 and dangerous for human life.

Electrical voltage (U) The potential difference between the two points of the electric field is called.

Unit the difference of electrical potentials Is Volt (B).
1 B \u003d (1 W): (1 A).

Derivatives of voltage measurement units are:

1 kilovolt (kV) \u003d 1000 V;
1 Millivolt (MV) \u003d 0.001 V;
1 Microvolt (MKV) \u003d 0.00000 1 V.

Resistance of the plot of electrical circuit It is called the value depending on the material of the conductor, its length and cross-section.

Electrical resistance is measured in Omah (OM).
1 Ohm \u003d (1 B): (1 A).

Derived units of measurement of resistance are:

1 kilome (com) \u003d 1000 ohms;
1 mega (IOM) \u003d 1 000 000 Ohm;
1 billion (MOM) \u003d 0.001 Ohms;
1 micro (MCOM) \u003d 0.00000 1 Ohm.

The electrical resistance of the human body, depending on a number of conditions, ranges from 2000 to 10,000 Ohm.

Specific electrical resistance (ρ) It is called wire resistance with a length of 1 m and a cross section of 1 mm2 at a temperature of 20 ° C.

The value inverse resistivity is called a specific electrical conductivity (Γ).

Power (P) Called the value characterizing the rate with which the energy conversion occurs, or the speed that work is performed.
The generator capacity is the value characterizing the speed with which mechanical or other energy is converted to the generator to the electric.
The power of the consumer is called the value characterizing the speed with which the electrical energy conversion occurs in separate areas of the chain into other useful types of energy.

The system unit of power in C is watt (W). It is equal to the power at which a 1 second is working in 1 JOUL:

1W \u003d 1J / 1SEK

Derived units of electrical power measurement are:

1 kilowatt (kW) \u003d 1000 W;
1 megawatt (MW) \u003d 1000 kW \u003d 1 000 000 W;
1 Millivatt (MW) \u003d 0.001 W; o1i.
1 horsepower (l. P.) \u003d 736 W \u003d 0.736 kW.

Electrical energy measurement units are:

1 watt-second (W s) \u003d 1 j \u003d (1 H) (1 m);
1 kilowatt-hour (kWh) \u003d 3, b 106 W sec.

Example. The current consumed by the electric motor connected to the 220 V network was 10 A for 15 minutes. Determine the energy consumed by the engine.
W * second, or, dividing this amount per 1000 and 3600, we get energy in kilowatt clock:

W \u003d 1980000 / (1000 * 3600) \u003d 0.55kW * h

Table 1. Electric values \u200b\u200band units

Surely, each of us, at least once in life, arose questions about what the current is voltage current, charge, etc. All of this constituting one large physical concept - electricity. Let's, on the simplest examples, try to explore the basic patterns of electrical phenomena.

What is electricity.

Electricity is a combination of physical phenomena associated with the occurrence, accumulation, interaction and transfer of an electric charge. According to most historians of science, the first electrical phenomena were opened by an ancient Greek philosopher Fales in the seventh century BC. Fales observed the action of static electricity: attraction to rubbed wool amber light items and particles. To repeat this experience yourself you need to lose about woolen or cotton fabric. Any plastic object (for example, a handle or a ruler) and bring it to fine pieces of paper.

The first serious scientific work, which describes the study of electrical phenomena, became the treatise of the English scientist William Gilbert "On Magnet, magnetic bodies and a large magnet-land" published in 1600. In this paper, the author described the results of his experiments with magnets and electrified bodies. Here the term electricity is mentioned for the first time.

Research W. Gilbert gave a serious impetus to the development of science on electricity and magnetism: for the period from early 17 to the end of the 19th century a large number of experiments were carried out and the main laws describing electromagnetic phenomena were formulated. And in 1897, the English physicist Joseph Thomson opened an electron - an elementary charged particle, which determines the electrical and magnetic properties of the substance. The electron (in ancient Greek, the electron is an amber) has a negative charge approximately equal to 1.602 * 10-19 CL (Cool) and a mass of 9.109 * 10-31 kg. Thanks to electrons and other charged particles, electrical and magnetic processes occur in substances.

What is voltage.

There are constant and variable electric currents. If the charged particles are constantly moving in one direction, then in the chain - permanent current and, accordingly, dC voltage. If the direction of movement of the particles periodically changes (they move in one, then in the other direction), then this is an alternating current and it occurs, respectively, if there is an alternating voltage (i.e., when the potential difference changes its polarity). For AC, it is characterized by a periodic change in the value of the current strength: it takes the maximum, then the minimum value. These current strength values \u200b\u200bare amplitude, or peak. The frequency of changes in the polarity of the voltage can be different. For example, in our country, this frequency is 50 hertz (i.e., the voltage changes its polarity 50 times per second), and in the US frequency of alternating current - 60 Hz (hertz).

The lesson is devoted to considering the concept of electrical stress, its designation and units of measurement. The second part of the lesson is assigned mainly to demonstrate the voltage measurement devices on the chain area and their features.

If we bring a standard example of the meaning of all known inscriptions on any homemade household devices "220 V", it means that 220 J to move the charge of 1 CL on the chain area.

Formula for voltage calculation:

The work of the electric field to transfer charge, J;

Charge, cl.

Therefore, the voltage measurement unit can be represented as follows:

Between the formulas for calculating the voltage and current strength, there is a relationship to which attention should be paid: and. In both formulas there is an electrical charge, which may be useful when solving some tasks.

To measure the voltage use the device called voltmeter (Fig. 2).

Fig. 2. Voltmeter ()

There are various voltmeters according to the features of their application, but the principle of their work is the electromagnetic effect of the current. All voltmeters of the Latin letter, which is applied to the dial of the instruments and is used in the schematic image of the device.

In school conditions, such as voltmeters shown in Figure 3. With their help, voltage measurements in electrical circuits are carried out during laboratory work.

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Fig. 3. Voltmeters

The main elements of the demonstration voltmeter are the case, scale, arrow and terminals. Terminals are usually signed with a plus or minus and for clarity are highlighted with different colors: red - plus, black (blue) - minus. This is done to know the device terminals to contact the appropriate wire connected to the source. In contrast to the ammeter, which is included in the rupture of the chain successively, the voltmeter is turned on in the chain in parallel.

Of course, any electrical measuring device must minimally influence the chain under study, so the voltmeter has such structural features that it is minimal current through it. Such an effect is ensured by the selection of special materials, which contribute to the minimal flow rate through the device.

Schematic image of a voltmeter (Fig. 4):

Fig. four.

Pictures for example an electrical circuit (Fig. 5), in which a voltmeter is connected.

Fig. five.

In the chain, almost the minimum set of elements: the current source, the incandescent lamp, the key, the ammeter connected sequentially, and the voltmeter connected in parallel to the light bulb.

Comment. It is better to start the assembly of the electrical circuit from all elements, except for the voltmeter, and it is already connected at the end.

There are many different types of voltmeters with differing scales. Therefore, the question of calculating the price of the device in this case is very relevant. Mikersoltmeters, millivollatmeters, simply voltmeters, etc. are very common, simply voltmeters, etc. According to their names, it is understood with what multiple measurements are made.

In addition, voltmeters are divided into DC and AC devices. Although in the urban network and alternating current, but at this stage of studying physics we are engaged in a constant current, which serves all galvanic elements, so we will be interested in the corresponding voltmeters. The fact that the device is intended for the AC circuits is made on the clock in the form of a wavy line (Fig. 6).

Fig. 6. AC Voltmeter ()

Comment. If we talk about voltage values, then, for example, the voltage 1 V is a small value. The industry uses much greater voltages, measured by hundreds of volts, kilovolts and even megavolites. In everyday life, voltage 220 V and less are used.

In the next lesson, we learn what electrical resistance of the conductor.

Bibliography

1. Gentenestein L. E, Kaidalov A. B., Kozhevnikov V. B. Physics 8 / Ed. Orlova V. A., Roizen I. I. - M.: Mnemozin.
2. Pryrickin A. V. Physics 8. - M.: Drop, 2010.
3. Fadeeva A. A., Zasov A. V., Kiselev D. F. Physics 8. - M.: Enlightenment.

Additional R.recommended Links to Internet Resources

1. Cool physics ().
2. YouTube ().
3. YouTube ().

Homework

The load in the electrical circuit is characterized by the current power, the current measurement in amperes. The current strength sometimes has to be measured to test the permissible magnitude of the load on the cable. For laying the electrical line, cables of different sections are used. If the cable works with a load above the permissible value, then it is heated, and the insulation is gradually collapsed. As a result, this leads to and replacing the cable.

• After laying a new cable, you need to measure the current passing through it with all running electrical devices.
• If an additional load is connected to the old wiring, then you should also check the current value that should not exceed the permissible limits.
• With the load equal to the upper permissible limit, the current correspondence occurs through. Its value should not exceed the nominal value of the operating current of the machine guns. Otherwise, the circuit breaker will de-energize the network due to overload.
• The current measurement is also necessary to determine the operation modes of electrical devices. Measuring the current load of electric motors is performed not only to check their performance, but also to detect the load above the permissible, which may occur due to the large mechanical effort when the device is working.
• If you measure the current in the chain of the working, then it will show the serviceability.
• The performance in the apartment is also checked by the current measurement.

Current power

In addition to the current, there is the concept of current power. This parameter determines the current operation per unit time. The power of the current is equal to the ratio of the work performed by the time interval for which this work was performed. Denote by the letter "P" and measured in watts.

Power is calculated by multiplying the voltage of the network for the current consumed by the connected electrical devices: P \u003d U X I. Typically, the electrical devices indicate the power consumed by which the current can be defined. If your TV has a power of 140 W, then to determine the current divide this value by 220 V, as a result we get 0.64 amps. This is the value of the maximum current, in practice the current may be less when a decrease in the brightness of the screen or other changes in settings.

Measuring current to devices

To determine the consumption of electrical energy, taking into account the operation of consumers in different modes, electrical measuring instruments are needed, capable of measuring the current parameters.

• . To measure the values \u200b\u200bof the current in the chain, special devices are used, called ammeters. They are included in the measured chain on a serial scheme. The internal resistance of the ammeter is very small, so it does not affect the parameters of the chain. The ammeter can be marked in amperes or other shares of the amperes: microampers, milliamperes, etc. There are several types of ammeters: electronic, mechanical, etc.

• It is an electronic measuring device capable of measuring different parameters of the electrical circuit (resistance, voltage, conductor break, battery suitable, etc.), including current strength. There are two types of multimeters: digital and analog. In the multimeter there are various measurement settings.

The procedure for measuring current force by a multimeter:

• Find out what the measurement interval of your multimeter. Each device is designed to measure the current in some interval, which must correspond to the measured electrical circuit. The greatest allowable measurement current must be specified in the instructions.
• Select the appropriate measurement mode. Many multimeters are capable of working in different modes, and measure different values. For measurements, current strength must be switched to the appropriate mode, considering the current (permanent or variable).
• Install the necessary measurement interval on the device. It is better to establish the upper limit of the current strength somewhat above the alleged value. You can reduce this limit at any time. But it will be a guarantee that you will not bring the device in order.
• Insert the measuring plugs of wires into the socket. The device includes two wires with affairs and connectors. Nests must be marked on the instrument or depicted in the passport.

• To start the measurement, you must connect the multimeter to the chain. This should follow the safety rules and do not touch the current parts of the unprotected parts of the body. It is impossible to measure in a humid environment, since the moisture conducts an electric current. On the hands you should wear rubber gloves. To break the chain for measuring, you should cut the conductor and deteriorate insulation at both ends. Then connect the multimeter probe to the stripped ends of the wire and make sure in good contact.
• Turn on the circuit power and fix the instrument readings. If necessary, adjust the upper measurement limit.
• Disable the power circuit and disconnect the multimeter.
• . If you need to measure the current without breaking the electrical circuit, the measuring ticks will be an excellent option for performing this task. This device produces several species, and different designs. Some models can measure other parameters of the chain. Use the measuring current ticks is very convenient.

Ways to measure current

To measure the current force in the electrical circuit, one ampermeter is necessary or another instrument that can measure the current strength, connect to the positive terminal of the current source or, and the other output to the consumer's wire. After that, the current strength can be measured.

When measuring, it is necessary to observe accuracy, since an electric arc may occur when the operating electrical circuit is broken.

To measure the power of the electrical devices connected directly to the outlet or the household network cable, the measuring device is configured to an AC mode with an overpriced upper boundary. Then the measuring instrument is connected to the gap of the phase wire.

All connections and disconnection work is allowed only in a de-energized chain. After all connections, you can feed meals and measure the current strength. At the same time it is impossible to concern the bare-cutting parts, in order to avoid electric shock. Such measurement methods are inconvenient and create a certain danger.

It is much more convenient to measure the measurements by current-measuring tongs that can perform all the functions of the multimeter, depending on the execution of the device. It is very simple to work with such ticks. You need to configure the measurement mode of a direct or alternating current, dilute the mustache and cover the phase wire. Then you need to check the density of the ordinance of the mustache between themselves and measure the current. For correct readings, it is necessary to cover only the phase wire. If you cover two wires at once, then measurements will not work.

Current testers serve only for measurement of alternating current parameters. If they are used to measure direct current, then the mustache will be freezed with a lot of force, and it will be possible to push them only by turning off the power.

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 are attracted by Yantary.

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 (IN 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 an electromagnetic field from one pole of a closed electrical circuit 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 carrying electrical charges exist 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 having different resistances 4.59 (237 votes)