Match the units of measurement and their designation. How is voltage measured

Consider a physical record m=4kg. In this formula "m"- designation of physical quantity (mass), "4" - numerical value or magnitude, "kg"- unit of measurement of a given physical quantity.

The values ​​are of different kinds. Here are two examples:
1) The distance between points, the lengths of segments, broken lines - these are quantities of the same kind. They are expressed in centimeters, meters, kilometers, etc.
2) The durations of time intervals are also quantities of the same kind. They are expressed in seconds, minutes, hours, etc.

Quantities of the same kind can be compared and added:

BUT! It is pointless to ask which is greater: 1 meter or 1 hour, and you cannot add 1 meter to 30 seconds. The duration of time intervals and distance are quantities of various kinds. They cannot be compared or combined.

Values ​​can be multiplied by positive numbers and zero.

Taking any value e per unit of measurement, it can be used to measure any other quantity a the same kind. As a result of the measurement, we get that a=x e, where x is a number. This number x is called the numerical value of the quantity a with unit of measurement e.

There are dimensionless physical quantities. They do not have units of measurement, that is, they are not measured in anything. For example, the coefficient of friction.

What is SI?

According to Professor Peter Kampson and Dr. Naoko Sano of Newcastle University, published in the journal Metrology (Metrology), the kilogram standard adds an average of about 50 micrograms per hundred years, which in the end can significantly affect very many physical quantities.

The kilogram is the only SI unit that is still defined using a standard. All other measures (meter, second, degree, ampere, etc.) can be determined with the required accuracy in a physical laboratory. The kilogram is included in the definition of other quantities, for example, the unit of force is the newton, which is defined as the force that changes the speed of a 1 kg body by 1 m/s in the direction of the force in 1 second. Other physical quantities depend on the Newton value, so that in the end the chain can lead to a change in the value of many physical units.

The most important kilogram is a cylinder with a diameter and height of 39 mm, consisting of an alloy of platinum and iridium (90% platinum and 10% iridium). It was cast in 1889 and is stored in a safe at the International Bureau of Weights and Measures in the city of Sèvres near Paris. The kilogram was originally defined as the mass of one cubic decimeter (liter) of pure water at 4°C and standard atmospheric pressure at sea level.

Initially, 40 exact copies were made from the kilogram standard, which were sold all over the world. Two of them are located in Russia, at the All-Russian Research Institute of Metrology. Mendeleev. Later, another series of replicas was cast. Platinum was chosen as the base material for the reference because of its high oxidation resistance, high density, and low magnetic susceptibility. The standard and its replicas are used to standardize the mass in a wide variety of industries. Including where micrograms are essential.

Physicists believe that weight fluctuations are the result of atmospheric pollution and changes chemical composition on the surface of the cylinders. Despite the fact that the standard and its replicas are stored in special conditions, this does not save the metal from interacting with environment. Accurate weight kilograms was determined using X-ray photoelectron spectroscopy. It turned out that the kilogram “recovered” by almost 100 mcg.

At the same time, copies of the standard from the very beginning differed from the original and their weight also changes in different ways. So, the main American kilogram initially weighed 39 micrograms less than the standard, and a check in 1948 showed that it had increased by 20 micrograms. Another American copy, on the contrary, is losing weight. In 1889, the kilogram number 4 (K4) weighed 75 micrograms less than the standard, and in 1989 already 106.

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 the electric field (in J) does to transfer the charge, and “q” is the charge itself, in coulombs.

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. Different types of 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.

Content:

Electric current is characterized by such quantities as current strength, voltage and resistance, interconnected. Before considering the question of what voltage is measured in, it is necessary to find out exactly what this value is and what its role in the formation of current is.

How voltage works

The general concept of electric current is the directed movement of charged particles. These particles are electrons, the movement of which occurs under the influence of an electric field. The more charges you need to move, the more work is done by the field. This work is affected not only by the current strength, but also by the voltage.

The physical meaning of this value is that the work of the current in any section of the circuit is correlated with the amount of charge that passes through this section. In the process of this work, a positive charge moves from a point where there is a small potential to a point with great value potential. Thus, voltage is defined as or electromotive force, and work itself is energy.

The work of an electric current is measured in joules (J), and the amount of electric charge is a pendant (C). As a result, the voltage is a ratio of 1 J/C. The resulting unit of voltage is called the volt.

To clearly explain the physical meaning of stress, you need to refer to the example of a hose filled with water. In this case, the volume of water will play the role of current, and its pressure will be equivalent to voltage. When water moves without a tip, it moves freely and in large quantities through the hose, creating low pressure. If you press the end of the hose with your finger, then there will be a decrease in volume while increasing water pressure. The jet itself will travel a much greater distance.

The same thing happens in electricity. The strength of the current is determined by the number or volume of electrons moving through the conductor. The voltage value, in fact, is the force with which these electrons are pushed. It follows that, under the condition of the same voltage, the conductor conducting large quantity current, must also have a large diameter.

Voltage unit

The voltage can be constant or variable, depending on the current. This value can be denoted as the letter B (Russian designation) or V, corresponding to the international designation. To indicate alternating voltage, the symbol "~" is used, which is placed in front of the letter. For constant voltage, there is a “-” sign, but in practice it is almost never used.

When considering the question of what voltage is measured in, it should be remembered that for this there are not only volts. Larger values ​​are measured in kilovolts (kV) and megavolts (mV), which means 1 thousand and 1 million volts, respectively.

How to measure voltage and current

INTRODUCTION

A physical quantity is a characteristic of one of the properties of a physical object (physical system, phenomenon or process), which is qualitatively common to many physical objects, but quantitatively individual for each object.

Individuality is understood in the sense that the value of a quantity or the size of a quantity can be for one object a certain number of times greater or less than for another.

The value of a physical quantity is an estimate of its size in the form of a certain number of units accepted for it or a number according to the scale adopted for it. For example, 120 mm is the value of a linear value; 75 kg is the value of body weight.

There are true and real values ​​of a physical quantity. A true value is a value that ideally reflects a property of an object. Real value - the value of a physical quantity, found experimentally, close enough to the true value that can be used instead.

The measurement of a physical quantity is a set of operations for the use of a technical means that stores a unit or reproduces a scale of a physical quantity, which consists in comparing (explicitly or implicitly) the measured quantity with its unit or scale in order to obtain the value of this quantity in the form most convenient for use.

There are three types of physical quantities, the measurement of which is carried out according to fundamentally different rules.

The first type of physical quantities includes quantities on the set of dimensions of which only the order and equivalence relations are defined. These are relationships like "softer", "harder", "warmer", "colder", etc.

Quantities of this kind include, for example, hardness, defined as the ability of a body to resist the penetration of another body into it; temperature, as the degree of body heat, etc.

The existence of such relationships is established theoretically or experimentally with the help of special means of comparison, as well as on the basis of observations of the results of the impact of a physical quantity on any objects.

For the second type of physical quantities, the relation of order and equivalence takes place both between sizes and between differences in pairs of their sizes.

A typical example is the scale of time intervals. So, the differences of time intervals are considered equal if the distances between the corresponding marks are equal.

The third type is additive physical quantities.

additive physical quantities quantities are called, on the set of sizes of which not only the relations of order and equivalence are defined, but also the operations of addition and subtraction

Such quantities include, for example, length, mass, current strength, etc. They can be measured in parts, and also reproduced using a multi-valued measure based on the summation of individual measures.

The sum of the masses of two bodies is the mass of such a body, which is balanced on the first two equal-arm scales.

The dimensions of any two homogeneous PV or any two sizes of the same PV can be compared with each other, i.e., find how many times one is larger (or smaller) than the other. To compare m sizes Q", Q", ... , Q (m) with each other, it is necessary to consider C m 2 of their relationship. It is easier to compare each of them with one size [Q] of a homogeneous PV, if we take it as a unit of the PV size, (abbreviated as a PV unit). As a result of such a comparison, we obtain expressions for the dimensions Q", Q", ... , Q (m) in the form of some numbers n", n", .. . ,n (m) PV units: Q" = n" [Q]; Q" = n"[Q]; ...; Q(m) = n(m)[Q]. If the comparison is carried out experimentally, then only m experiments are required (instead of C m 2), and the comparison of the sizes Q", Q", ... , Q (m) with each other can be performed only by calculations like

where n (i) / n (j) are abstract numbers.

Type equality

is called the basic measurement equation, where n [Q] is the value of the size of the PV (abbreviated as the value of the PV). The PV value is a named number, composed of the numerical value of the PV size, (abbreviated as the numerical value of the PV) and the name of the PV unit. For example, with n = 3.8 and [Q] = 1 gram, the size of the mass Q = n [Q] = 3.8 grams, with n = 0.7 and [Q] = 1 ampere, the size of the current strength Q = n [Q ] = 0.7 amperes. Usually, instead of “the size of the mass is 3.8 grams”, “the size of the current is 0.7 amperes”, etc., they say and write more briefly: “the mass is 3.8 grams”, “the current is 0.7 amperes " etc.

The dimensions of the PV are most often found as a result of their measurement. The measurement of the size of the PV (abbreviated as the measurement of the PV) consists in the fact that by experience, using special technical means, the value of the PV is found and the proximity of this value to the value that ideally reflects the size of this PV is estimated. The PV value found in this way will be called nominal.

The same Q dimension can be expressed different values with different numerical values ​​depending on the choice of the PV unit (Q = 2 hours = 120 minutes = 7200 seconds = = 1/12 days). If we take two different units and , then we can write Q = n 1 and Q = n 2, whence

n 1 / n 2 \u003d /,

i.e., the numerical values ​​of the PV are inversely proportional to its units.

From the fact that the size of the PV does not depend on its chosen unit, the condition for the unambiguity of measurements follows, which consists in the fact that the ratio of two values ​​of a certain PV should not depend on which units were used in the measurement. For example, the ratio of the speeds of a car and a train does not depend on whether these speeds are expressed in kilometers per hour or meters per second. This condition, which at first glance seems indisputable, unfortunately, cannot yet be met when measuring some PVs (hardness, photosensitivity, etc.).

1. THEORETICAL PART

1.1 The concept of a physical quantity

Weight objects of the surrounding world are characterized by their properties. Property is a philosophical category that expresses such a side of an object (phenomenon, process) that determines its difference or commonality with other objects (phenomena, processes) and is found in its relationship to them. The property is a quality category. For a quantitative description of various properties of processes and physical bodies, the concept of quantity is introduced. A value is a property of something that can be distinguished from other properties and evaluated in one way or another, including quantitatively. The value does not exist by itself, it takes place only insofar as there is an object with properties expressed by this value.

An analysis of the values ​​allows us to divide (Fig. 1) them into two types: the values ​​of the material form (real) and the values ​​of ideal models of reality (ideal), which are mainly related to mathematics and are a generalization (model) of specific real concepts.

Real quantities, in turn, are divided into physical and non-physical. A physical quantity in the most general case can be defined as a quantity inherent in material objects (processes, phenomena) studied in the natural (physics, chemistry) and technical sciences. Non-physical quantities should include quantities inherent in the social (non-physical) sciences - philosophy, sociology, economics, etc.

Rice. 1. Classification of quantities.

The document RMG 29-99 interprets a physical quantity as one of the properties of a physical object, which is qualitatively common for many physical objects, but quantitatively individual for each of them. Individuality in quantitative terms is understood in the sense that a property can be for one object a certain number of times more or less than for another.

It is expedient to divide physical quantities into measurable and estimated ones. Measured FIs can be expressed quantitatively as a certain number of established units of measurement. The possibility of introducing and using such units is an important distinguishing feature of the measured PV. Physical quantities for which, for one reason or another, a unit of measurement cannot be introduced, can only be estimated. Evaluation is understood as the operation of assigning a certain number to a given value, carried out according to established rules. Evaluation of the value is carried out using scales. A magnitude scale is an ordered set of magnitude values ​​that serves as the initial basis for measuring a given magnitude.

Non-physical quantities, for which a unit of measurement cannot in principle be introduced, can only be estimated. It should be noted that the estimation of non-physical quantities is not included in the tasks of theoretical metrology.

For a more detailed study of PV, it is necessary to classify, to identify the general metrological features of their individual groups. Possible classifications of FI are shown in fig. 2.

According to the types of phenomena, PVs are divided into:

Real, i.e. quantities describing the physical and physico-chemical properties of substances, materials and products from them. This group includes mass, density, electrical resistance, capacitance, inductance, etc. Sometimes these PVs are called passive. To measure them, it is necessary to use an auxiliary energy source, with the help of which a signal of measuring information is formed. In this case, passive PV are converted into active ones, which are measured;

Energy, i.e. quantities describing the energy characteristics of the processes of transformation, transmission and use of energy. These include current, voltage, power, energy. These quantities are called active.

They can be converted into measurement information signals without the use of auxiliary energy sources;

Characterizing the course of processes in time, This group includes different kind spectral characteristics, correlation functions and other parameters.

In 1875, the International Bureau of Weights and Measures was founded by the Metric Conference; its goal was to create a unified measurement system that would be used throughout the world. It was decided to take as a basis the metric system, which appeared during the French Revolution and was based on the meter and kilogram. Later, the standards of the meter and kilogram were approved. Over time, the system of units of measurement has evolved, now it has seven basic units of measurement. In 1960, this system of units received the modern name International System of Units (SI system) (Systeme Internatinal d "Unites (SI)). The SI system is not static, it develops in accordance with the requirements that are currently placed on measurements in science and technology.

Basic units of measurement of the International System of Units

The definition of all auxiliary units in the SI system is based on seven basic units of measurement. The main physical quantities in the International System of Units (SI) are: length ($l$); mass ($m$); time($t$); electric current strength ($I$); Kelvin temperature (thermodynamic temperature) ($T$); amount of substance ($\nu $); light intensity ($I_v$).

The basic units in the SI system are the units of the above quantities:

\[\left=m;;\ \left=kg;;\ \left=c;\ \left=A;;\ \left=K;;\ \ \left[\nu \right]=mol;;\ \left=cd\ (candela).\]

Standards of the main units of measurement in SI

Here are the definitions of the standards of the main units of measurement as it is done in the SI system.

By meter (m) is called the length of the path that light travels in vacuum in a time equal to $\frac(1)(299792458)$ s.

Mass standard for SI is a weight in the form of a straight cylinder, the height and diameter of which is 39 mm, consisting of an alloy of platinum and iridium weighing 1 kg.

One second (s) called the time interval, which is equal to 9192631779 periods of radiation, which corresponds to the transition between two hyperfine levels of the ground state of the cesium atom (133).

One ampere (A)- this is the strength of the current passing in two straight, infinitely thin and long conductors located at a distance of 1 meter, located in a vacuum generating Ampère force (the force of interaction of conductors) equal to $2\cdot (10)^(-7)H$ for each meter of the conductor .

One kelvin (K) is the thermodynamic temperature equal to $\frac(1)(273,16)$ of the triple point temperature of water.

One mol (mol)- this is the amount of a substance in which there are as many atoms as there are in 0.012 kg of carbon (12).

One candela (cd) is equal to the intensity of light emitted by a monochromatic source with a frequency of $540\cdot (10)^(12)$Hz with an energy force in the direction of radiation $\frac(1)(683)\frac(W)(sr).$

Science is developing, measuring equipment is being improved, the definitions of units of measurement are being revised. The higher the accuracy of measurements, the greater the requirements for the definition of units of measure.

SI derivative quantities

All other quantities are considered in the SI system as derivatives of the main ones. The units of measurement of derived quantities are defined as the result of the product (taking into account the degree) of the main ones. Let us give examples of derived quantities and their units in the SI system.

There are also dimensionless quantities in the SI system, for example, the reflection coefficient or the relative permittivity. These quantities have the unit dimension.

The SI system includes derived units with special names. These names are compact forms for representing combinations of base quantities. Let us give examples of units of the SI system that have their own names (Table 2).

Each quantity in the SI system has only one unit of measure, but the same unit of measure can be used for different quantities. Joule is a unit of measure for the amount of heat and work.

SI system, units of measurement multiples and submultiples

The International System of Units has a set of prefixes to units of measurement that are used if the numerical values ​​of the quantities in question are significantly greater or less than the unit of the system, which is used without a prefix. These prefixes are used with any unit of measure, in the SI system they are decimal.

We give examples of such prefixes (Table 3).

When writing, the prefix and the name of the unit are written together, so that the prefix and the unit of measure form a single character.

Note that the SI unit of mass (kilogram) historically already has a prefix. Decimal multiples and submultiples of the kilogram are obtained by adding the prefix to the gram.

Off-system units

The SI system is universal and is convenient in international communication. Almost all non-SI units can be defined using SI terms. The use of the SI system is preferred in science education. However, there are some quantities that are not included in the SI, but are widely used. Thus, units of time such as minutes, hours, days are part of the culture. Some units are used for historical reasons. When using units that do not belong to the SI system, it is necessary to indicate how they are converted to SI units. An example of units is shown in Table 4.