The concept of physical quantity. The meaning of systems of physical units. Determination of a physical quantity
A physical quantity is a concept of at least two sciences: physics and metrology. By definition, a physical quantity is a certain property of an object or process, common to a number of objects in terms of qualitative parameters, but differing, however, in quantitative terms (individual for each object). A classic example of illustrating this definition is the fact that, having their own mass and temperature, all bodies have individual numerical values of these parameters. Accordingly, the size of a physical quantity is considered to be its quantitative content, content, and in turn, the value of a physical quantity is a numerical estimate of its size. In this regard, there is the concept of a homogeneous physical quantity when it is the bearer of a similar property in qualitatively. Thus, obtaining information about the values of a physical quantity as a certain number of units accepted for it is the main task measurements. And, accordingly, a physical quantity, which by definition is assigned a conditional value, equal to one, is a unit of physical quantity. In general, all values of physical quantities are traditionally divided into: true and real. The first are values that ideally reflect in qualitative and quantitative terms the corresponding properties of the object, and the second are values found experimentally and so close to the truth that they can be accepted instead. However, the classification of physical quantities does not end there. There are a number of classifications created according to various criteria. The main ones are divided into:
1) active and passive physical quantities - when divided in relation to measurement information signals. Moreover, the first (active) in this case are quantities that, without the use of auxiliary energy sources, have the probability of being converted into a measurement information signal. And the second (passive) are quantities for which it is necessary to use auxiliary energy sources that create a signal of measurement information;
2) additive (or extensive) and non-additive (or intensive) physical quantities - when dividing on the basis of additivity. It is believed that the first (additive) quantities are measured in parts; in addition, they can be accurately reproduced using a multivalued measure based on the summation of the sizes of individual measures. But the second (non-additive) quantities are not directly measured, since they are converted into a direct measurement of a quantity or a measurement by indirect measurements.
In 1791 G. The French National Assembly adopted the first ever system of units of physical quantities. It was a metric system of measures. It included: units of length, area, volume, capacity and weight. And they were based on two now well-known units: the meter and the kilogram. A number of researchers believe that, strictly speaking, this first system is not a system of units in the modern sense. And only in 1832, the German mathematician K. Gauss developed and published the latest methodology for constructing a system of units, which in this context is a certain set of basic and derived units.
The scientist based his methodology on three main independent quantities: mass, length, time. And the mathematician took the milligram, millimeter and second as the main units of measurement for these quantities, since all other units of measurement can be easily calculated using the minimum ones. K. Gauss considered his system of units to be an absolute system. With the development of civilization and scientific and technological progress, a number of systems of units of physical quantities arose, the basis for which is the principle of the Gaussian system. All of these systems are constructed as metric systems, but they are distinguished by different base units. Thus, at the present stage of development, the following main systems of units of physical quantities are distinguished:
1) GHS system(1881) or the CGS System of Units of Physical Quantities, the basic units of which are the following: centimeter (cm) - represented as a unit of length, gram (g) - as a unit of mass, and second (s) - as a unit of time ;
2) MKGSS system(end of the 19th century), initially using the kilogram as a unit of weight, and subsequently as a unit of force, which led to the creation of a system of units of physical quantities, the main units of which were three physical units: the meter as a unit of length, the kilogram-force as a unit of force and the second as unit of time;
3) MKSA system(1901), the foundations of which were created by the Italian scientist G. Giorgi, who proposed the meter, kilogram, second and ampere as units of the MCSA system.
Today in world science there are an innumerable number of various systems of units of physical quantities, as well as many so-called non-systemic units. This, of course, leads to certain inconveniences in calculations, forcing one to resort to recalculation when converting physical quantities from one system of units to another. A situation has arisen in which there is a serious need to unify units of measurement. It was necessary to create a system of units of physical quantities that would be suitable for most different branches of the measurement field. Moreover, the main emphasis should have been the principle of coherence, implying that the unit of the proportionality coefficient is equal in the equations of the relationship between physical quantities. A similar project was created in 1954 by a commission to develop a unified International System of Units. It was called the "Draft International System of Units" and was eventually approved by the General Conference on Weights and Measures. Thus, the system based on seven basic units came to be called the International System of Units, or SI for short, which comes from the French abbreviation “Systeme International” (SI). International system units, or SI for short, contains seven basic, two additional, as well as several non-systemic, logarithmic units of measurement, which can be seen in Table 1.
Classification of physical quantities.
Classification of units of physical quantities.
SECTION 1. METROLOGY. Topic 3
Topic 3. Physical quantities as an object of measurement. SI system (SI)
Study questions:
1. Determination of a physical quantity.
2. International system of units of physical quantities SI.
Physical quantity (PV) is a property of a physical object that is common to many objects in a qualitative sense (this is a type of quantity), but individual in a quantitative sense (this is the size of a quantity).
System– are included in one of the accepted systems (these are all basic, derivative, multiple and submultiple units).
Off-system– are not included in any of the accepted systems of PV units (liter, nautical mile, carat, horsepower).
Multiple is a unit of physical activity, the value of which is an integer number of times greater than a system or non-system unit (for example, a unit of length 1 km = 103 m, that is, a multiple of a meter).
Dolnaya- this is a unit of PV, the value of which is an integer number of times less than a systemic or non-systemic unit (for example, a unit of length 1 mm = 10-3m, that is, it is a submachine unit).
Basic quantities are independent of each other and serve as the basis for establishing connections with other physical quantities, which are called derivatives from them. For example, in Einstein's formula E=mc2, mass is the basic unit and energy is the derived unit.
The set of basic and derived units is called a system of units of physical quantities. In 1960, the International System of Units (Systeme International d'Unites), designated SI, was adopted. It contains basic (meter, kilogram, second, ampere, kelvin, mole, candela), additional and derivative (radian, steradian) units of physical quantities .
In science, technology and everyday life, people deal with various properties of the physical objects around us. Their description is made using physical quantities.
Physical quantity (PV) is a property of a physical object that is common to many objects in a qualitative sense (this is a type of quantity - R), but individual in a quantitative sense (this is the size of a quantity - 10 Ohms).
In order to be able to establish for each object differences in the quantitative content of the property reflected by the physical quantity, the concepts of its size and value were introduced in metrology.
The size of the PV is the quantitative content in this object properties corresponding to the concept of PV - all bodies differ in mass, i.e. according to the size of this FV.
The PV value is an estimate of its size in the form of a certain number of units accepted for it. It is obtained as a result of measuring or calculating EF.
A PV unit is a PV of a fixed size, which is conditionally assigned a numerical value equal to 1.
Example: PV - mass,
the unit of this PV is 1 kg.
value - object mass = 5 kg.
A system of physical quantities is a set of interrelated physical quantities, formed in accordance with selected principles, when some quantities are taken as independent (basic), while others are functions (derivatives) of independent quantities.
Basic physical quantities do not depend either on each other or on other quantities of this system.
Independent quantities that do not have governing equations are called “fundamental physical quantities.” (As an example of basic physical quantities, let us name quantities such as distance and time.) And quantities that are determined using governing equations are called “derived physical quantities.”
specific value is a value divided by mass (for example, specific volume);
A molar quantity is a quantity divided by the amount of a substance (for example, molar volume).
4. What is a physical quantity? Classification of fw by types of phenomena.
According to the types of phenomena, physical quantities are divided into the following groups:
Material, that is, describing the physical and physico-chemical properties of substances, materials and products made from them. This group includes mass, density, electrical resistance, capacitance, inductance, etc. Sometimes these physical quantities are called passive. To measure them, it is necessary to use an auxiliary energy source, with the help of which a measurement information signal is generated. In this case, passive physical quantities are converted into active ones, which are measured;
Energy, that is, quantities that describe 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 signals.
5. What is a physical quantity? Classification of PVs according to their belonging to different groups of physical processes.
Physical quantity is a physical property of a material object, physical phenomenon, process that can be characterized quantitatively.
According to affiliation various groups physical processes, physical quantities are divided into spatiotemporal, mechanical, thermal, electrical and magnetic, acoustic, light, physicochemical, ionizing
radiation, atomic and nuclear physics.
6. What is a standard unit of physical quantity? What types of standards do you know?
A standard of a unit of physical quantity is a measuring instrument (or a set of measuring instruments) intended for reproducing and (or) storing a unit and transferring its size to subordinate measuring instruments in the verification scheme and approved as a standard in the prescribed manner.
Primary standard is a standard that reproduces a unit of physical quantity with the highest accuracy possible in a given field of measurement at the current level of scientific and technical achievements. The primary standard can be national (state) and international.
Secondary standard - a standard that receives the size of a unit directly from the primary standard of a given unit.
Standard of comparison - a standard used for comparisons of standards that, for one reason or another, cannot be directly compared with each other.
Original standard - a standard that has the highest metrological properties (in a given laboratory, organization, enterprise), from which the unit size is transmitted to subordinate standards and available measuring instruments.
Working standard - a standard designed to convey the size of a unit to working measuring instruments.
State primary standard - the primary standard, recognized by the decision of the authorized state body as the initial standard on the territory of the state.
National standard - a standard recognized by an official decision to serve as a reference for a country.
International standard - a standard adopted by international agreement as an international basis for harmonizing with it the sizes of units reproduced and stored by national standards.
What is measurement?
Measurement
Quantities.
Physical quantity
Units of physical quantities
Unit
Define the true value of a quantity, real and measured.
Measured value
Real value- this is a value found experimentally and so close to it that it can be used instead of the true one.
True meaning
List metric and non-metric scales, what is their difference?
1. Names (non-metric. Reflects the ordering of qualitative properties, characterized by the action of equivalence)
2. Order (non-meter. Represents a ranked series - a sequence of quantities, ordered in ascending or descending order, characterizing the property being studied)
3. Differences (Intervals) (Transitional non-meter-meter. Differs from the order scale in that for variable quantities not only order relations are introduced, but also summations of intervals (differences) between quantitative manifestations of properties.)
4. Relation (Metric describes the properties of quantities for which the relations of order, summation of intervals and proportionality are applicable)
5. Absolute (Meter has all the features of a ratio scale, but in addition there is a natural unambiguous definition of the unit of measurement)
6. Logarithmic (non-meter. Often used in practice)
7. Biological (non-metric. Ecological scale, reactions and the physical factors affecting them are described)
B. Name the principles for constructing the modern International System of Units of Quantities.
Principles of K. Gauss: (1832)
1. All physical quantities are divided into two groups - basic and derivative
2. Definition units basic quantities.
3. For other derived quantities, the units are derived on the basis of fundamental laws.
List the units of basic physical quantities, give their designation and dimension.
Basic SI units
8. Define the standard unit of physical quantity. Name the hierarchy
standards?
What is a verification scheme?
Verification diagram for measuring instruments- a normative document establishing the subordination of measuring instruments involved in transferring the unit size from the standard to working measuring instruments (indicating methods and errors during transmission). Distinguish state And local verification diagrams, previously there were also departmental PV
State PS applies to all measuring instruments of a given physical quantity used in the country, for example, measuring instruments electrical voltage in a certain frequency range. Local verification schemes apply to measuring instruments subject to verification in a given metrological department at an enterprise that has the right to verify measuring instruments and are issued in the form of an enterprise standard.
How does the measured value of a quantity differ from the true value?
Measured value is an experimental result obtained in an experiment with established accuracy.
True meaning– this is a value ideally reflected in qualitative and quantitative relationships of the corresponding properties of an object.
Define the error of the measurement result and the error of the means
Measurements.
Measurement result error(or measurement error) is the deviation of the measurement result from the true measurement from the true value of the measured value,
Measuring instrument error- the difference between the reading of the measuring instrument and the true value of the measured physical quantity.
Is it being assessed?
Non-excluded systematic error is formed from components, which can be non-excluded errors of the method, measuring instruments, subjective errors
Remedy:
Method of comparison with measure (substitution of opposition)
Sign compensation method
Randomization method (measuring a value using various thetodes or instruments)
MEASURING TOOLS
1. How do measuring instruments differ from indicators?
Technological measuring instruments a device that stores the PV unit, has a device for comparing it with the property of the object and has metrological characteristics. Along with measuring instruments, technical indicators are used. devices that do not have metrological characteristics, their task is to indicate that this PV is present here, do not pass the test procedure.
2. Give a definition and metrological classification of measuring instruments.
Technological measuring instruments a device that stores the PV unit, has a device for comparing it with the property of the object and has metrological characteristics.
1) SI type (determines the measured PV)
2) Type of measuring instrument (determined by the physical principle underlying the measuring instrument, design, technical conditions, document): measures, measuring transducers, instruments, installations, systems, complexes.
3) Metrological purpose: working measuring instruments (measurement) and working standards (verification or calibration of working measuring instruments).
3. What are reference materials and what are they used for?
A standard sample RM (refers to measures) is a sample of a substance (material) with the values of one or more quantities established as a result of metrological certification, characterizing the composition or property of this substance (material). (Certificate of composition and properties; State Certification of GSO and Certification of enterprises SOP). Used to determine the rights of a device or material.
4. What is the difference between a measuring transducer and a measuring device?
Measuring transducers are SI that produce a signal of measuring information in a form convenient for conversion, transmission, storage and processing, but inaccessible to perception.
The measuring device is C, designed to generate signals in a form accessible to perception.
5. Define the concept of “unity of measurements”.
Unity of measurements is the state of measurements in which the results are expressed in units approved for use, and the measurement accuracy readings do not go beyond the established limits (error standards).
6. Indicate the purpose of the metrological characteristics of measuring instruments,
A. classify them.
MX are characteristics that determine the measurement result and the amount of permissible error.
1) The result of the characteristic is specified by: a) the range of readings of changes (start and end points of the device); b) the value of scale division (the difference in the values of two adjacent scale marks on measuring transducers), the conversion function belongs to this group.
2) MX, defining errors: a) main, b) additional, c) dynamic.
7. Define the main and additional errors of measuring instruments.
The main error is established in tests under normal conditions (t=(20+-5)С, pressure 1 atm, humidity (65+-15)%, voltage 220 V +-10.
An additional error is established in tests when the environment changes. environment under conditions other than normal.
8. Specify the purpose of the conversion function and methods of its representation.
The conversion function Y=f(X) is the main characteristic of SI for static measurements. It establishes the functional dependence of the informative parameter of the output signal Y on the informative parameter input signal X SI. Presented in the form of a formula, graph or table.
9. Define the concept of “accuracy class” and indicate its purpose.
Accuracy class is a generalized characteristic of errors, determined by the limit of permissible values of the main and additional errors. Allows standardization measuring instruments, to facilitate the choice of measuring instruments, to make an approximate assessment of the measurement accuracy. When determining the accuracy class, the limits of the permissible main error are normalized, and in some cases, together with the main one, the limits of the permissible additional error are normalized.
10. Why is it necessary to carry out the verification or calibration procedure for measuring instruments? What is needed for this procedure?
To ensure the operation of the SI, periodic verification of the SI error is provided. To do this you need to conduct an experiment.
Calibration is a set of operations performed in order to determine the actual values of the MX SI.
Verification is a set of operations performed to confirm compliance of measuring instruments with metrological requirements (in the areas of state control).
To organize verification, it is necessary to have a working standard and a laboratory with normal conditions, a specialist (verifier).
LEGISLATIVE METROLOGY
Measurements?
Carried out for:
1. Compliance with mandatory requirements in the field of state regulation to ensure the uniformity of measurements for measurements, units of quantities, standards of units of quantities, standard samples, measuring instruments.
2. Availability and compliance with certified measurement techniques (methods).
3. Compliance with mandatory requirements for packaged goods.
Is it used?
determination and establishment of compliance of the metrological characteristics of measuring instruments with the requirements of the documents applicable to them, indicating the obtained data in the certificate; establishing a list of metrological characteristics of measuring instruments subject to control during verification; testing of verification methods.
What is measurement?
Measurement– is a set of operations for application technical means, storing a unit of a physical quantity, ensuring the determination of the relationship (explicitly or implicitly) of the measured quantity, ensuring the determination of the relationship (explicitly or implicitly) of the measured quantity with its unit and obtaining the value of this quantity
Give a definition of the concept of “physical quantity” and physical unit
Quantities.
Physical quantity– one of the properties of a physical object ( physical system, phenomenon or process), common in qualitative terms for many physical objects, but quantitatively individual for each of them.
Units of physical quantities– create the possibility of quantitative assessment; without them it is not possible to perform measurements. In our country, Spanish. International System of Units SI. (Required by law in 1993)
Unit– is a quantity of a fixed size, which is conventionally assigned a numerical value equal to 1, and is used for the quantitative expression of physical quantities similar to it. A unit of measurement may belong to any system of units or be non-systemic (or) conventional. Obviously, the numerical value of a quantity directly depends on the chosen unit of measurement.