Temperature scale Fahrenheit, Celsius, Kelvin. Introduction: Temperature scales

Temperature is the most important parameter environment(OS). OS temperature characterizes the degree of heating, which is determined by the internal kinetic energy thermal movement of molecules. Temperature can be defined as a thermal state parameter. To compare the degree of heating of bodies, it uses a change in any of their physical properties that depends on temperature and is easily measurable (for example, volumetric expansion of a liquid, a change electrical resistance metal, etc.).

To proceed to the quantitative determination of temperature, it is necessary to establish a temperature scale, i.e. select the origin (zero temperature scale) and the unit of measurement for the temperature interval (degree).

Temperature scales used before the introduction of a single temperature scale are a series of marks within a temperature range limited by two easily reproducible constant (main reference or reference) boiling and melting points of chemically pure substances. These temperatures were taken equal to arbitrary numerical values ​​t" and t". Thus, 1 degree = (t" - t")/n, where t" and t" are two constant, easily reproducible temperatures; n is an integer into which temperature range.

To mark the temperature scale, the volumetric expansion of bodies when heated was most often used, and the boiling points of water and the melting of ice were taken as constant points. The temperature scales created by Lomonosov, Fahrenheit, Reaumur and Celsius are based on this principle. When constructing these scales, a linear relationship was assumed between the volumetric expansion of the liquid and temperature, i.e.

where k is the proportionality coefficient (corresponds to the relative temperature coefficient of volumetric expansion). Integrating equation (1) gives

where D is the integration constant.

To determine the constants k and D, two selected temperatures t" and t" are used. Taking volume V at temperature t" and volume V at temperature t" - V", we obtain

t" = kV" + D; (3)

t” = kV” + D; (4).

Subtracting equation (3) from equations (2) and (4), we obtain

t - t" = k(V - V") (5);

t” - t" = k(V” - V") (6).

Dividing equation (5) by equation (6), we get

where t" and t" are the temperatures of ice melting and water boiling, respectively, at normal pressure and free fall acceleration 980.665 cm/s 2 ; V" and V" - volumes of liquids corresponding to temperatures t" and t"; V is the volume of liquid corresponding to temperature t.

There are no liquids in nature with linear dependence between the coefficient of volumetric expansion and temperature, therefore, the readings of thermometers depend on the nature of the thermometric substance (mercury, alcohol, etc.).

With the development of science and technology, the need arose to create a unified temperature scale, unrelated to any particular properties of the thermometric substance and suitable over a wide temperature range. In 1848, Kelvin, based on the second law of thermodynamics, proposed determining temperature based on the equality

T 2 /(T 2 - T 1) = Q 2 /(Q 2 - Q 1),

where T 1 and T 2 are the temperatures of the refrigerator and heater, respectively; Q 1 and Q 2 are the amount of heat respectively received by the working substance from the heater and given to the refrigerator (for an ideal heat engine operating on the Carnot cycle).

Let T 2 be equal to the boiling point of water (T 100), and T 1 be the melting temperature of ice (T 0); then, taking the difference T 2 - T 1 equal to 100 degrees and denoting the amount of heat corresponding to these temperatures through Q 100 and Q 0, we obtain

T 100 = Q 100 100/(Q 100 - Q 0); T 0 = Q 0 100/(Q 100 - Q 0).

At any heater temperature

T = Q 100/(Q 100 - Q 0) (8).

The equation is an equation of the thermodynamic temperature scale, which does not depend on the properties of the thermometric substance.

The decision of the XI General Conference on Weights and Measures in Russia provided for the use of two temperature scales: thermodynamic and international practical.

In the thermodynamic Kelvin scale lowest point is the absolute zero point (0K), and the only experimental fundamental point is the triple point of water. This point corresponds to 273.16K. The triple point of water (the equilibrium temperature of water in the solid, liquid and gaseous phases) is your ice melting point at 0.01 degrees. The thermodynamic scale is called absolute if the point 273.16 K below the melting point of ice is taken as zero.

Strictly speaking, it is impossible to implement the Kelvin scale, because its equation is derived from the ideal Carnot cycle. The thermodynamic temperature scale coincides with the scale of a gas thermometer filled with an ideal gas. It is known that some real gases (hydrogen, helium, neon, nitrogen) in a wide temperature range differ in their properties relatively little from ideal gas. Thus, the scale of a hydrogen thermometer (taking into account corrections for the deviation of the properties of a real gas from an ideal one) is practically a thermodynamic temperature scale.

The International Practical Temperature Scale is based on a series of reproducible equilibrium states, which correspond to certain temperatures (main reference points), and on reference instruments calibrated at these temperatures. In the interval between the temperatures of the main reference points, interpolation is performed using formulas that establish a connection between the readings of standard instruments and the values ​​of the international practical scale. The main reference points are realized as certain states of phase equilibria of some pure substances and cover the temperature range from -259.34 0 C (triple equilibrium of hydrogen) to +1064.43 0 C (solidification point of gold).

The reference device used in the temperature range from -259.34 to +630.74 0 C is a platinum resistance thermometer, from +630.74 to +1064.43 0 C - a thermoelectric thermometer with thermoelectrodes and platinum rhodium (10% rhodium) and platinum. For the temperature range above 1064.43 0 C, the temperature on the international practical scale is determined in accordance with Planck’s law of radiation.

Temperature measured on the International Practical Scale is denoted by t, and the numerical values ​​are accompanied by the sign 0 C.

Temperature on the thermodynamic scale is related to temperature on the international practical scale by the ratio T = t + 273.15. At the IX General Conference on Weights and Measures in 1948, the international practical temperature scale was named the Celsius scale. The International Practical Temperature Scale and the Celsius scale have one constant point in common (the boiling point of water); at all other points these scales differ significantly, especially at high temperatures.

Annotation: The concept of scaling. Existing types scales and their areas of application. Reasons for the appearance of scales.

SHKA"LA, s, and. [latin. scala - ladder].- 1 . Ruler with divisions in different measuring instruments. W. thermometer. 2 . A series of quantities, numbers in ascending or descending order (special). Sh. the patient's temperature. Sh. diseases. Sh. salary.

Types of scales:

Measurement scales are usually classified according to the types of measured data, which determine the mathematical transformations acceptable for a given scale, as well as the types of relationships displayed by the corresponding scale. The modern classification of scales was proposed in 1946 by Stanley Smith Stevens.

Scale of names (nominal, classification)

Used to measure values qualitative signs. The value of such a feature is the name of the equivalence class to which the object in question belongs. Examples of the meanings of qualitative characteristics are names of states, colors, car brands, etc. Such characteristics satisfy the identity axioms:

At large number classes use hierarchical naming scales. Most famous examples Such scales are the scales used to classify animals and plants.

With values ​​measured in the scale of names, you can perform only one operation - checking their coincidence or non-coincidence. Based on the results of such a check, it is possible to additionally calculate filling frequencies (probabilities) for various classes that can be used for application various methods statistical analysis - Chi-square test of agreement, Cramer's test for testing the hypothesis about the relationship of qualitative characteristics, etc.

Ordinal scale (or rank scale)

Built on identity and order. Subjects in this scale are ranked. But not all objects can be subordinated to the relation of order. For example, it is impossible to say which is larger, a circle or a triangle, but one can identify a common property in these objects - area, and thus it becomes easier to establish ordinal relationships. For this scale, a monotonic transformation is acceptable. Such a scale is crude because it does not take into account the differences between the subjects of the scale. An example of such a scale: academic performance scores (unsatisfactory, satisfactory, good, excellent), Mohs scale.

Interval scale

Here there is a comparison with the standard. The construction of such a scale allows us to attribute most of the properties of existing numerical systems to numbers obtained on the basis of subjective assessments. For example, constructing an interval scale for reactions. For this scale, linear transformation is acceptable. This allows you to reduce test results to common scales and thus compare indicators. Example: Celsius scale.

Relationship scale

In the ratio scale, the relation “so many times more” applies. This is the only one of the four scales that has an absolute zero. The zero point characterizes the absence of the measured quality. This the scale allows similarity transformation (multiplication by a constant). Determining the zero point is a difficult task for research, imposing restrictions on the use of this scale. Using such scales, mass, length, strength, and value (price) can be measured. Example: Kelvin scale (temperatures measured from absolute zero, with the unit of measurement chosen by agreement of experts - Kelvin).

Difference scale

The starting point is arbitrary, the unit of measurement is specified. Acceptable transformations are shifts. Example: measuring time.

Absolute scale

It contains an additional feature - the natural and unambiguous presence of a unit of measurement. This scale has a single zero point. Example: number of people in the audience.

Of the scales considered, the first two are non-metric, and the rest are metric.

The issue of the type of scale is directly related to the problem of the adequacy of methods for mathematical processing of measurement results. In general, adequate statistics are those that are invariant with respect to admissible transformations of the measurement scale used.

Use in psychometrics. Using different scales, different psychological measurements can be made. The very first methods of psychological measurement were developed in psychophysics. The main task of psychophysicists was how to determine how the physical parameters stimulation and corresponding subjective assessments of sensations. Knowing this connection, you can understand what sensation corresponds to this or that sign. The psychophysical function establishes a connection between the numerical value of the scale physical dimension stimulus and the numerical value of the psychological or subjective response to this stimulus.

Celsius

1701 in Sweden. His areas of interest: astronomy, general physics, geophysics. He taught astronomy at Uppsala University and founded an astronomical observatory there.

Celsius was the first to measure the brightness of stars and establish the relationship between the northern lights and fluctuations in the Earth's magnetic field.

He took part in the Lapland expedition of 1736-1737 to measure the meridian. Upon returning from the polar regions, Celsius began active work on the organization and construction of an astronomical observatory in Uppsala and in 1740 became its director. Anders Celsius died on March 25, 1744. The mineral celsian, a type of barium feldspar, is named after him.

In technology, medicine, meteorology and in everyday life, the Celsius scale is used, in which the temperature of the triple point of water is 0.01, and therefore the freezing point of water at a pressure of 1 atm is 0. Currently, the Celsius scale is defined through the Kelvin scale: a degree Celsius is equal to a kelvin, . Thus, the boiling point of water, originally chosen by Celsius as a reference point equal to 100, has lost its value, and modern estimates boiling point of water at normal atmospheric pressure is about 99.975. The Celsius scale is practically very convenient because water is very common on our planet and our life is based on it. Zero Celsius is a special point for meteorology because it is associated with the freezing of atmospheric water. The scale was proposed by Anders Celsius in 1742.

Fahrenheit

Gabriel Fahrenheit. Daniel Gabriel Fahrenheit (1686–1736) - German physicist. Born on May 24, 1686 in Danzig (now Gdansk, Poland). He studied physics in Germany, Holland and England. He lived almost his entire life in Holland, where he was engaged in the manufacture of precision meteorological instruments In 1709 he made an alcohol thermometer, in 1714 - a mercury thermometer, using new way mercury purification. For mercury thermometer Fahrenheit constructed a scale with three reference points: corresponding to the temperature of the mixture water - ice - ammonia, - body temperature healthy person, and the value for the ice melting point was taken as the reference temperature. Boiling point clean water on the Fahrenheit scale was . The Fahrenheit scale is used in many English speaking countries, although it is gradually giving way to the Celsius scale. In addition to making thermometers, Fahrenheit was involved in improving barometers and hygrometers. He also studied the dependence of changes in the boiling point of a liquid on atmospheric pressure and the salt content in it, discovered the phenomenon of supercooling of water, and compiled tables specific gravity tel. Fahrenheit died in The Hague on September 16, 1736.

In England and especially in the USA, the Fahrenheit scale is used. Zero degrees Celsius is 32 degrees Fahrenheit, and a degree Fahrenheit is 5/9 degrees Celsius.

The following definition is currently accepted Fahrenheit scale: This is a temperature scale, 1 degree of which (1) is equal to 1/180 of the difference between the boiling point of water and the melting point of ice at atmospheric pressure, and the melting point of ice has a temperature of F. The Fahrenheit temperature is related to the Celsius temperature () by the ratio. Proposed by G. Fahrenheit in 1724.

Reaumur scale

Rene Reaumur. Rene Antoin de Reaumur was born on 28

February 1683 in La Rochelle, French naturalist, foreign honorary member of the St. Petersburg Academy of Sciences (1737). Works on regeneration, physiology, biology of insect colonies. He proposed a temperature scale named after him. He improved some methods of preparing steel, he was one of the first to make attempts to scientifically substantiate some casting processes, and wrote the work “The Art of Transforming Iron into Steel.” He came to a valuable conclusion: iron, steel, cast iron differ in the amount of some impurity. By adding this impurity to iron, by carburizing or alloying with cast iron, Reaumur obtained steel. In 1814, K. Careten proved that this impurity was carbon.

Reaumur gave a method for preparing frosted glass.

Today, memory associates his name only with the invention of a long

temperature scale used. In fact, René Antoine Ferchant de Reaumur, who lived in 1683-1757, mainly in Paris, was one of those scientists versatility which in our time - a time of narrow specialization - are difficult to imagine. Reaumur was at the same time a technician, physicist and natural scientist. He gained great fame outside of France as an entomologist. IN recent years During his life, Reaumur came to the idea that the search for the mysterious transformative power should be carried out in those places where its manifestation is most obvious - during the transformation of food in the body, i.e. upon its assimilation. He died on October 17, 1757 at the castle of Bermovdiere near Saint-Julien-du-Terroux (Mayenne).

Proposed in 1730 by R. A. Reaumur, who described the alcohol thermometer he invented.

The unit is the degree Reaumur (), equal to 1/80 of the temperature interval between the reference points - the temperature of melting ice () and boiling water ()

Currently, the scale has fallen out of use; it survived longest in France, the author’s homeland.

Comparison of temperature scales

Description	Kelvin	Celsius	Fahrenheit	Newton	Reaumur
Absolute zero	0	-273.15	-459.67	-90.14	-218.52
Melting temperature of a mixture of Fahrenheit (salt and ice in equal quantities)	255.37	-17.78	0	-5.87	-14.22
Freezing point of water (normal conditions)	273.15	0	32	0	0
Average human body temperature	310.0	36.8	98.2	12.21	29.6
Boiling point of water (normal conditions)	373.15	100	212	33	80
Solar surface temperature	5800	5526	9980	1823	4421

Temperature scales, systems of comparable numerical values ​​of temperature. Temperature is not a directly measurable quantity; its value is determined by the temperature change of any thermometric substance convenient for measuring the physical property. Having chosen a thermometric substance and property, it is necessary to set the initial reference point and the size of the temperature unit - degrees. Thus, empirical temperature scales (hereinafter referred to as T.s.) are determined. In T. sh. Usually, two main temperatures are recorded, corresponding to the points of phase equilibrium of one-component systems (the so-called reference or constant points), the distance between which is called the main temperature interval of the scale. The following reference points are used: the triple point of water, the boiling point of water, hydrogen and oxygen, the solidification point of silver, gold, etc. The size of a unit interval (temperature unit) is set as a certain fraction of the main interval. For the beginning of the counting T. sh. take one of the reference points. This is how you can determine the empirical (conditional) T. sh. for any thermometric property. If we assume that the relationship between and temperature is linear, then temperature , where , and are the numerical values ​​of the property at temperature , at the starting and ending points of the main interval, - the size of the degree, - the number of divisions of the main interval.

In the Celsius scale, for example, the temperature of water solidification (ice melting) is taken as the starting point; the main interval between the solidification and boiling points of water is divided into 100 equal parts ().

T. sh. is thus a system of successive temperature values ​​related linearly to the values ​​of the measured physical quantity (this quantity must be unambiguous and monotonic function temperature). In general, T. sh. may differ in thermometric property (this can be thermal expansion of bodies, change in electrical resistance of conductors with temperature, etc.), in thermometric substance (gas, liquid, solid), and also depend on reference points. In the simplest case, T. sh. differ in the numerical values ​​adopted for the same reference points. Thus, in the Celsius (), Reaumur () and Fahrenheit () scales, the melting points of ice and the boiling point of water at normal pressure are assigned different meanings temperature. Relationship for converting temperature from one scale to another:

Direct recalculation for T. sh., differing in basic temperatures, without additional experimental data is impossible. T. sh., differing in thermometric property or substance, are significantly different. An unlimited number of empirical thermometers that do not coincide with each other is possible, since all thermometric properties are related to temperature nonlinearly and the degree of nonlinearity is different for different properties and the real temperature measured according to the empirical thermometer is called conventional ("mercury", "platinum" temperature, etc.), its unit is the conventional degree. Among empirical T. sh. special place occupy gas scales in which gases serve as thermometric substances ("nitrogen", "hydrogen", "helium" thermometer). These T. sh. depend less than others on the gas used and can be (by introducing corrections) brought to the theoretical gas T. sh. Avogadro, valid for an ideal gas. Absolute empirical T. sh. They call a scale, the absolute zero of which corresponds to the temperature at which the numerical value of a physical property (for example, in the Avogadro gas theory, the absolute zero of temperature corresponds to the zero pressure of an ideal gas). temperatures (according to the empirical T. sh.) and (according to the absolute empirical T. sh.) are related by the relation , where is the absolute zero of the empirical T. sh. (the introduction of absolute zero is an extrapolation and does not imply its implementation).

The fundamental drawback of empirical T. sh. - their dependence on the thermometric substance - is absent in thermodynamic theory, based on the second law of thermodynamics. When determining the absolute thermodynamic temperature. (Kelvin scale) come from the Carnot cycle. If in the Carnot cycle a body completing the cycle absorbs heat at temperature and releases heat at temperature , then the ratio does not depend on the properties of the working fluid and allows one to determine the absolute temperature using the quantities available for measurements. Initially, the main interval of this scale was set by the points of melting ice and boiling water at atmospheric pressure, the unit of absolute temperature corresponded to part of the main interval, and the point of melting ice was taken as the starting point. In 1954, the X General Conference on Weights and Measures established the thermodynamic T. sh. with one reference point - the triple point of water, the temperature of which is taken to be 273.16 K (exactly), which corresponds to . temperature in absolute thermodynamic T. sh. measured in kelvins (K). The thermodynamic temperature scale, in which the temperature is taken for the melting point of ice, is called centigrade. Relationships between temperatures expressed in Celsius and absolute thermodynamic T. scale:

so the size of the units in these scales is the same. In the USA and some other countries where it is customary to measure temperature on the Fahrenheit scale, absolute T. sh. Rankin. The relationship between kelvin and degree Rankine: , on the Rankine scale, the melting point of ice corresponds to , boiling point of water .

Any empirical T. sh. is reduced to thermodynamic T. sh. introduction of corrections taking into account the nature of the relationship between the thermometric property and thermodynamic temperature. Thermodynamic T. sh. is carried out not directly (by performing a Carnot cycle with a thermometric substance), but with the help of other processes associated with thermodynamic temperature. In a wide temperature range (approximately from the boiling point of helium to the solidification point of gold), thermodynamic T. sh. coincide with T. sh. Avogadro, so the thermodynamic temperature is determined by the gas temperature, which is measured with a gas thermometer. With more low temperatures ah thermodynamic T. sh. carried out according to the temperature dependence of the magnetic susceptibility of paramagnetic materials, at higher values ​​the scale was redefined several times (MTSh-48, MPTS-68, MTSH-90): reference temperatures and interpolation methods changed, but the principle remained the same - the basis of the scale is a set of pure phase transitions substances with certain values ​​of thermodynamic temperatures and interpolation instruments calibrated at these points. The ITS-90 scale is currently in effect. The main document (Regulations on the scale) establishes the definition of Kelvin, the values ​​of phase transition temperatures (reference points) and interpolation methods.

Temperature scales used in everyday life - both Celsius and Fahrenheit (used mainly in the USA) - are not absolute and therefore inconvenient when conducting experiments in conditions where the temperature drops below the freezing point of water, which is why the temperature must be expressed negative number. For such cases, absolute temperature scales were introduced.

One of them is called the Rankine scale, and the other is the absolute thermodynamic scale (Kelvin scale); their temperatures are measured in degrees Rankine () and kelvins (K), respectively. Both scales begin at absolute zero temperature. They differ in that Kelvin equal to a degree Celsius, and the Rankine degree is the Fahrenheit degree. The freezing point of water at standard atmospheric pressure corresponds to , , .

The Kelvin scale is tied to the triple point of water (273.16 K), and the Boltzmann constant depends on it. This creates problems with the accuracy of interpretation of high temperature measurements. The BIPM is now considering the possibility of moving to a new definition of Kelvin and fixing the Boltzmann constant, instead of reference to the triple point temperature.

Brief summary: the student became familiar with the classification of scales and their scope.

Practice kit

Questions:

1. When and by whom was the modern classification of scales proposed?
2. Define the word SCALE.
3. List all the types of scales you know and explain their differences?
4. Why are scales used in psychometrics?
5. Which scales are most used in England and America?
6. Which of the above scales appeared first?
7. Which country has used the Reaumur scale for the longest time?
8. How is temperature measured on the absolute thermodynamic temperature scale?
9. Give examples of absolute temperature scales.
10. What is the relationship between kelvin and degree Rankine?

Exercises

1. Draw a diagram showing modern classification scales Can you create scales according to hierarchy?
2. Determine the temperature value in different temperature scales (Fahrenheit, Kelvin)

Measurement of thermal energy quantities

One of the most important thermal energy quantities is temperature. Temperature is a physical quantity that characterizes the degree of heating of a body or its thermal energy potential. Almost everything technological processes and various properties of a substance depend on temperature.

Unlike such physical quantities as mass, length, etc., temperature is not an extensive (parametric), but an intensive (active) quantity. If a homogeneous body is divided in half, then its mass is also divided in half. Temperature, being an intensive quantity, does not have this property of additivity, i.e. For a system in thermal equilibrium, every part of the system has the same temperature. Therefore, it is not possible to create a temperature standard, just as standards of extensive quantities are created.

Temperature can only be measured indirectly, based on the temperature dependence of such physical properties bodies that can be directly measured. These properties of bodies are called thermometric. These include length, density, volume, thermoelectric power, electrical resistance, etc. Substances characterized by thermometric properties are called thermometric. The instrument for measuring temperature is called a thermometer. To create a thermometer, you must have a temperature scale.

The temperature scale is a specific functional numerical relationship between temperature and the values ​​of the measured thermometric property. In this regard, it seems possible to construct temperature scales based on the choice of any thermometric property. At the same time, there is no general thermometric property that is linearly related to temperature changes and does not depend on other factors over a wide range of temperature measurements.

The first temperature scales appeared in the 18th century. To construct them, two reference points t 1 and t 2 were selected, representing the phase equilibrium temperatures of pure substances. The temperature difference t 2 - t 1 is called main temperature range. The German physicist Gabriel Daniel Fahrenheit (1715), the Swedish physicist Anders Celsius (1742) and the French physicist René Antoine Reaumur (1776) when constructing scales were based on the assumption of a linear relationship between temperature t and thermometric property, which was used as expansion of the volume of liquid V, i.e.

t = a + bV, (1)

Where A And b– constant coefficients.

Substituting V = V 1 at t = t 1 and V = V 2 at t = t 2 into this equation, after transformation we obtain the temperature scale equation:

In the Fahrenheit, Reaumur and Celsius scales, the melting point of ice t 1 corresponded to +32 0, 0 0 and 0 0, and the boiling point of water t 2 - 212 0, 80 0 and 100 0. The main interval t 2 - t 1 in these scales is divided respectively into N = 180, 80 and 100 equal parts, and the 1/N part of each interval is called the Fahrenheit degree - t 0 F, the Reaumur degree t 0 R and the Celsius degree t 0 C Thus, for scales constructed according to this principle, the degree is not a unit of measurement, but represents a unit interval - the scale of the scale.

To convert temperature from one scale to another, use the following ratio:

(3)

Later it was found that the readings of thermometers with different thermometric substances (mercury, alcohol, etc.), using the same thermometric property and a uniform degree scale, coincide only at reference points, and at other points the readings diverge. The latter is especially noticeable when measuring temperatures whose values ​​are located far from the main interval.

This circumstance is explained by the fact that the relationship between temperature and thermometric property is actually nonlinear and this nonlinearity is different for different thermometric substances. In particular, the nonlinearity between temperature and change in liquid volume is explained by the fact that the temperature coefficient of volumetric expansion of the liquid itself changes with temperature and this change is different for different droplet liquids.

Based on the described principle, you can build any number of scales that differ significantly from each other. Such scales are called conventional, and the scales of these scales are called conventional degrees.

The problem of creating a temperature scale independent of the thermometric properties of substances was solved in 1848 by Kelvin, and the scale he proposed was called thermodynamic. Unlike conventional temperature scales, the thermodynamic temperature scale is absolute.

Thermodynamic temperature scale based on the use of the second law of thermodynamics. In accordance with this law, the coefficient useful action h of a heat engine operating on a reverse Carnot cycle is determined only by the temperature of the heater T n and the refrigerator T x and does not depend on the properties of the working substance:

(4)

where Q n and Q x are, respectively, the amount of heat received by the working substance from the heater and given to the refrigerator.

Kelvin proposed to use the equality to determine temperature

Therefore, by using one object as a heater and another as a refrigerator and running a Carnot cycle between them, it is possible to determine the temperature ratio of the objects by measuring the ratio of heat taken from one object and given to the other. The resulting temperature scale does not depend on the properties of the working substance and is called the absolute temperature scale. To absolute temperature had a certain significance, it was proposed to take the difference in thermodynamic temperatures between the boiling points of water T kv and the melting points of ice T tl equal to 100 0. The acceptance of such a difference pursued the goal of maintaining continuity numerical value thermodynamic temperature scale from the centigrade Celsius temperature scale. T.O., denoting the amount of heat received from the heater (boiling water) and given to the refrigerator (melting ice), respectively, through Q kv and Q tl, and taking T kv - T tl = 100, we obtain:

And (6)

For any temperature T of the heater, with a constant value of T tl of the refrigerator and the amount of heat Q t given to it by the working substance of the Carnot machine, we will have:

(7)

Equation (6) is the equation centigrade thermodynamic temperature scale and shows that the temperature value T on this scale is linearly related to the amount of heat Q received by the working substance of a heat engine when it performs a Carnot cycle, and, as a consequence, does not depend on the properties of the thermodynamic substance. One degree of thermodynamic temperature is taken to be the difference between the body temperature and the melting temperature of ice at which the work performed in the reverse Carnot cycle is equal to 1/100 of the work done in the Carnot cycle between the boiling point of water and the melting temperature of ice (provided that in both cycles the amount of heat given off to the refrigerator is the same).

From the definition of efficiency it follows that at the maximum value h=1 T x should be equal to zero. This lowest temperature was called absolute zero by Kelvin. Temperature on the thermodynamic scale is designated “K”.

The thermodynamic temperature scale, based on two reference points, has insufficient measurement accuracy. Almost difficult to reproduce temperatures specified points, because they depend on pressure, as well as on the salt content in the water. Therefore, Kelvin and Mendeleev expressed the idea of ​​the feasibility of constructing a thermodynamic temperature scale based on one reference point.

Thermometry Advisory Committee International Committee Weights and Measures in 1954 adopted a recommendation to move to the definition of a thermodynamic scale using one reference point - the triple point of water (the equilibrium point of water in the solid, liquid and gaseous phases), which is easily reproduced in special vessels with an error of no more than 0.0001 K The temperature of this point is taken to be 273.16 K, i.e. higher than the melting temperature of ice by 0.01 K. This number was chosen so that the temperature values ​​​​on the new scale practically do not differ from the old Celsius scale with two reference points. The second reference point is absolute zero, which is practically not realized, but has a strictly fixed position.

In 1967 XIII General Assembly on weights and measures clarified the definition of the unit of thermodynamic temperature in the following wording: “ Kelvin– 1/273.16 part of the thermodynamic temperature of the triple point of water.” Thermodynamic temperature can also be expressed in degrees Celsius:

t = T– 273.15 K (8)

The most famous at the moment, temperature scales are Fahrenheit, Celsius and Kelvin.

Fahrenheit temperature scale most popular in the USA. Temperature is measured in degrees, for example 48.2°F (forty-eight point two degrees Fahrenheit), the symbol F indicates that the Fahrenheit scale is used.

Europeans are accustomed to Celsius temperature scale, which also measures temperature in degrees, for example 48.2°C (forty-eight point two degrees Celsius), the symbol C indicates that the Celsius scale is used.

Scientists are more accustomed to operating with Kelvin temperature scale. Until 1968, kelvin was officially called the Kelvin degree, then it was decided to name the temperature value measured on the Kelvin scale simply in kelvins (without degrees), for example, 48.2 K (forty-eight and two kelvins).

Daniel Gabriel Fahrenheit invented his scale in the 18th century while making thermometers in Amsterdam. Fahrenheit took the temperature of a frozen salt solution, which at that time was used to obtain low temperatures in laboratory conditions, as the zero temperature point. The German physicist set the value of 32°F for the melting point of ice and the freezing point of water (with increasing and decreasing temperatures, respectively). According to the resulting scale, the boiling point of water is 212°F.

In the same 18th century, a Swedish scientist Anders Celsius invented his own temperature scale, which is based on the freezing point (0°C) and boiling point (100°C) of pure water at normal atmospheric pressure.

The Kelvin scale was invented in the 19th century by a British scientist William Thomson, who subsequently received the honorary title of Baron Kelvin. Thomson based his temperature scale on the concept of absolute zero. Later, the Kelvin scale became the main one in physics, and now the Fahrenheit and Celsius systems are determined through it.

At its core, the temperature of any object characterizes the measure of movement of its molecules - the faster the molecules move, the higher the temperature of the object, and vice versa. The lower the temperature, the slower the molecules move. At absolute zero (0 K), the molecules stop (which cannot happen in nature). For this reason, it is impossible to reach absolute zero or even lower temperatures.

It must be said that the graduations of the Kelvin and Celsius scales are the same (one degree Celsius is equal to one kelvin), and 0 K = -273.15°C.

Thus, linking the Kelvin and Celsius temperature scales is very simple:

K = C+273.15 C = K-273.15

Let's try to connect the Celsius and Fahrenheit scales.

As you know, water freezes at 32°F and 0°C: 32°F=0°C. Water boils at 212°F and 100°C: 212°F=100°C.

Thus, for 180 degrees Fahrenheit there are 100 degrees Celsius (9/5 ratio): 212°F-32°F=100°C-0°C.

It should also be noted that the zero point of the Celsius scale corresponds to the 32-degree point of the Fahrenheit scale.

Taking into account the above correspondences between the two scales, we derive the formula for converting temperature from one scale to another:

C = (5/9) (F-32) F = (9/5) C+32

If you decide this system equations, we can find out that -40°C = -40°F- this is the only temperature at which the values ​​of both scales coincide.

Proceeding in a similar way, we connect the Kelvin and Fahrenheit scales:

F = (9/5)·(K-273.15)+32 = (9/5)K-459.67 K = (5/9)·(F+459.67)

Temperature and temperature scales

Temperature - degree of heating of the substance. This concept based on the ability to transfer heat by different bodies (substance) to each other at different degrees of their heating and to be in a state thermal equilibrium at equal temperatures. Moreover, heat is always transferred from the body with more high temperature to a body with low temperature. Temperature can also be defined as a parameter of the thermal state of a substance, determined by the average kinetic energy of movement of its molecules. From here it is obvious that the concept of “temperature” is inapplicable for one molecule, because at any particular temperature the energy of one molecule cannot be characterized by an average value. From this provision It follows that the concept of “temperature” is statistical.

Temperature is measured by instruments called thermometers, the basis of which can be based on various physical principles. The ability to measure temperature with such devices is based on the phenomenon of thermal exchange between bodies and to varying degrees heating and changes in their physical (thermometric) properties during heating (cooling).

To quantify temperature, it is necessary to choose one or another temperature scale. Temperature scales are built on the basis of certain physical properties of a substance, which should not depend on extraneous factors and should be accurately and conveniently measured. In fact, there is not a single thermometric property for thermometric bodies or substances that would completely satisfy the specified conditions over the entire range of measured temperatures. Therefore, temperature scales are defined for different temperature ranges, based on the arbitrary assumption of a linear relationship

between the property of a thermometric body and temperature. Such scales are called conditional and the temperature measured by them -conditional.

4 The conventional temperature scale includes one of the most common scales - the Celsius scale. According to this scale, the melting points of ice and the boiling point of water at normal atmospheric pressure are taken as the boundaries of the conditional measurement range, and one hundredth of this scale is usually called one degree Celsius (\ WITH),

| However, constructing such a temperature scale without using liquid thermometers can lead to a number of difficulties associated with the properties of the thermometric liquids used. For example, the readings of mercury and alcohol thermometers operating on the principle of liquid expansion will be different when measuring the same temperature due to different coefficients of their volumetric expansion.

| Therefore, to improve the conventional temperature scale, it was proposed to use a gas thermometer using gases whose properties would differ slightly from the properties of an ideal gas (hydrogen, helium, nitrogen, etc.).

Using a gas thermometer, temperature measurement can be based on changes in the volume or pressure of gas in a closed thermal system.

In practice, a method based on measuring pressure at a constant volume has become more widespread, because is more accurate and easy to implement.

To create a single temperature scale that is not related to thermometric properties various substances for a wide temperature range, Kelvin proposed a temperature scale based on the second law of thermodynamics. This scale is called thermodynamic temperature scale.

It is based on the following provisions:

If, during a reversible Carnot cycle, a body absorbs heat 0, at temperature T, and releases heat C? 3 at temperature T 2, then the following equality must be observed:

THAT,

n<Г (21)

According to the principles of thermodynamics, this ratio does not depend on the properties of the working fluid.

I The Kelvin thermodynamic temperature scale began to be used as the initial scale for other temperature scales that do not depend on the thermometric properties of the working substance. To determine one degree on this scale, the interval between the melting points of ice and the boiling point of water is divided, as in the centigrade Celsius scale, into one hundred equal parts. Thus, I П С turns out to be equal to ] °К

* According to this scale, commonly called absolute The zero point is taken to be a temperature 273.15° below the melting point of ice, called absolute zero. It has been theoretically proven that at this temperature all thermal movement of the molecules of any substance ceases, therefore this scale is to a certain extent theoretical in nature.

The following relationship applies between temperature T, expressed in Kelvin, and temperature *, expressed in degrees Celsius:

1=T-T 0 , (2.2)

where T 0 = 273.15 K.

Of the existing thermometers, gas thermometers most accurately implement the absolute temperature scale in the range of no higher than 1200 °C. The use of these thermometers at higher temperatures faces great difficulties; in addition, gas thermometers are quite complex and bulky devices, which is inconvenient for practical purposes. Therefore, for the practical and convenient reproduction of the thermodynamic scale in wide ranges of temperature changes, International practical

temperature cabinets (MPTS). Currently, the MPTS-68 temperature scale, adopted in 1968, is in force, the construction of which is based on reference points determined by the phase state of substances. These reference points are used to standardize temperatures in various ranges, which are given in table. 2.1.