Temperature dimension. Temperature detection

Every person is faced with the concept of temperature every day. The term has firmly entered our daily life: we heat food in the microwave or cook food in the oven, we are interested in the weather outside or find out if the water in the river is cold - all this is closely related to this concept. And what is temperature, what does this physical parameter mean, in what way is it measured? We will answer these and other questions in the article.

Physical quantity

Let's consider what temperature is from the point of view of an isolated system in thermodynamic equilibrium. The term comes from the Latin language and means "proper mixing", "normal state", "proportionality". This value characterizes the state of thermodynamic equilibrium of any macroscopic system. In the case when it is out of equilibrium, over time there is a transition of energy from more heated objects to less heated ones. The result is an equalization (change) of temperature throughout the system. This is the first postulate (zero principle) of thermodynamics.

Temperature determines the distribution of the constituent particles of the system by energy levels and velocities, the degree of ionization of substances, the properties of equilibrium electromagnetic radiation of bodies, and the total volumetric density of radiation. Since for a system that is in thermodynamic equilibrium, the listed parameters are equal, they are usually called the temperature of the system.

Plasma

In addition to equilibrium bodies, there are systems in which the state is characterized by several temperature values ​​that are not equal to each other. Plasma is a good example. It consists of electrons (light charged particles) and ions (heavy charged particles). When they collide, energy is rapidly transferred from electron to electron and from ion to ion. But between heterogeneous elements there is a slow transition. The plasma can be in a state in which the electrons and ions individually are close to equilibrium. In this case, separate temperatures for each kind of particles can be taken. However, these parameters will differ from each other.

magnets

In bodies in which particles have a magnetic moment, energy transfer usually occurs slowly: from translational to magnetic degrees of freedom, which are associated with the possibility of changing the directions of the moment. It turns out that there are states in which the body is characterized by a temperature that does not coincide with the kinetic parameter. It corresponds to the translational motion of elementary particles. Magnetic temperature determines part of the internal energy. It can be both positive and negative. During the alignment process, energy will be transferred from particles with a higher value to particles with a lower temperature value if they are both positive or negative. Otherwise, this process will proceed in the opposite direction - the negative temperature will be "higher" than the positive one.

And why is it necessary?

The paradox lies in the fact that the layman, in order to carry out the measurement process both in everyday life and in industry, does not even need to know what temperature is. It will be sufficient for him to understand that this is the degree of heating of an object or environment, especially since we have been familiar with these terms since childhood. Indeed, most of the practical devices designed to measure this parameter actually measure other properties of substances that change with the level of heating or cooling. For example, pressure, electrical resistance, volume, etc. Further, such readings are manually or automatically converted to the desired value.

It turns out that to determine the temperature, there is no need to study physics. Most of the population of our planet lives by this principle. If the TV is working, then there is no need to understand the transient processes of semiconductor devices, to study, in the outlet or how it enters the signal. People are used to the fact that in every field there are specialists who can fix or debug the system. The layman does not want to strain his brain, because it is much better to watch a soap opera or football on the "box" while sipping cold beer.

And I want to know

But there are people, most often students, who, either to the extent of their curiosity or out of necessity, are forced to study physics and determine what temperature really is. As a result, in their search they fall into the wilds of thermodynamics and study its zero, first and second laws. In addition, an inquisitive mind will have to comprehend entropy. And at the end of his journey, he will surely admit that the definition of temperature as a parameter of a reversible thermal system, which does not depend on the type of working substance, will not add clarity to the feeling of this concept. And all the same, the visible part will be some degrees accepted by the international system of units (SI).

Temperature as kinetic energy

More "tangible" is the approach that is called the molecular-kinetic theory. It forms the idea that heat is considered as one of the forms of energy. For example, the kinetic energy of molecules and atoms, a parameter averaged over a huge number of randomly moving particles, turns out to be a measure of what is commonly called the temperature of a body. Thus, the particles of a heated system move faster than a cold one.

Since the term under consideration is closely related to the averaged kinetic energy of a group of particles, it would be quite natural to use the joule as a temperature unit. Nevertheless, this does not happen, which is explained by the fact that the energy of the thermal motion of elementary particles is very small in relation to the joule. Therefore, its use is inconvenient. Thermal motion is measured in units derived from joules by means of a special conversion factor.

Temperature units

Today, three main units are used to display this parameter. In our country, the temperature is usually measured in degrees Celsius. This unit of measure is based on the solidification point of water - an absolute value. She is the starting point. That is, the temperature of the water at which ice begins to form is zero. In this case, water serves as an exemplary measure. This convention has been adopted for convenience. The second absolute value is the steam temperature, that is, the moment when water changes from a liquid state to a gaseous state.

The next unit is degrees Kelvin. The reference point of this system is considered to be a point. Thus, one degree Kelvin is equal to one. The difference is only the reference point. We get that zero in Kelvin will be equal to minus 273.16 degrees Celsius. In 1954, at the General Conference on Weights and Measures, it was decided to replace the term "degree Kelvin" for the unit of temperature with "kelvin".

The third commonly used unit of measure is degrees Fahrenheit. Until 1960, they were widely used in all English-speaking countries. However, today in everyday life in the United States use this unit. The system is fundamentally different from those described above. The freezing point of a mixture of salt, ammonia and water in a ratio of 1:1:1 was taken as the starting point. So, on the Fahrenheit scale, the freezing point of water is plus 32 degrees, and the boiling point is plus 212 degrees. In this system, one degree is equal to 1/180 of the difference between these temperatures. So, the range from 0 to +100 degrees Fahrenheit corresponds to the range from -18 to +38 Celsius.

Absolute zero temperature

Let's see what this parameter means. Absolute zero is the limiting temperature at which the pressure of an ideal gas vanishes at a fixed volume. This is the lowest value in nature. As Mikhailo Lomonosov predicted, "this is the greatest or last degree of cold." This implies a chemical in equal volumes of gases, subject to the same temperature and pressure, contains the same number of molecules. What follows from this? There is a minimum temperature of a gas at which its pressure or volume vanishes. This absolute value corresponds to zero Kelvin, or 273 degrees Celsius.

Some interesting facts about the solar system

The temperature on the surface of the Sun reaches 5700 kelvins, and in the center of the core - 15 million kelvins. The planets of the solar system are very different from each other in terms of the level of heating. So, the temperature of the core of our Earth is about the same as on the surface of the Sun. Jupiter is considered the hottest planet. The temperature at the center of its core is five times higher than at the surface of the Sun. But the lowest value of the parameter was recorded on the surface of the moon - it was only 30 kelvins. This value is even lower than on the surface of Pluto.

Earth Facts

1. The highest temperature recorded by a person was 4 billion degrees Celsius. This value is 250 times higher than the temperature of the core of the Sun. The record was set by the New York Brookhaven Natural Laboratory in the ion collider, which is about 4 kilometers long.

2. The temperature on our planet is also not always ideal and comfortable. For example, in the city of Verkhnoyansk in Yakutia, the temperature in winter drops to minus 45 degrees Celsius. But in the Ethiopian city of Dallol, the situation is reversed. There, the average annual temperature is plus 34 degrees.

3. The most extreme conditions under which people work are recorded in gold mines in South Africa. Miners work at a depth of three kilometers at a temperature of plus 65 degrees Celsius.

There are several different temperature units.

The most famous are the following:

Degree Celsius - used in the International System of Units (SI) along with the kelvin.

The degree Celsius is named after the Swedish scientist Anders Celsius, who in 1742 proposed a new scale for measuring temperature.

The original definition of the degree Celsius depended on the definition of standard atmospheric pressure, because both the boiling point of water and the melting point of ice depend on pressure. This is not very convenient for standardizing the unit of measurement. Therefore, after the adoption of the kelvin K as the basic unit of temperature, the definition of the degree Celsius was revised.

According to the modern definition, a degree Celsius is equal to one kelvin K, and the zero of the Celsius scale is set so that the temperature of the triple point of water is 0.01 °C. As a result, the Celsius and Kelvin scales are shifted by 273.15:

In 1665, the Dutch physicist Christian Huygens, together with the English physicist Robert Hooke, first proposed using the melting points of ice and boiling points of water as reference points for the temperature scale.

In 1742, the Swedish astronomer, geologist and meteorologist Anders Celsius (1701-1744) developed a new temperature scale based on this idea. Initially, 0° (zero) was the boiling point of water, and 100° was the freezing point of water (the melting point of ice). Later, after the death of Celsius, his contemporaries and compatriots, the botanist Carl Linnaeus and the astronomer Morten Strömer, used this scale upside down (for 0 ° they began to take the temperature of melting ice, and for 100 ° - boiling water). In this form, the scale is used to this day.

According to one account, Celsius himself turned his scale on the advice of Strömer. According to other sources, the scale was turned over by Carl Linnaeus in 1745. And according to the third, the scale was turned over by Celsius's successor Morten Strömer, and in the 18th century such a thermometer was widely used under the name "Swedish thermometer", and in Sweden itself under the name of Strömer, but the famous Swedish chemist Jöns Jakob Berzelius in his work "A Guide to Chemistry ” called the scale “Celsius” and since then the centigrade scale has been named after Anders Celsius.

Degree Fahrenheit.

It is named after the German scientist Gabriel Fahrenheit, who in 1724 proposed a scale for measuring temperature.

On the Fahrenheit scale, the melting point of ice is +32°F and the boiling point of water is +212°F (at normal atmospheric pressure). In this case, one degree Fahrenheit is equal to 1/180 of the difference between these temperatures. The range 0…+100 °F Fahrenheit roughly corresponds to the range -18…+38 °C Celsius. Zero on this scale is defined as the freezing point of a mixture of water, salt and ammonia (1:1:1), and 96 °F is taken as the normal temperature of the human body.

Kelvin (before 1968 degrees Kelvin) is a unit of thermodynamic temperature in the International System of Units (SI), one of the seven basic SI units. Proposed in 1848. 1 kelvin is equal to 1/273.16 of the thermodynamic temperature of the triple point of water. The beginning of the scale (0 K) coincides with absolute zero.

Conversion to degrees Celsius: ° С \u003d K−273.15 (the temperature of the triple point of water is 0.01 ° C).

The unit is named after the English physicist William Thomson, who was awarded the title of Lord Kelvin Larg of Ayrshire. In turn, this title comes from the River Kelvin, which flows through the territory of the university in Glasgow.

	Kelvin	Degree Celsius	Fahrenheit
Absolute zero
Boiling point of liquid nitrogen
Sublimation (transition from solid to gaseous state) of dry ice
Intersection point of Celsius and Fahrenheit scales
Ice melting point
Triple point of water
Normal human body temperature
Boiling point of water at a pressure of 1 atmosphere (101.325 kPa)

Degree Reaumur - a unit of temperature in which the freezing and boiling points of water are taken as 0 and 80 degrees, respectively. Proposed in 1730 by R. A. Réaumur. The Réaumur scale has practically fallen into disuse.

Römer degree is a currently unused unit of temperature.

The Römer temperature scale was created in 1701 by the Danish astronomer Ole Christensen Römer. She became the prototype of the Fahrenheit scale, which Roemer visited in 1708.

Zero degrees is the freezing point of salt water. The second reference point is the temperature of the human body (30 degrees according to Roemer's measurements, i.e. 42 °C). Then the freezing point of fresh water is obtained as 7.5 degrees (1/8 of the scale), and the boiling point of water is 60 degrees. Thus, the Römer scale is 60 degrees. This choice seems to be explained by the fact that Römer is primarily an astronomer, and the number 60 has been the cornerstone of astronomy since Babylonian times.

Degree Rankine - a unit of temperature in the absolute temperature scale, named after the Scottish physicist William Rankin (1820-1872). Used in English-speaking countries for engineering thermodynamic calculations.

The Rankine scale starts at absolute zero, the freezing point of water is 491.67°Ra, and the boiling point of water is 671.67°Ra. The number of degrees between the freezing and boiling points of water on the Fahrenheit and Rankine scales is the same and is equal to 180.

The relationship between Kelvin and degrees Rankine: 1 K = 1.8 °Ra, degrees Fahrenheit are converted to degrees Rankine using the formula °Ra = °F + 459.67.

Degree of Delisle is a now obsolete unit of temperature measurement. It was invented by the French astronomer Joseph Nicolas Delisle (1688-1768). The Delisle scale is similar to the Réaumur temperature scale. It was used in Russia until the 18th century.

Peter the Great invited the French astronomer Joseph Nicolas Delisle to Russia, establishing the Academy of Sciences. In 1732, Delisle created a thermometer using mercury as the working fluid. The boiling point of water was chosen as zero. For one degree, such a change in temperature was taken, which led to a decrease in the volume of mercury by one hundred-thousandth.

Thus, the melting temperature of ice was 2400 degrees. However, later such a fractional scale seemed redundant, and already in the winter of 1738, Delisle's colleague at the St. Petersburg Academy, physician Josias Weitbrecht (1702-1747), reduced the number of steps from the boiling point to the freezing point of water to 150.

The “inversion” of this scale (as well as the original version of the Celsius scale) compared to those currently accepted is usually explained by purely technical difficulties associated with the calibration of thermometers.

Delisle's scale was widely used in Russia, and his thermometers were used for about 100 years. This scale was used by many Russian academics, including Mikhail Lomonosov, who, however, "turned" it, placing zero at the freezing point, and 150 degrees at the boiling point of water.

Degree Hooke - historical unit of temperature. The Hooke scale is considered the very first temperature scale with a fixed zero.

The prototype for the scale created by Hooke was a thermometer that came to him in 1661 from Florence. In Hooke's Micrographia, published a year later, there is a description of the scale he developed. Hooke defined one degree as a change in the volume of alcohol by 1/500, that is, one degree of Hooke is equal to approximately 2.4 ° C.

In 1663, the members of the Royal Society agreed to use Hooke's thermometer as a standard and to compare the readings of other thermometers with it. The Dutch physicist Christian Huygens in 1665, together with Hooke, proposed using the temperatures of melting ice and boiling water to create a temperature scale. It was the first scale with a fixed zero and negative values.

Degree Dalton is the historical unit of temperature. It has no definite meaning (in terms of traditional temperature scales such as Kelvin, Celsius or Fahrenheit) because the Dalton scale is logarithmic.

The Dalton scale was developed by John Dalton to take measurements at high temperatures, since conventional uniform-scale thermometers gave errors due to uneven expansion of the thermometric fluid.

Zero on the Dalton scale corresponds to zero Celsius. A distinctive feature of the Dalton scale is that absolute zero in it is equal to − ∞°Da, i.e. it is an unattainable value (which is actually the case, according to the Nernst theorem).

Degree Newton is a unit of temperature that is no longer in use.

Newton's temperature scale was developed by Isaac Newton in 1701 for thermophysical research and probably became the prototype of the Celsius scale.

Newton used linseed oil as a thermometric liquid. Newton took the freezing point of fresh water as zero degrees, and he designated the temperature of the human body as 12 degrees. Thus, the boiling point of water became equal to 33 degrees.

Leiden degree - historical unit of temperature used at the beginning of the 20th century to measure cryogenic temperatures below −183 °C.

This scale originates from Leiden, where Kamerlingh Onnes' laboratory was located since 1897. In 1957, H. van Dijk and M. Dureau introduced the L55 scale.

The boiling point of standard liquid hydrogen (−253 °C), consisting of 75% orthohydrogen and 25% parahydrogen, was taken as zero degrees. The second reference point is the boiling point of liquid oxygen (−193 °C).

Planck temperature , named after the German physicist Max Planck, the unit of temperature, denoted T P , in the Planck system of units. It is one of the Planck units that represents the fundamental limit in quantum mechanics. The modern physical theory is not able to describe anything hotter due to the lack of a developed quantum theory of gravity in it. Above the Planck temperature, the energy of the particles becomes so large that the gravitational forces between them become comparable to the rest of the fundamental interactions. This is the temperature of the Universe at the first moment (Planck time) of the Big Bang, according to the current ideas of cosmology.

Characterizing the thermal state of bodies.

In the world around us, there are various phenomena associated with the heating and cooling of bodies. They are called thermal phenomena. So, when heated, cold water first becomes warm, and then hot; the metal part taken out of the flame gradually cools down, etc. The degree of heating of the body, or its thermal state, we denote by the words "warm", "cold", "hot". For a quantitative assessment of this state, it serves temperature.

Temperature is one of the macroscopic parameters of a system. In physics, bodies that are made up of a very large number of atoms or molecules are called macroscopic. The dimensions of macroscopic bodies are many times greater than the dimensions of atoms. All surrounding bodies - from a table or gas in a balloon to a grain of sand - are macroscopic bodies.

The quantities characterizing the state of macroscopic bodies without taking into account their molecular structure are called macroscopic parameters. These include volume, pressure, temperature, particle concentration, mass, density, magnetization, etc. Temperature is one of the most important macroscopic parameters of a system (gas, in particular).

Temperature is a characteristic of the thermal equilibrium of a system.

It is known that in order to determine the temperature of the medium, a thermometer should be placed in this medium and wait until the temperature of the thermometer stops changing, taking a value equal to the ambient temperature. In other words, it takes some time to establish thermal equilibrium between the medium and the thermometer.

Thermal, or thermodynamic, balance called such a state in which all macroscopic parameters remain unchanged for an arbitrarily long time. This means that the volume and pressure in the system do not change, phase transformations do not occur, and the temperature does not change.

However, microscopic processes do not stop at thermal equilibrium: the speeds of molecules change, they move, they collide.

Any macroscopic body or group of macroscopic bodies - thermodynamic system can be in different states of thermal equilibrium. In each of these states, the temperature has its own well-defined value. Other quantities may have different (but constant) values. For example, the pressure of a compressed gas in a cylinder will differ from the pressure in the room and at the temperature equilibrium of the entire system of bodies in this room.

Temperature characterizes the state of thermal equilibrium of a macroscopic system: in all parts of the system that are in a state of thermal equilibrium, the temperature has the same value (this is the only macroscopic parameter that has this property).

If two bodies have the same temperature, no heat exchange occurs between them; if different, heat exchange occurs, and heat is transferred from a more heated body to a less heated one until the temperatures are completely equalized.

Temperature measurement is based on the dependence of some physical quantity (for example, volume) on temperature. This dependence is used in the temperature scale of a thermometer, a device used to measure temperature.

The action of a thermometer is based on the thermal expansion of a substance. When heated, the column of the substance used in the thermometer (for example, mercury or alcohol) increases, and when cooled, it decreases. Thermometers used in everyday life allow you to express the temperature of a substance in degrees Celsius (°C).

A. Celsius (1701-1744) - a Swedish scientist who proposed the use of a centigrade temperature scale. In the Celsius temperature scale, zero (from the middle of the 18th century) is the temperature of melting ice, and 100 degrees is the boiling point of water at normal atmospheric pressure.

Since different liquids expand differently with increasing temperature, the temperature scales in thermometers with different liquids are different.

Therefore, in physics they use ideal gas temperature scale, based on the dependence of volume (at constant pressure) or pressure (at constant volume) of gas on temperature.

Temperature is easy!

Temperature

Temperature is a measure of the average kinetic energy of molecules.
Temperature characterizes the degree of heating of bodies.

Temperature measuring instrument - thermometer.
Operating principle thermometer:
When measuring temperature, the dependence of a change in any macroscopic parameter (volume, pressure, electrical resistance, etc.) of a substance on temperature is used.
In liquid thermometers, this is the change in volume of liquid.
When two media come into contact, energy is transferred from a more heated medium to a less heated one.
In the process of measuring the temperature of the body and the thermometer come to a state of thermal equilibrium.

Liquid thermometers

In practice, liquid thermometers are often used: mercury (in the range from -35 o C to +750 o C) and alcohol (from -80 o C to +70 o C).
They use the property of a liquid to change its volume with a change in temperature.
However, each liquid has its own characteristics of volume change (expansion) at different temperatures.
As a result of comparing, for example, the readings of mercury and alcohol thermometers, there will be an exact match only at two points (at temperatures of 0 o C and 100 o C).
These shortcomings are deprived of gas thermometers.

Gas thermometers

The first gas thermometer was created by the French physicist J. Charles.

Advantages gas thermometer:
- a linear dependence of the change in gas volume or pressure on temperature is used, which is valid for all gases
- measurement accuracy from 0.003 o C to 0.02 o C
- temperature range from -271 o C to +1027 o C.

Thermal equilibrium

When two bodies of different temperatures come into contact, internal energy is transferred from a more heated body to a less heated one, and the temperatures of both bodies are equalized.
A state of thermal equilibrium sets in, in which all macroparameters (volume, pressure, temperature) of both bodies remain unchanged in the future under unchanged external conditions.

thermal equilibrium is a state in which all macroscopic parameters remain unchanged for an arbitrarily long time.
The state of thermal equilibrium of a system of bodies is characterized by temperature: all bodies of the system that are in thermal equilibrium with each other have the same temperature.
It has been established that at thermal equilibrium, the average kinetic energies of the translational motion of the molecules of all gases are the same, i.e.

For rarefied (ideal) gases, the value

and depends only on the temperature, then

where k is Boltzmann's constant

This dependence makes it possible to introduce a new temperature scale - an absolute temperature scale that does not depend on the substance used to measure the temperature.

Absolute temperature scale

Introduced by the English physicist W. Kelvin
- no negative temperatures

Absolute temperature unit in SI: [T] = 1K (Kelvin)
The zero temperature of the absolute scale is absolute zero (0K = -273 o C), the lowest temperature in nature. At present, the lowest temperature has been reached - 0.0001K.
In magnitude, 1K is equal to 1 o C.

The relationship of the absolute scale with the Celsius scale

Remember! In the formulas, the absolute temperature is denoted by the letter "T", and the temperature on the Celsius scale by the letter "t".

After introducing the absolute temperature, we get new expressions for formulas:

Average kinetic energy of translational motion of molecules

Gas pressure - the basic equation of the MKT

Root mean square velocity of molecules

Plan:

Introduction

• 1 Thermodynamic definition
  • 1.1 History of the thermodynamic approach
• 2 Definition of temperature in statistical physics
• 3 Temperature measurement
• 4 Temperature units and scale
  • 4.1 Kelvin temperature scale
  • 4.2 Celsius scale
  • 4.3 Fahrenheit
• 5 Energy of thermal motion at absolute zero
  • 5.1 Temperature and Radiation
  • 5.2 Réaumur scale
• 6 Transitions from different scales
• 7 Comparison of temperature scales
• 8 Characteristics of phase transitions
• 9 Interesting Facts
Notes
Literature

Introduction

Temperature(from lat. temperature- proper mixing, normal state) - a scalar physical quantity that characterizes the average kinetic energy of particles of a macroscopic system that is in a state of thermodynamic equilibrium per one degree of freedom.

The measure of temperature is not the movement itself, but the randomness of this movement. The randomness of the state of a body determines its temperature state, and this idea (which was first developed by Boltzmann) that a certain thermal state of a body is not at all determined by the energy of motion, but by the randomness of this motion, is the new concept in the description of thermal phenomena that we must use. ..

(P. L. Kapitsa)

In the International System of Units (SI), thermodynamic temperature is part of seven basic units and is expressed in kelvins. The composition of the derived SI values ​​\u200b\u200bwith a special name includes the Celsius temperature, measured in degrees Celsius. In practice, degrees Celsius are often used because of the historical reference to the important characteristics of water - the melting temperature of ice (0 ° C) and the boiling point (100 ° C). This is convenient, since most climatic processes, processes in wildlife, etc. are associated with this range. A change in temperature by one degree Celsius is identical to a change in temperature by one Kelvin. Therefore, after the introduction of a new definition of Kelvin in 1967, the boiling point of water ceased to play the role of an invariable reference point and, as accurate measurements show, it is no longer equal to 100 ° C, but close to 99.975 ° C.

There are also Fahrenheit scales and some others.

1. Thermodynamic definition

The existence of an equilibrium state is called the first initial position of thermodynamics. The second initial position of thermodynamics is the statement that the equilibrium state is characterized by a certain value, which, upon thermal contact of two equilibrium systems, becomes the same for them as a result of energy exchange. This value is called temperature.

1.1. History of the thermodynamic approach

The word "temperature" arose at a time when people believed that hotter bodies contained a greater amount of a special substance - caloric than less heated ones. Therefore, temperature was perceived as the strength of a mixture of body substance and caloric. For this reason, the units of measure for the strength of alcoholic beverages and temperature are called the same - degrees.

In an equilibrium state, the temperature has the same value for all macroscopic parts of the system. If two bodies in the system have the same temperature, then there is no transfer of kinetic energy of particles (heat) between them. If there is a temperature difference, then heat passes from a body with a higher temperature to a body with a lower one, because the total entropy increases in this case.

Temperature is also associated with the subjective sensations of "warmth" and "cold" associated with whether living tissue gives off heat or receives it.

Some quantum mechanical systems can be in a state in which the entropy does not increase, but decreases with the addition of energy, which formally corresponds to a negative absolute temperature. However, such states are not “below absolute zero”, but “above infinity”, since when such a system contacts a body with a positive temperature, energy is transferred from the system to the body, and not vice versa (for more details, see Quantum thermodynamics).

The properties of temperature are studied by the branch of physics - thermodynamics. Temperature also plays an important role in many areas of science, including other branches of physics as well as chemistry and biology.

2. Determination of temperature in statistical physics

In statistical physics, the temperature is determined by the formula

,

where S is the entropy, E is the energy of the thermodynamic system. The value of T introduced in this way is the same for different bodies at thermodynamic equilibrium. When two bodies come into contact, a body with a large value of T will give energy to the other.

3. Temperature measurement

To measure the thermodynamic temperature, a certain thermodynamic parameter of a thermometric substance is selected. A change in this parameter is unambiguously associated with a change in temperature. A classic example of a thermodynamic thermometer is a gas thermometer, in which the temperature is determined by measuring the pressure of a gas in a constant volume cylinder. Absolute radiation, noise, and acoustic thermometers are also known.

Thermodynamic thermometers are very complex devices that cannot be used for practical purposes. Therefore, most measurements are made using practical thermometers, which are secondary, since they cannot directly relate some property of a substance to temperature. To obtain the interpolation function, they must be calibrated in reference points of the international temperature scale. The most accurate practical thermometer is the platinum resistance thermometer. Temperature measuring instruments are often graduated on relative scales - Celsius or Fahrenheit.

In practice, temperature is also used to measure

• liquid and mechanical thermometers,
• thermocouple
• resistance thermometer,

• gas thermometer,
• pyrometer.

The latest temperature measurement methods based on the measurement of laser radiation parameters have been developed.

4. Units and scale of temperature measurement

From the fact that temperature is the kinetic energy of molecules, it is clear that it is most natural to measure it in energy units (that is, in the SI system in joules). However, temperature measurement began long before the creation of the molecular kinetic theory, so practical scales measure temperature in conventional units - degrees.

4.1. Kelvin temperature scale

The concept of absolute temperature was introduced by W. Thomson (Kelvin), in connection with which the absolute temperature scale is called the Kelvin scale or the thermodynamic temperature scale. The unit of absolute temperature is the kelvin (K).

The absolute temperature scale is called so because the measure of the ground state of the lower temperature limit is absolute zero, that is, the lowest possible temperature at which, in principle, it is impossible to extract thermal energy from a substance.

Absolute zero is defined as 0 K, which is -273.15 °C (exactly).

The Kelvin temperature scale is a scale that is measured from absolute zero.

Of great importance is the development on the basis of the Kelvin thermodynamic scale of International practical scales based on reference points - phase transitions of pure substances, determined by methods of primary thermometry. The first international temperature scale was the ITS-27 adopted in 1927. Since 1927, the scale has been redefined several times (MTSh-48, MPTSh-68, MTSh-90): the reference temperatures and interpolation methods have changed, but the principle remains the same - the basis of the scale is a set of phase transitions of pure substances with certain values ​​of thermodynamic temperatures and interpolation instruments graduated 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.

The 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, due to which the temperature has to be expressed a negative number. For such cases, absolute temperature scales were introduced.

One of them is called the Rankin scale, and the other is called the absolute thermodynamic scale (Kelvin scale); temperatures are measured, respectively, in degrees Rankine (°Ra) and kelvins (K). Both scales start at absolute zero. They differ in that the price of one division on the Kelvin scale is equal to the division price of the Celsius scale, and the division price of the Rankine scale is equivalent to the division price of thermometers with the Fahrenheit scale. The freezing point of water at standard atmospheric pressure corresponds to 273.15 K, 0 °C, 32 °F.

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

4.2. Celsius

In engineering, medicine, meteorology and everyday life, the Celsius scale is used, in which the temperature of the triple point of water is 0.008 ° C, and, therefore, the freezing point of water at a pressure of 1 atm is 0 ° C. Currently, the Celsius scale is determined through the Kelvin scale: the price of one division in the Celsius scale is equal to the price of a division of the Kelvin scale, t (° C) = T (K) - 273.15. Thus, the boiling point of water, originally chosen by Celsius as a reference point of 100 ° C, has lost its meaning, and according to modern estimates, the boiling point of water at normal atmospheric pressure is about 99.975 ° C. The Celsius scale is practically very convenient, since water is very common on our planet and our life is based on it. Zero Celsius is a special point for meteorology, as it is associated with the freezing of atmospheric water. The scale was proposed by Anders Celsius in 1742.

4.3. Fahrenheit

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

The current definition of the Fahrenheit scale is as follows: it is a temperature scale, 1 degree (1 °F) of which is equal to 1/180 of the difference between the boiling point of water and the melting of ice at atmospheric pressure, and the melting point of ice is +32 °F. The temperature on the Fahrenheit scale is related to the temperature on the Celsius scale (t ° C) by the ratio t ° C \u003d 5/9 (t ° F - 32), t ° F \u003d 9/5 t ° C + 32. Proposed by G. Fahrenheit in 1724 .

5. Energy of thermal motion at absolute zero

As matter cools, many forms of thermal energy and their associated effects simultaneously decrease in magnitude. Matter moves from a less ordered state to a more ordered state.

... the modern concept of absolute zero is not the concept of absolute rest, on the contrary, at absolute zero there can be movement - and it is, but it is a state of complete order ...

P. L. Kapitsa (Properties of liquid helium)

The gas turns into a liquid and then crystallizes into a solid (helium remains in a liquid state at atmospheric pressure even at absolute zero). The movement of atoms and molecules slows down, their kinetic energy decreases. The resistance of most metals falls due to a decrease in the scattering of electrons by atoms of the crystal lattice vibrating with a smaller amplitude. Thus, even at absolute zero, conduction electrons move between atoms at a Fermi velocity of the order of 1×10 6 m/s.

The temperature at which the particles of matter have a minimum amount of motion, which is preserved only due to quantum mechanical motion, is the temperature of absolute zero (T = 0K).

Temperatures of absolute zero cannot be reached. The lowest temperature (450±80)×10 −12 K of the Bose-Einstein condensate of sodium atoms was obtained in 2003 by researchers from MIT. In this case, the peak of thermal radiation is in the region of wavelengths of the order of 6400 km, that is, approximately the radius of the Earth.

5.1. Temperature and Radiation

The energy emitted by a body is proportional to the fourth power of its temperature. So, at 300 K, up to 450 watts are emitted from a square meter of surface. This explains, for example, the nighttime cooling of the earth's surface below the ambient air temperature. The radiation energy of a black body is described by the Stefan-Boltzmann law

5.2. Reaumur scale

It was proposed in 1730 by R. A. Reaumur, who described the alcohol thermometer he invented.

Unit - degree Réaumur (°R), 1 °R is equal to 1/80 of the temperature interval between the reference points - the temperature of melting ice (0 °R) and boiling water (80 °R)

1°R = 1.25°C.

At present, the scale has fallen into disuse; it has been preserved for the longest time in France, in the author's homeland.

6. Transitions from different scales

7. Comparison of temperature scales

Comparison of temperature scales

Description	Kelvin	Celsius	Fahrenheit	Rankin	Delisle	newton	Réaumur	Römer
Absolute zero	0	−273.15	−459.67	0	559.725	−90.14	−218.52	−135.90
Melting point of Fahrenheit mixture (salt and ice in equal amounts)	255.37	−17.78	0	459.67	176.67	−5.87	−14.22	−1.83
Freezing point of water (Reference conditions)	273.15	0	32	491.67	150	0	0	7.5
Average human body temperature¹	310.0	36.6	98.2	557.9	94.5	12.21	29.6	26.925
Boiling point of water (Normal conditions)	373.15	100	212	671.67	0	33	80	60
melting titanium	1941	1668	3034	3494	−2352	550	1334	883
Sun surface	5800	5526	9980	10440	−8140	1823	4421	2909

¹ The normal average human body temperature is 36.6°C ±0.7°C, or 98.2°F ±1.3°F. The commonly given value of 98.6 °F is an exact Fahrenheit conversion of the 19th century German value of 37 °C. However, this value is not within the range of the normal average human body temperature, since the temperature of different parts of the body is different.

Some values ​​in this table have been rounded.

8. Characteristics of phase transitions

To describe the points of phase transitions of various substances, the following temperature values ​​are used:

• Melting temperature
• Boiling temperature
• Annealing temperature
• Sintering temperature
• Synthesis temperature
• Air mass temperature
• soil temperature
• homologous temperature
• triple point
• Debye temperature (Characteristic temperature)
• Curie temperature

9. Interesting facts

The lowest temperature on Earth before 1910 −68, Verkhoyansk

• The highest temperature created by man, ~ 10 trillion. K (which is comparable to the temperature of the Universe in the first seconds of its life) was reached in 2010 during the collision of lead ions accelerated to near-light speeds. The experiment was carried out at the Large Hadron Collider
• The highest theoretically possible temperature is the Planck temperature. A higher temperature cannot exist, since everything turns into energy (all subatomic particles will collapse). This temperature is approximately equal to 1.41679(11)×10 32 K (approximately 142 nonillion K).
• The lowest temperature created by man was obtained in 1995 by Eric Cornell and Carl Wiman from the USA by cooling rubidium atoms. . It was above absolute zero by less than 1/170 billion fraction of K (5.9×10 −12 K).
• The surface of the Sun has temperatures around 6000 K.
• Seeds of higher plants remain viable after cooling to -269 °C.

Notes

1. GOST 8.417-2002. UNITS OF VALUES - nolik.ru/systems/gost.htm
2. The concept of temperature - temperatures.ru/mtsh/mtsh.php?page=1
3. I. P. Bazarov. Thermodynamics, M., Higher School, 1976, p. 13-14.
4. Platinum - temperatures.ru/mtsh/mtsh.php?page=81 resistance thermometer - the main device MTSh-90.
5. Laser thermometry - temperatures.ru/newmet/newmet.php?page=0
6. Fixed points MTSh-90 - temperatures.ru/mtsh/mtsh.php?page=3
7. Development of a new definition of kelvin - temperatures.ru/kelvin/kelvin.php?page=2
8. D. A. Parshin, G. G. Zegrya Critical point. Properties of a substance in a critical state. Triple point. Phase transitions of the second kind. Methods for obtaining low temperatures. - edu.ioffe.spb.ru/edu/thermodinamics/lect11h.pdf . Statistical thermodynamics. Lecture 11. St. Petersburg Academic University.
9. About various body temperature measurements - hypertextbook.com/facts/LenaWong.shtml
10. BBC News - Large Hadron Collider (LHC) generates a "mini-Big Bang" - www.bbc.co.uk/news/science-environment-11711228
11. Everything about everything. Temperature records - tem-6.narod.ru/weather_record.html
12. The wonders of science - www.seti.ee/ff/34gin.swf

Literature

• B. I. Spassky History of physics Ch.I - osnovanija.narod.ru/History/Spas/T1_1.djvu. - Moscow: "Higher School", 1977.
• Sivukhin D.V. Thermodynamics and molecular physics. - Moscow: "Science", 1990.

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