The concept of temperature and temperature scale. Temperature

TEMPERATURE AND ITS MEASUREMENT.

EXPERIMENTAL GAS LAWS.

1. Thermal equilibrium. Temperature.

Temperature is a physical quantity characterizing the degree of heating of a body. If two bodies of different temperatures are brought into contact, then, as experience shows, the more heated body will cool, and the less heated one will heat up, i.e. is happening heat exchange– transfer of energy from a more heated body to a less heated one without doing work.

The energy transferred during heat exchange is called amount of heat.

Some time after the bodies are brought into contact, they acquire the same degree of heating, i.e. come into a state thermal equilibrium.

Thermal equilibrium- this is a state of a system of bodies in thermal contact in which heat exchange does not occur and all macroparameters of the bodies remain unchanged if external conditions do not change.

In this case, two parameters - volume and pressure - can be different for different bodies of the system, and the third, temperature, in the case of thermal equilibrium is the same for all bodies of the system. The determination of temperature is based on this.

A physical parameter that is the same for all bodies of the system that are in a state of thermal equilibrium is called temperature this system.

For example, the system consists of two vessels with gas. Let's bring them into contact. The volume and pressure of the gas in them can be different, but the temperature as a result of heat exchange will become the same.

2.Temperature measurement.

To measure temperature, physical instruments are used - thermometers, in which the temperature value is judged by a change in any parameter.

To create a thermometer you need:

Select a thermometric substance whose parameters (characteristics) change with temperature changes (for example, mercury, alcohol, etc.);

Select a thermometric value, i.e. a value that changes with temperature (for example, the height of the mercury or alcohol column, the value of electrical resistance, etc.);

Calibrate the thermometer, i.e. create a scale on which the temperature will be measured. To do this, the thermometric body is brought into thermal contact with bodies whose temperatures are constant. For example, when constructing the Celsius scale, the temperature of a mixture of water and ice in a state of melting is taken to be 0 0 C, and the temperature of a mixture of water vapor and water in a state of boiling at a pressure of 1 atm. – for 100 0 C. The position of the liquid column is noted in both cases, and then the distance between the resulting marks is divided into 100 divisions.

When measuring temperature, the thermometer is brought into thermal contact with the body whose temperature is being measured, and after thermal equilibrium is established (the thermometer readings stop changing), the thermometer reading is read.

3. Experimental gas laws.

The parameters describing the state of the system are interdependent. It is difficult to establish the dependence of three parameters on each other at once, so let’s simplify the task a little. Let us consider the processes in which

a) the amount of substance (or mass) is constant, i.e. ν=const (m=const);

b) the value of one of the parameters is fixed, i.e. Constantly either pressure, or volume, or temperature.

Such processes are called isoprocesses.

1).Isothermal process those. a process that occurs with the same amount of substance at a constant temperature.

Explored by Boyle (1662) and Marriott (1676).

The simplified experimental scheme is as follows. Let's consider a vessel with gas, closed with a movable piston, on which weights are installed to balance the gas pressure.

Experience has shown that the product of pressure and the volume of a gas at a constant temperature is a constant value. This means

PV= const

Boyle-Mariotte Law.

The volume V of a given amount of gas ν at a constant temperature t 0 is inversely proportional to its pressure, i.e. . .

Graphs of isothermal processes.

A graph of pressure versus volume at constant temperature is called an isotherm. The higher the temperature, the higher the isotherm appears on the graph.

2).Isobaric process those. a process that occurs with the same amount of substance at constant pressure.

Explored by Gay-Lussac (1802).

The simplified diagram is as follows. The container with gas is closed by a movable piston on which a weight is installed that balances the gas pressure. The container with gas heats up.

Experience has shown that when a gas is heated at constant pressure, its volume changes according to the following law: where V 0 is the volume of gas at temperature t 0 = 0 0 C; V is the volume of gas at temperature t 0, α v is the temperature coefficient of volumetric expansion,

Gay-Lussac's Law.

The volume of a given amount of gas at constant pressure depends linearly on temperature.

Graphs of isobaric processes.

A graph of the volume of a gas versus temperature at constant pressure is called an isobar.

If we extrapolate (continue) the isobars to the region of low temperatures, then they will all converge at the point corresponding to the temperature t 0 = - 273 0 C.

3).Isochoric process, i.e. a process that occurs with the same amount of substance at a constant volume.

Explored by Charles (1802).

The simplified diagram is as follows. The container with gas is closed by a movable piston, on which weights are installed to balance the gas pressure. The vessel heats up.

Experience has shown that when a gas is heated at a constant volume, its pressure changes according to the following law: where P 0 is the volume of gas at temperature t 0 = 0 0 C; P – volume of gas at temperature t 0 , α p – temperature coefficient of pressure,

Charles's Law.

The pressure of a given amount of gas at constant volume depends linearly on temperature.

A graph of gas pressure versus temperature at constant volume is called an isochore.

If we extrapolate (continue) the isochores to the region of low temperatures, then they will all converge at the point corresponding to the temperature t 0 = - 273 0 C.

4. Absolute thermodynamic scale.

The English scientist Kelvin proposed moving the beginning of the temperature scale to the left to 273 0 and calling this point absolute zero temperature. The scale of the new scale is the same as the Celsius scale. The new scale is called the Kelvin scale or absolute thermodynamic scale. The unit of measurement is kelvin.

Zero degrees Celsius corresponds to 273 K. Temperature on the Kelvin scale is designated by the letter T.

T = t 0 C + 273

t 0 C = T – 273

The new scale turned out to be more convenient for recording gas laws.

Thermodynamic definition

History of the thermodynamic approach

The word “temperature” arose in those days when people believed that more heated bodies contained a larger amount of a special substance - caloric, than less heated ones. Therefore, temperature was perceived as the strength of a mixture of body matter and caloric. For this reason, the units of measurement for the strength of alcoholic beverages and temperature are called the same - degrees.

Determination of temperature in statistical physics

Temperature measuring instruments are often calibrated on relative scales - Celsius or Fahrenheit.

In practice, temperature is also measured

The most accurate practical thermometer is the platinum resistance thermometer. The latest methods for measuring temperature have been developed, based on measuring the parameters of laser radiation.

Temperature units and scale

Since 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.

Absolute temperature. Kelvin temperature scale

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

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

Absolute zero is defined as 0 K, which is equal to −273.15 °C.

The Kelvin temperature scale is a scale that starts at absolute zero.

Of great importance is the development, based on the Kelvin thermodynamic scale, of International practical scales based on reference points - phase transitions of pure substances determined by primary thermometry methods. The first international temperature scale was adopted in 1927 by ITS-27. Since 1927, the scale has been redefined several times (MTSh-48, MPTS-68, MTSh-90): 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 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 has to be expressed negative number. For such cases, absolute temperature scales were introduced.

One of them is called the Rankine scale, and the other is called the absolute thermodynamic scale (Kelvin scale); their temperatures are measured in degrees Rankine (°Ra) and kelvins (K), respectively. Both scales begin at absolute zero temperature. They differ in that the price of one division on the Kelvin scale is equal to the price of a division on the Celsius scale, and the price of one division on the Rankine scale is equivalent to the price of division 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 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. .

Celsius

In technology, medicine, meteorology and in everyday life, the Celsius scale is used, in which the temperature of the triple point of water is 0.008 °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 on the Celsius scale is equal to the price of a division on 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 significance, and modern estimates put the boiling point of water at normal atmospheric pressure at about 99.975 °C. The Celsius scale is practically very convenient, since water is very widespread 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

In England and especially in the USA, the Fahrenheit scale is used. Zero degrees Celsius is 32 degrees Fahrenheit, and 100 degrees Celsius is 212 degrees Fahrenheit.

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

Reaumur scale

Transitions from different scales

Comparison of temperature scales

Description	Kelvin	Celsius	Fahrenheit	Rankin	Delisle	Newton	Reaumur	Roemer
Absolute zero	0	−273,15	−459,67	0	559,725	−90,14	−218,52	−135,90
Melting temperature of Fahrenheit mixture (salt and ice in equal quantities)	255,37	−17,78	0	459,67	176,67	−5,87	−14,22	−1,83
Freezing point of water (Normal 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
Surface of the Sun	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 quoted value of 98.6°F is an exact conversion to Fahrenheit of the 19th century German value of 37°C. However, this value is not within the range of normal average human body temperature, since the temperature of different parts of the body is different.

Some values in this table are rounded.

Characteristics of phase transitions

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

Annealing temperature
Sintering temperature
Synthesis temperature
Air temperature
Soil temperature
Homologous temperature
Debye temperature (Characteristic temperature)

Notes

Literature

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

Physical quantity

Let's look at what temperature is from the point of view of an isolated system in thermodynamic equilibrium. The term comes from Latin and means “proper mixture”, “normal state”, “proportionality”. This quantity 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 equalization (change) of temperature throughout the system. This is the first postulate (zero law) of thermodynamics.

Temperature determines the distribution of the constituent particles of the system by energy levels and speeds, the degree of ionization of substances, the properties of equilibrium electromagnetic radiation of bodies, and the total volumetric radiation density. 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. A good example is plasma. It consists of electrons (light charged particles) and ions (heavy charged particles). When they collide, a rapid transfer of energy occurs from electron to electron and from ion to ion. But between heterogeneous elements there is a slow transition. Plasma can be in a state in which electrons and ions individually are close to equilibrium. In this case, it is possible to assume separate temperatures for each type of particle. 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 forward motion of elementary particles. Magnetic temperature determines part of the internal energy. It can be both positive and negative. During the equalization process, energy will be transferred from particles with a higher temperature to particles with a lower temperature if they are both positive or negative. In the opposite situation, this process will proceed in the opposite direction - the negative temperature will be “higher” than the positive one.

Why is this necessary?

The paradox is that the average person, 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 enough 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 practical instruments designed to measure this parameter actually measure other properties of substances that change depending on the level of heating or cooling. For example, pressure, electrical resistance, volume, etc. Further, such readings are manually or automatically recalculated to the required 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, study the socket or how the signal is received. People are accustomed to the fact that in every area there are specialists who can repair or debug the system. The average person does not want to strain his brain, because it is much better to watch a soap opera or football on the “box” while sipping a cold beer.

And I want to know

But there are people, most often these are students, who, either out of curiosity or out of necessity, are forced to study physics and determine what temperature really is. As a result, in their search they find themselves in the jungle of thermodynamics and study its zeroth, first and second laws. In addition, an inquisitive mind will have to comprehend entropy. And at the end of his journey, he will probably admit that defining 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 sense 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

A more “tangible” approach is called the molecular kinetic theory. From it, the idea is formed that heat is considered as a form of energy. For example, the kinetic energy of molecules and atoms, a parameter averaged over a huge number of chaotically moving particles, turns out to be a measure of what is commonly called the temperature of a body. Thus, particles in a heated system move faster than in a cold system.

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

Temperature units

Today, three main units are used to display this parameter. In our country, temperature is usually determined in degrees Celsius. This unit of measurement is based on the solidification point of water - the absolute value. It 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 yardstick. This convention has been adopted for convenience. The second absolute value is the vapor temperature, that is, the moment when water changes from a liquid state to a gaseous state.

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

The third commonly accepted unit of measurement is degrees Fahrenheit. Until 1960, they were widely used in all English-speaking countries. However, this unit is still used in everyday life in the United States. The system is fundamentally different from those described above. The freezing point of a mixture of salt, ammonia and water in a 1:1:1 ratio is 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. Thus, the range from 0 to +100 degrees Fahrenheit corresponds to the range from -18 to +38 Celsius.

Absolute zero temperature

Let's figure out what this parameter means. Absolute zero is the value of the limiting temperature at which the pressure of an ideal gas becomes zero for a fixed volume. This is the lowest value in nature. As Mikhailo Lomonosov predicted, “this is the greatest or last degree of cold.” From this it follows that equal volumes of gases, subject to the same temperature and pressure, contain the same number of molecules. What follows from this? There is a minimum temperature of a gas at which its pressure or volume goes to zero. 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 Kelvin, and in the center of the core - 15 million Kelvin. The planets of the solar system differ greatly from each other in terms of heating levels. Thus, the temperature of the core of our Earth is approximately 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 Kelvin. This value is even lower than on the surface of Pluto.

Facts about Earth

1. The highest temperature recorded by man was 4 billion degrees Celsius. This value is 250 times higher than the temperature of the Sun's core. The record was set by New York's Brookhaven Natural Laboratory in an 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 the opposite. 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.

Plan:

1 Thermodynamic definition
- 1.1 History of the thermodynamic approach
2 Determination 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 Reaumur scale
6 Transitions from different scales
7 Comparison of temperature scales
8 Characteristics of phase transitions
9 Interesting Facts

Introduction

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

The measure of temperature is not the movement itself, but the chaotic nature 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 temperature state of a body is not at all determined by the energy of movement, but by the randomness of this movement, is the new concept in the description of temperature phenomena that we must use. ..

(P. L. Kapitsa)

In the International System of Units (SI), thermodynamic temperature is one of the seven basic units and is expressed in kelvins. The derived SI quantities, which have a special name, include Celsius temperature, measured in degrees Celsius. In practice, degrees Celsius are often used due to their historical connection to important characteristics of water - the melting point of ice (0 °C) and the boiling point (100 °C). This is convenient since most climate processes, processes in wildlife, etc. are associated with this range. A change in temperature of one degree Celsius is equivalent to a change in temperature of 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 a constant 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 quantity, which, upon thermal contact of two equilibrium systems, becomes the same for them as a result of the exchange of energy. This quantity is called temperature.

1.1. History of the thermodynamic approach

The word “temperature” arose in those days when people believed that more heated bodies contained a larger amount of a special substance - caloric - than less heated ones. Therefore, temperature was perceived as the strength of a mixture of body matter and caloric. For this reason, the units of measurement 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 a 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 moves from a body with a higher temperature to a body with a lower one, because the total entropy increases.

Temperature is also associated with the subjective sensations of “warm” and “cold”, related to whether living tissue gives off or receives heat.

Some quantum mechanical systems may be in a state in which 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 comes into contact with 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, temperature is determined by the formula

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

3. Temperature measurement

To measure thermodynamic temperature, a certain thermodynamic parameter of the thermometric substance is selected. A change in this parameter is clearly 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 gas pressure in a cylinder of constant volume. Absolute radiation, noise, and acoustic thermometers are also known.

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

In practice, temperature is also measured

liquid and mechanical thermometers,
thermocouple,
resistance thermometer,

gas thermometer,
pyrometer.

The latest methods for measuring temperature have been developed, based on measuring the parameters of laser radiation.

4. Units and scale of temperature measurement

4.1. Kelvin temperature scale

The absolute temperature scale is so called because the measure of the ground state of the lower limit of temperature 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 equal to −273.15 °C (exactly).

The Kelvin temperature scale is a scale that starts at absolute zero.

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 (°Ra) and kelvins (K), respectively. Both scales begin at absolute zero temperature. They differ in that the price of one division on the Kelvin scale is equal to the price of a division on the Celsius scale, and the price of one division on the Rankine scale is equivalent to the price of division of thermometers with the Fahrenheit scale. The freezing point of water at standard atmospheric pressure corresponds to 273.15 K, 0 °C, 32 °F.

4.2. Celsius

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.

5. Energy of thermal motion at absolute zero

When 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 one.

... 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 exists, 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, even at absolute zero, remains in a liquid state at atmospheric pressure). The movement of atoms and molecules slows down, their kinetic energy decreases. The resistance of most metals decreases due to a decrease in electron scattering on atoms of the crystal lattice vibrating with a lower amplitude. Thus, even at absolute zero, conduction electrons move between atoms with a Fermi speed of the order of 1 × 10 6 m/s.

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

Absolute zero temperature 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 located in the wavelength region 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 cooling of the earth's surface at night below the ambient temperature. The radiation energy of an absolutely black body is described by the Stefan-Boltzmann law

5.2. Reaumur scale

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

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

1 °R = 1.25 °C.

Currently, the scale has fallen out of use; it survived longest in France, 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	Reaumur	Roemer
Absolute zero	0	−273.15	−459.67	0	559.725	−90.14	−218.52	−135.90
Melting temperature of Fahrenheit mixture (salt and ice in equal quantities)	255.37	−17.78	0	459.67	176.67	−5.87	−14.22	−1.83
Freezing point of water (Normal 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
Surface of the Sun	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 quoted value of 98.6 °F is an exact conversion to Fahrenheit of the 19th century German value of 37 °C. However, this value is not within the range of 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 phase transition points of various substances, the following temperature values are used:

Melting temperature
Boiling temperature
Annealing temperature
Sintering temperature
Synthesis temperature
Air temperature
Soil temperature
Homologous temperature
Triple point
Debye temperature (Characteristic temperature)
Curie temperature

9. Interesting facts

The lowest temperature on Earth until 1910 −68, Verkhoyansk

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 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 Wieman from the USA by cooling rubidium atoms. . It was above absolute zero by less than 1/170 billionth of a fraction of a K (5.9 × 10 −12 K).
The surface of the Sun has temperatures of about 6000 K.
Seeds of higher plants remain viable after cooling to −269 °C.

Notes

GOST 8.417-2002. UNITS OF QUANTITIES - nolik.ru/systems/gost.htm
The concept of temperature - temperatures.ru/mtsh/mtsh.php?page=1
I. P. Bazarov. Thermodynamics, M., Higher School, 1976, p. 13-14.
Platinum - temperatures.ru/mtsh/mtsh.php?page=81 resistance thermometer - the main device MTSH-90.
Laser thermometry - temperatures.ru/newmet/newmet.php?page=0
MTSH-90 reference points - temperatures.ru/mtsh/mtsh.php?page=3
Development of a new definition of Kelvin - temperatures.ru/kelvin/kelvin.php?page=2
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.
About various body temperature measurements - hypertextbook.com/facts/LenaWong.shtml (English)
BBC News - Large Hadron Collider (LHC) generates a "mini-Big Bang" - www.bbc.co.uk/news/science-environment-11711228
Everything about everything. Temperature records - tem-6.narod.ru/weather_record.html
Wonders of science - www.seti.ee/ff/34gin.swf

Literature

B. I. Spassky History of physics Part 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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This abstract is based on an article from Russian Wikipedia. Synchronization completed 07/09/11 16:20:43
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In school and university textbooks you can find many different explanations of temperature. Temperature is defined as a value that distinguishes hot from cold, as the degree of heating of a body, as a characteristic of the state of thermal equilibrium, as a value proportional to the energy per degree of freedom of a particle, etc. and so on. Most often, the temperature of a substance is defined as a measure of the average energy of thermal motion of particles of a substance, or as a measure of the intensity of thermal motion of particles. The celestial being of physics, the theorist, will be surprised: “What is incomprehensible here? Temperature is dQ/ dS, Where Q- warmth, and S- entropy! Such an abundance of definitions raises the suspicion among any critically thinking person that a generally accepted scientific definition of temperature does not currently exist in physics.

Let's try to find a simple and specific interpretation of this concept at a level accessible to a high school graduate. Let's imagine this picture. The first snow fell, and two brothers started a fun game known as “snowballs” during recess at school. Let's see what energy is transferred to the players during this competition. For simplicity, we assume that all projectiles hit the target. The game is going on with a clear advantage for the older brother. He also has larger snow balls, and he throws them at greater speed. The energy of all the snowballs thrown by him, where N With– number of throws, and - average kinetic energy of one ball. The average energy is found using the usual formula:

Here m- mass of snowballs, and v- their speed.

However, not all the energy expended by the older brother will be transferred to his younger partner. In fact, snowballs hit the target at different angles, so some of them, when reflected from a person, carry away part of the original energy. True, there are also “successfully” thrown balls, which can result in a black eye. In the latter case, all the kinetic energy of the projectile is transferred to the subject being fired upon. Thus, we come to the conclusion that the energy of the snowballs transferred to the younger brother will be equal to E With, A
, Where Θ With– the average value of kinetic energy that is transferred to the younger partner when one snow ball hits him. It is clear that the greater the average energy per thrown ball, the greater the average energy will be Θ With, transmitted to the target by one projectile. In the simplest case, the relationship between them can be directly proportional: Θ With =a. Accordingly, the junior student spent energy during the entire competition
, but the energy transferred to the older brother will be less: it is equal
, Where N m– number of throws, and Θ m– the average energy of one snowball absorbed by its older brother.

Something similar happens during the thermal interaction of bodies. If you bring two bodies into contact, the molecules of the first body will transfer energy to the second body in the form of heat in a short period of time.
, Where Δ S 1 is the number of collisions of molecules of the first body with the second body, and Θ 1 is the average energy that a molecule of the first body transfers to the second body in one collision. During the same time, the molecules of the second body will lose energy
. Here Δ S 2 is the number of elementary acts of interaction (number of impacts) of molecules of the second body with the first body, and Θ 2 - the average energy that a molecule of the second body transfers in one blow to the first body. Magnitude Θ in physics it is called temperature. As experience shows, it is related to the average kinetic energy of the molecules of bodies by the ratio:

(2)

And now we can summarize all the above arguments. What conclusion should we draw regarding the physical content of the quantity Θ ? It is, in our opinion, completely obvious.

body transfers to another macroscopic object in one

collision with this object.

As follows from formula (2), temperature is an energy parameter, which means that the unit of temperature in the SI system is the joule. So, strictly speaking, you should complain something like this: “It seems like I caught a cold yesterday, my head hurts, and my temperature is as much as 4.294·10 -21 J!” Isn't it an unusual unit for measuring temperature, and the value is somehow too small? But don't forget that we are talking about energy that is a fraction of the average kinetic energy of just one molecule!

In practice, temperature is measured in arbitrarily chosen units: florents, kelvins, degrees Celsius, degrees Rankine, degrees Fahrenheit, etc. (I can determine the length not in meters, but in cables, fathoms, steps, vershoks, feet, etc. I remember that in one of the cartoons the length of a boa constrictor was calculated even in parrots!)

To measure temperature, it is necessary to use some sensor, which should be brought into contact with the object under study. We will call this sensor thermometric body . A thermometric body must have two properties. Firstly, it must be significantly smaller than the object under study (more correctly, the heat capacity of the thermometric body should be much less than the heat capacity of the object under study). Have you ever tried to measure the temperature of, say, a mosquito using a regular medical thermometer? Try it! What, nothing works out? The thing is that during the process of heat exchange, the insect will not be able to change the energy state of the thermometer, since the total energy of the mosquito molecules is negligible compared to the energy of the thermometer molecules.

Well, okay, I’ll take a small object, for example, a pencil, and with its help I’ll try to measure my temperature. Again, something is not going well... And the reason for the failure is that the thermometric body must have one more mandatory property: upon contact with the object under study, changes must occur in the thermometric body that can be recorded visually or using instruments.

Take a closer look at how a regular household thermometer works. Its thermometric body is a small spherical vessel connected to a thin tube (capillary). The vessel is filled with liquid (most often mercury or colored alcohol). Upon contact with a hot or cold object, the liquid changes its volume, and the height of the column in the capillary changes accordingly. But in order to register changes in the height of a liquid column, it is also necessary to attach a scale to the thermometric body. A device containing a thermometric body and a scale chosen in a certain way is called thermometer . The most widely used thermometers at present are the Celsius scale and the Kelvin scale.

The Celsius scale is established by two reference (reference) points. The first reference point is the triple point of water - those physical conditions under which the three phases of water (liquid, gas, solid) are in equilibrium. This means that the mass of liquid, the mass of water crystals and the mass of water vapor remain unchanged under these conditions. In such a system, of course, the processes of evaporation and condensation, crystallization and melting occur, but they balance each other. If very high accuracy of temperature measurement is not needed (for example, in the manufacture of household thermometers), the first reference point is obtained by placing the thermometric body in snow or ice that melts at atmospheric pressure. The second reference point is the conditions under which liquid water is in equilibrium with its vapor (in other words, the boiling point of water) at normal atmospheric pressure. Marks are made on the thermometer scale corresponding to reference points; the interval between them is divided into one hundred parts. One division of the scale chosen in this way is called a degree Celsius (˚C). The triple point of water is taken to be 0 degrees Celsius.

The Celsius scale has received the greatest practical use in the world; unfortunately, it has a number of significant drawbacks. Temperature on this scale can take negative values, while kinetic energy and, accordingly, temperature can only be positive. In addition, the readings of thermometers with the Celsius scale (with the exception of reference points) depend on the choice of thermometric body.

The Kelvin scale does not have the disadvantages of the Celsius scale. An ideal gas must be used as a working substance in thermometers with the Kelvin scale. The Kelvin scale is also established by two reference points. The first reference point is the physical conditions under which the thermal motion of ideal gas molecules stops. This point is taken as 0 on the Kelvin scale. The second reference point is the triple point of water. The interval between reference points is divided into 273.15 parts. One division of the scale chosen in this way is called kelvin (K). The number of divisions 273.15 was chosen so that the division price of the Kelvin scale coincides with the division price of the Celsius scale, then the change in temperature on the Kelvin scale coincides with the change in temperature on the Celsius scale; This makes it easier to move from reading one scale to another. Temperature on the Kelvin scale is usually indicated by the letter T. Relationship between temperatures t in Celsius scale and temperature T, measured in kelvins, is established by the relations

And
.

To change from temperature T, measured in K, to temperature Θ Boltzmann's constant is used in joules k=1.38·10 -23 J/K, it shows how many joules per 1 K:

Θ = kT.

Some clever people try to find some secret meaning in the Boltzmann constant; meanwhile k- the most ordinary coefficient for converting temperature from Kelvin to Joules.

Let us draw the reader's attention to three specific features of temperature. Firstly, it is an averaged (statistical) parameter of an ensemble of particles. Imagine that you decided to find the average age of people on Earth. To do this, we go to the kindergarten, sum up the ages of all the children and divide this amount by the number of children. It turns out that the average age of people on Earth is 3.5 years! It seemed like they thought it right, but the result they got was ridiculous. But the whole point is that in statistics you need to operate with a huge number of objects or events. The higher their number (ideally it should be infinitely large), the more accurate the value of the average statistical parameter will be. Therefore, the concept of temperature is applicable only to bodies containing a huge number of particles. When a journalist, in pursuit of a sensation, reports that the temperature of particles falling on a spaceship is several million degrees, the relatives of the astronauts do not have to faint: nothing terrible happens to the ship: just an illiterate writer passes off the energy of a small number of cosmic particles as temperature. But if the ship, heading to Mars, were to lose its course and approach the Sun, then there would be trouble: the number of particles bombarding the ship is enormous, and the temperature of the solar corona is 1.5 million degrees.

Secondly, temperature characterizes thermal, i.e. disordered movement of particles. In an electronic oscilloscope, the picture on the screen is drawn by a narrow stream of electrons, focused to a point. These electrons pass through a certain identical potential difference and acquire approximately the same speed. For such an ensemble of particles, a competent specialist indicates their kinetic energy (for example, 1500 electron volts), which, of course, is not the temperature of these particles.

Finally, thirdly, we note that the transfer of heat from one body to another can be carried out not only due to the direct collision of particles of these bodies, but also due to the absorption of energy in the form of quanta of electromagnetic radiation (this process occurs when you sunbathe on the beach) . Therefore, a more general and accurate definition of temperature should be formulated as follows:

The temperature of a body (substance, system) is a physical quantity that is numerically equal to the average energy that a molecule of this

body transfers to another macroscopic object in one

the elementary act of interaction with this object.

In conclusion, let's return to the definitions discussed at the beginning of this article. From formula (2) it follows that if the temperature of the substance is known, then the average energy of the particles of the substance can be unambiguously determined. Thus, temperature is really a measure of the average energy of thermal motion of molecules or atoms (note, by the way, that the average energy of particles cannot be determined directly in experiment). On the other hand, kinetic energy is proportional to the square of the speed; This means that the higher the temperature, the higher the speed of the molecules, the more intense their movement. Therefore, temperature is a measure of the intensity of thermal motion of particles. These definitions are certainly acceptable, but they are too general and purely qualitative in nature.

Space as a premonition We are talking about the flight unit where he served, and where the very plane on which German Titov flew was preserved as a monument

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