TEMPERATURE AND ITS MEASUREMENT.
EXPERIMENTAL GAS LAWS.
1. Thermal equilibrium. Temperature.
Temperature- This physical quantity, characterizing the degree of heating of the 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 same degree 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 don't 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 00C, and the temperature of a mixture of water vapor and water in a state of boiling at a pressure of 1 atm. - for 1000C. 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 t0 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 t0 = 00C; V is the volume of gas at temperature t0, 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 t0 = - 2730C.
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 t0 = 00C; P – volume of gas at temperature t0, 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 t0 = - 2730C.
4. Absolute thermodynamic scale.
The English scientist Kelvin proposed moving the beginning of the temperature scale to the left to 2730 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= t0 C+ 273
t0 C= T– 273
The new scale turned out to be more convenient for recording gas laws.
temperature is:
temperature TEMPERATURE-s; and.[lat. temperatura - correct ratio, normal state] 1. Quantity characterizing thermal state of some. bodies, substances. Moderate, medium t. Permanent, indoor etc. July, summer etc. Night, day, etc. T. water, air. T. melting, boiling, freezing of something. bodies. T. in the room. T. Celsius, Fahrenheit. T. below zero. Fluctuations, temperature changes. Raise or lower the temperature. Heat, bring smth. until sometime temperature. Monitor the temperature. 2. The degree of warmth of the human body as an indicator of health. Increased, normal, decreased, etc. T. wounded. Knock someone down temperature. T. increases. T. jumps (colloquial). The patient is at forty degrees. Measure the temperature with a thermometer, hand, lips. 3. Razg. Increased body warmth as an indicator of ill health. The child has He doesn't have a fever. Go to work with a fever, work with a fever. ◁ Temperature, -i; and. Will soften.(3 digits). How is your t.? Temperature, oh, oh. T-th changes. T. electric furnace mode. T curve(graph of changes in digital temperature indicators). T. seam (tech.; gap, gap between in parts. design that makes it safe for adjacent parts to expand as the temperature rises). T. leaf(a sheet containing a record of the patient’s daily temperature). * * * temperature (from Latin temperatura - proper mixing, normal state), a physical quantity characterizing the state of thermodynamic equilibrium of a system. The temperature of all parts of an isolated system in equilibrium is the same. If the system is not in equilibrium, then heat exchange occurs between its parts that have different temperatures. Those bodies that have an average temperature have a higher temperature. kinetic energy molecules (atoms) above. Temperatures are measured with thermometers based on the dependence of any property of the body (volume, electrical resistance, etc.) on temperature. Theoretically, temperature is determined on the basis of the second law of thermodynamics as the derivative of the energy of a body by its entropy. The temperature determined in this way is always positive; it is called absolute temperature or temperature on the thermodynamic temperature scale (denoted T). For a unit absolute temperature Kelvin (K) is used in SI. Temperature values on the Celsius scale ( t, °C) are related to absolute temperature by the relation t = T - 273.15 K (1°C = 1°K). * * * TEMPERATURE TEMPERATURE (from Latin temperatura - proper mixing, normal state), a physical quantity characterizing the state of thermodynamic equilibrium of a system. The temperature of all parts of an isolated system in equilibrium is the same. If the system is not in equilibrium, then heat exchange occurs between its parts that have different temperatures ( cm. HEAT EXCHANGE). Those bodies whose average kinetic energy of molecules (atoms) is higher have a higher temperature. Temperature is measured with thermometers based on the dependence of any property of the body (volume, electrical resistance, etc.) on temperature. Theoretically, temperature is determined based on the second law of thermodynamics ( cm. SECOND LAW OF THERMODYNAMICS) as a derivative of the energy of a body by its entropy. Thus, the determined temperature is always positive; it is called absolute temperature or temperature on the thermodynamic temperature scale ( cm. THERMODYNAMIC TEMPERATURE SCALE (denoted T). Per unit of absolute temperature in SI ( cm. The SI (system of units) is kelvin (K). Temperature values on the Celsius scale ( t, °C) are related to absolute temperature by the relation t=T-273.15K (1 °C=1 K).encyclopedic Dictionary. 2009.
The concept of temperature and temperature scales
Temperature measuring instruments
Lecture No. 7
Non-contact mechanism position sensors
The most common non-contact position sensors following types: inductive, generator, magnetic reed switch and photoelectronic. These sensors do not have mechanical contact with the moving object, the position of which is controlled.
Non-contact position sensors provide high speed and high frequency of activation of the mechanism. A certain disadvantage of these sensors is the dependence of their accuracy on changes in supply voltage and temperature. Depending on the requirements, the output device of these devices can be either a non-contact logical element or an electrical relay.
In precision stopping schemes for electric drives, non-contact sensors can be used both to issue a command to switch to a reduced speed, and for a final stop.
Thermocouple
Resistance thermometer
Pyrometer
Temperature is a quantity that characterizes the thermal state of a body. According to kinetic theory, temperature is defined as a measure of the kinetic energy of the translational motion of molecules. Hence, temperature is a conditional statistical quantity directly proportional to the average kinetic energy of the molecules of the body.
“... 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).
t= T-T o (7.1),
where T o =273.15 K;
t- temperature in degrees Celsius;
T - temperature in Kelvin.
Temperature expressed in degrees Celsius is denoted “°C”.
In terms of unit size of a physical quantity, the degree Celsius is equal to the Kelvin.
Temperature is measured using measuring instruments that use various thermometric properties of liquids, gases and solids. Such measuring instruments include:
Expansion thermometers;
Manometric thermometers;
Resistance thermometers with ratiometers or bridges;
Thermocouples with millivoltmeters or potentiometers;
Radiation pyrometers.
Temperature is measured by contact (using resistance thermometers, manometric thermometers and thermoelectric thermometers) and non-contact (using pyrometers) methods.
Things to remember:
The highest accuracy of temperature measurements is achieved using contact measurement methods;
The non-contact method is used for measuring high temperatures, where it is impossible to measure using contact methods and high accuracy is not required.
The temperature measuring system is a combination of a thermometric converter (sensor) and a secondary measuring device.
Thermometric transducer is a temperature measuring transducer designed to generate a signal of measurement information in a form convenient for transmission of further conversion, processing and/or storage, but not amenable to direct perception by observation.
Thermometric converters include:
Resistance thermometers;
Thermoelectric thermometers (thermocouples);
Radiation pyrometer telescope.
Table 1
| Thermometric property | Device name | Limits of long-term use, 0С | |
| Lower | Upper | ||
| Thermal expansion | Liquid glass thermometers | -190 | |
| Pressure change | Manometric thermometers | -160 | |
| Change in electrical resistance | Electrical resistance thermometers | -200 | |
| Semiconductor resistance thermometers | -90 | ||
| Thermoelectric effects | Thermoelectric thermometers (thermocouples) standardized | -50 | |
| Special thermoelectric thermometers (thermocouples) | |||
| Thermal radiation | Optical pyrometers | ||
| Radiation pyrometers | |||
| Photoelectric pyrometers | |||
| Color pyrometers |
A secondary measuring device is a measuring instrument that converts the output signal of a thermometric converter into a numerical value.
Ratiometers, bridges, millivoltmeters, and automatic potentiometers are used as secondary measuring instruments.
Methods and technical means temperature measurements
1. Expansion thermometers and pressure thermometers
Liquid glass thermometers.
The oldest devices for measuring temperature - liquid glass thermometers - use the thermometric property thermal expansion tel. The action of thermometers is based on the difference in the coefficients of thermal expansion of the thermometric substance and the shell in which it is located (thermometric glass or, less commonly, quartz).
A liquid thermometer consists of a glass bottle and a capillary tube. The thermometric substance fills the balloon and partially the capillary tube. The free space in the capillary tube is filled with an inert gas or may be under vacuum. The part of the capillary tube protruding beyond the upper division of the scale serves to protect the thermometer from damage due to excessive overheating.
Chemically pure mercury is most often used as a thermometric substance. It does not wet glass and remains liquid over a wide temperature range. In addition to mercury, other liquids, mainly of organic origin, are also used as thermometric substances in glass thermometers. For example: methyl and ethyl alcohol, kerosene, pentane, toluene, gallium, thallium amalgam.
The main advantages of glass liquid thermometers are ease of use and fairly high measurement accuracy even for mass-produced thermometers. The disadvantages of glass thermometers include: poor visibility of the scale (if you do not use special magnifying optics) and the impossibility of automatically recording readings, transmitting readings over a distance and repairing them.
Glass liquid thermometers are widely used and are available in the following main varieties:
1. technical mercury, with an embedded scale, with the lower part immersed in the measured medium, straight and angular;
2. laboratory mercury, stick or with an embedded scale, immersed in the measured medium to the measured temperature mark, straight, small outer diameter;
3. liquid thermometers (not mercury); 4. increased accuracy and exemplary mercury thermometers;
5. electric contact mercury thermometers with an embedded scale, with contacts soldered into the capillary tube for breaking (or closing) an electrical circuit with a column of mercury;
6. special thermometers, including maximum (medical and others), minimum, meteorological and other purposes.
Manometric thermometers
The operation of manometric thermometers is based on the use of the dependence of the pressure of a substance at constant volume on temperature. The closed measuring system of a manometric thermometer consists of a sensitive element that senses the temperature of the medium being measured - a metal thermal cylinder, a working element of a pressure gauge that measures the pressure in the system, and a long connecting metal capillary. When the temperature of the medium being measured changes, the pressure in the system changes, as a result of which the sensing element moves the needle or pen along the scale of the pressure gauge, graduated in degrees of temperature.
Manometric thermometers are divided into three main types:
1. liquid, in which the entire measuring system (thermocylinder, pressure gauge and connecting capillary) is filled with liquid;
2. condensation, in which the thermal cylinder is filled partly with a liquid with a low boiling point and partly with its saturated vapor, and the connecting capillary and pressure gauge are filled with saturated liquid vapor or, more often, with a special transfer fluid;
3. gas, in which the entire measuring system is filled with inert gas.
The advantages of manometric thermometers are the comparative simplicity of design and use, the possibility of remote temperature measurement and the ability to automatically record readings. The disadvantages of manometric thermometers include: relatively low measurement accuracy (accuracy class 1.6; 2.5; 4.0 and less often 1.0); short distance for remote transmission of readings (no more than 60 meters) and difficulty of repair if the measuring system is depressurized.
Manometric thermometers are not widely used in thermal power plants. In industrial heat power engineering, they are more common, especially in cases where, due to explosion or fire safety conditions, it is impossible to use electrical methods of remote temperature measurement.
2. Thermoelectric thermometers
To measure temperature in metallurgy, thermoelectric thermometers operating in the temperature range from -200 to +2500 0C and above are most widely used. This type of device is characterized by high accuracy and reliability, the ability to be used in systems for automatic control and regulation of a parameter that largely determines the progress of the technological process in metallurgical units.
The essence of the thermoelectric method is the occurrence of an emf in a conductor whose ends have different temperatures. In order to measure the resulting EMF, it is compared with the EMF of another conductor, forming a thermoelectric pair AB with the first, in the circuit of which current will flow.
The thermo-EMF of a given pair depends only on the temperature t 1 and t 2 and does not depend on the dimensions of the thermoelectrodes (length, diameter), thermal conductivity values and electrical resistivity.
To increase the sensitivity of the thermoelectric method of measuring temperature, in some cases a thermopile is used: several thermocouples connected in series, the working ends of which are at a temperature t 2, free at a known and constant temperature t 1.
Device of thermoelectric thermometers
A thermoelectric thermometer (TT) is a measuring transducer, the sensitive element of which (thermocouple) is located in a special protective fitting, which protects the thermoelectrodes from mechanical damage and exposure to the measured environment. The fittings include a protective cover and a head, inside of which there is a contact device with clamps for connecting thermoelectrodes with wires running from the measuring device to the thermometer. The thermoelectrodes along their entire length are insulated from each other and from the protective fittings by ceramic tubes.
Wire with a diameter of 0.5 mm (noble metals) and up to 3 mm (base metals) is used as thermoelectrodes. The junction at the working end of the thermocouple is formed by welding, soldering or twisting. The latter method is used for tungsten-rhenium and tungsten-molybdenum thermocouples.
Standard and non-standard thermoelectric thermometers
For measurements in metallurgy, CTs with standard calibrations are most widely used: platinum-rhodium-platinum (TPP), platinum-rhodium-platinum-rhenium (TPR), chromel-alumel (TCA), chromel-droplet (TCC), tungsten-tungsten rhenium (TVR). In some cases, CTs with non-standard calibration are also used: copper-constantan, tungsten-molybdenum (TVR), etc.
Under conditions of long-term operation at high temperatures and aggressive environments, instability of the calibration characteristic appears, which is a consequence of a number of reasons: contamination of thermoelectrode materials with impurities from protective covers, ceramic insulators and the furnace atmosphere; evaporation of one of the alloy components; mutual diffusion through the junction. The magnitude of the deviation can be significant and increases sharply with increasing temperature and duration of operation. These circumstances must be taken into account when assessing the accuracy of temperature measurements in production conditions.
Verification of technical TT
CT verification comes down to determining the temperature dependence of thermo-EMF and comparing the resulting calibration with standard values.
Graduation is carried out using two methods: by constant points or comparisons.
Calibration using constant (reference) points is the most accurate and is used for standard thermocouples. The thermocouple to be verified is placed in a crucible with high-purity metal installed in a furnace, and the area on the thermo-EMF change curve is recorded as the temperature of the metal increases or decreases. This area corresponds to the melting or crystallization temperature of the metal, and it is more preferable to calibrate according to the crystallization point. Gold, palladium, platinum, etc. are used as reference metals.
The comparison method is used to calibrate standard second-class thermocouples and technical CTs. It consists in directly measuring the thermo-EMF of a calibrated thermocouple at a constant temperature of the free ends t 0 = 0 0C and different temperatures t 2 of the working junction, the latter being determined using a standard thermometer. Thermal EMF measurements are carried out using a portable potentiometer with a measurement (reading) accuracy of no worse than 0.1 mV. The countdown is carried out after 10 minutes of exposure at this temperature.
Measuring thermo-EMF by compensation
Measuring the thermo-EMF of a thermocouple directly, by measuring the current in a constant resistance circuit, using a millivoltmeter, can be done relatively simply. However, this method has a number of disadvantages that create additional errors, which in most cases does not allow obtaining high measurement accuracy.
In measuring technology, in addition to direct measurement methods, compensation methods or methods of contrasting (comparing) an unknown quantity with a known quantity are known. Compensation methods allow for more accurate measurements, although not always as easy as direct measurements.
The main advantage of compensating thermo-EMF measurement, compared to direct measurement using a millivoltmeter, is that at the moment of measurement, the current in the thermocouple circuit is 0. This means that the value of the resistance of the external circuit does not matter: no adjustment of the resistance of the external circuit is necessary no need to worry about the influence of temperature environment there is no need for an external circuit.
Automatic potentiometers
Automatic potentiometers are used for compensation measurements of thermo-EMF without manual manipulations typical of non-automatic potentiometers. For the latter, manual manipulations after standardizing the current are reduced to the following need to move the slider motor until the galvanometer needle reaches zero. In this case, the engine moves in a very specific direction.
The measuring circuit of an automatic potentiometer is, in principle, no different from the circuit of a non-automatic potentiometer.
The circuit has three voltage sources (battery B, normal element NE and thermocouple T) and three circuits. The battery circuit is made in the form of a bridge: the BD diagonal is powered, and the CA diagonal is connected to the thermocouple circuit. The normal element circuit is connected to the CD arm of the compensation circuit. Using switch P, the electronic amplifier of the EC (including the vibration transducer) is connected to the thermocouple circuit or to the normal element circuit. When the normal element circuit is turned on, a shunt resistance R1 is introduced, parallel to the electronic amplifier, since in this case the magnitude of the unbalance voltage is much greater than when the thermocouple circuit is turned on.
Electronic automatic potentiometers are sometimes called devices with continuous balancing, since the unbalance is measured here with an alternating current frequency of 50 Hz.
3. Electrical resistance thermometers
In metallurgical practice, resistance thermometers (RT) are used to measure temperatures up to 6500C, the operating principle of which is based on the dependence of the electrical resistance of a substance on temperature. Knowing this dependence, the temperature of the medium in which it is immersed is judged by the change in the resistance value of the thermometer. The output parameter of the device is electrical quantity, which can be measured with very high accuracy (up to 0.020C), transmitted over long distances and directly used in automatic control and regulation systems.
Pure metals are used as materials for the manufacture of sensitive elements of the vehicle: platinum, copper, nickel, iron and semiconductors.
Type of function R = f(t) depends on the nature of the material and can be written as linear equation R = R 0 (1 + at), where a is the temperature coefficient of resistance, t is temperature.
The resistance of semiconductors sharply decreases with increasing temperature, i.e. they have a negative temperature coefficient of resistance almost an order of magnitude greater than that of metals. Semiconductor resistance thermometers (SRT) are mainly used to measure low temperatures.
The advantages of TSPP are small dimensions, low inertia, and high coefficient. However, they also have significant disadvantages:
1) nonlinear nature of the dependence of resistance on temperature;
2) lack of reproducibility of composition and calibration characteristics, which excludes the interchangeability of individual vehicles of this type. This leads to the release of TSPP with individual graduation.
Vehicle types and designs
To solve various problems, vehicles are divided into reference, exemplary and working, which in turn are divided into laboratory and technical.
Depending on their purpose and design, technical vehicles are divided into: submersible, surface and indoor; protected and not protected from aggressive environments; stationary and portable; thermometers of the 1st, 2nd and 3rd accuracy classes, etc. The thermometer consists of a sensitive element located in a protective steel case on which a fitting is welded. Wires reinforced with porcelain beads connect the terminals of the sensing element to a terminal block located in the head housing. The head is closed at the top with a lid, at the bottom there is a gland entry through which the installation cable is supplied. When measuring the temperature of high-pressure media, a special protective (mounting) sleeve is installed on the vehicle cover.
The sensitive element of the vehicle is made of thin metal wire with induction-free frame or frameless winding. Much less common in metallurgical practice are semiconductor resistance thermometers (SRTC) for measuring temperatures from -90 to +180 0C. They are used in thermal relays, low-temperature regulators that provide high-precision stabilization of sensitive elements of gas analyzers, chromatographs, pyrometer housings, electrodes of thermoelectric installations for express analysis of metal composition, etc.
What is temperature?
What is temperature? (definition and explanation if possible)
Sapienti sat
From lat. Temperature - normal condition
Temperature is a physical quantity that characterizes the average kinetic energy of particles of a macroscopic system in a state of thermodynamic equilibrium. In an equilibrium state, the temperature has the same value for all macroscopic parts of the system.
To measure temperature, a certain thermodynamic parameter of the thermometric substance is selected. A change in this parameter is clearly associated with a change in temperature.
Bulat 1
Temperature (from the Latin temperatura - proper mixing, normal state) is a physical quantity that approximately characterizes the average kinetic energy of particles of a macroscopic system per one degree of freedom, which is in a state of thermodynamic equilibrium. (http://ru.wikipedia.org/wiki/Temperature).
Essentially, temperature is a measure of the kinetic energy of molecules.
Ek = 3/2 * k*T, where Ek is the average kinetic energy of molecules, k is Boltzmann’s constant = 1.38 * 10^-23 J/K, T is temperature (in degrees Kelvin).
http://ru.wikipedia.org/wiki/Boltzmann_constant
In a more general thermodynamic definition: temperature is the reciprocal of the change in entropy (degree of disorder) of a system when a unit amount of heat is added to the system: 1/T = ΔS/ΔQ.
this is the speed of movement of molecules and also with the condition that it can be detected in the infrared range of the electromagnetic wave radiation spectrum.
Therefore, the temperature at an altitude of 1000 km from the Earth is thousands of degrees Celsius, but there it is not felt due to the rarefied atmosphere.
This is the energy of chaotic microscopic motion per degree of freedom.
The point is that chaotic motion eventually spreads to all “degrees of freedom,” that is, to all possible modes of movement. For example, if a molecule can move in three directions and rotate in three directions, then over time the energy will be evenly distributed across all six movements.
If a molecule can also vibrate like a spring, then energy will penetrate into this movement. If a molecule can emit photons, then chaos will penetrate there too - the molecule will begin to chaotically emit photons.
Eventually, when everything settles down, all possible forms of motion are equally involved - this is called "thermodynamic equilibrium". In this state, how much energy falls on one degree (and each degree accounts for the same amount of energy) is called “temperature”. Only, to convert from joules to degrees, you also need to divide by Boltzmann’s constant.
If two substances whose molecules have different numbers of degrees of freedom are supplied with the same amount of energy, then the substance with more degrees of freedom will be colder. Heat flows from hotter to colder, therefore, where there are more degrees of freedom, energy is directed there.
Anatoly Khapilin
This is a conditional measure for determining the degree of excitation of the akasha plasma around the planet, which in turn moves the molecules of the structures at the place of its excitation. For example, fire, as an element of etheric matter, is more energetic than physical elements, and therefore, it excites locally a plasma that permeates everything and everyone, as well as space in a structure that, for example, should burn, and it begins to destroy electronic connections structures. The weaker the latter, the faster this structure will collapse. And the higher the degree of excitation of the plasma during combustion, for example, of gas, the more energetic it is. More details in the source.
Evgeniy Dyubailo
Temperature is a physical quantity that characterizes the average kinetic energy of particles of a macroscopic system in a state of thermodynamic equilibrium.
Simply put, temperature is a measure of energy
Temperature (in physics) Temperature(from Latin temperatura - proper mixing, proportionality, normal state), a physical quantity characterizing the state of thermodynamic equilibrium of a macroscopic system. T. is the same for all parts of an isolated system located in thermodynamic equilibrium.
If an isolated system is not in equilibrium, then over time the transition of energy (heat transfer) from more heated parts of the system to less heated ones leads to the equalization of heat throughout the entire system (the first postulate, or the zero beginning thermodynamics). T. defines: the distribution of particles forming a system over energy levels(cm. Boltzmann statistics) and particle velocity distribution (see. Maxwell distribution); degree of ionization of a substance (see Sakha formula); properties of equilibrium electromagnetic radiation of bodies - spectral radiation density (see. Planck's law of radiation), total volumetric radiation density (see. Stefan-Boltzmann radiation law) etc. T., included as a parameter in the Boltzmann distribution, is often called excitation T., in the Maxwell distribution - kinetic T., in Saha's formula - ionization T., in the Stefan-Boltzmann law - radiation temperature.
Since for a system in thermodynamic equilibrium all these parameters are equal to each other, they are simply called the temperature of the system. IN kinetic theory of gases and other sections of statistical mechanics, T. is quantitatively determined so that the average kinetic energy of the translational motion of a particle (having three degrees of freedom) is equal to T, where k is Boltzmann constant, T- Body temperature. In the general case, energy is defined as the derivative of the energy of the body as a whole according to its entropy This temperature is always positive (since the kinetic energy is positive); it is called absolute temperature or temperature on the thermodynamic temperature scale. Per unit of absolute T. in International System of Units(SI) accepted kelvin(TO). T. is often measured on the Celsius scale (t), the values of t are related to T by the equality t = T √ 273.15 K (a degree Celsius is equal to Kelvin). Methods for measuring T. are discussed in articles Thermometry, Thermometer.
Only the equilibrium state of bodies is characterized by a strictly defined temperature. There are, however, systems whose state can be approximately characterized by several unequal temperatures. For example, in a plasma consisting of light (electrons) and heavy (ions) charged particles, when particles collide, energy is quickly transferred from electrons to electrons and from ions to ions, but slowly from electrons to ions and back. There are states of plasma in which individual systems of electrons and ions are close to equilibrium, and it is possible to introduce T. electron T uh and T. ions T And , not matching each other.
In bodies whose particles have magnetic moment,
energy is usually transferred slowly from translational to magnetic degrees of freedom associated with the possibility of changing the direction of the magnetic moment. Due to this, there are states in which the system of magnetic moments is characterized by a temperature that does not coincide with the kinetic temperature corresponding to forward movement particles. Magnetic temperature determines the magnetic part of internal energy and can be either positive or negative (see. Negative temperature). In the process of equalizing the temperature, energy is transferred from particles (degrees of freedom) with a higher temperature to particles (degrees of freedom) with a smaller temperature, if they are both positive or negative, but in reverse direction, if one of them is positive and the other is negative. In this sense, negative T. is “higher” than any positive one.
The concept of T. is also used to characterize nonequilibrium systems (see. Thermodynamics of nonequilibrium processes). For example, brightness celestial bodies characterize brightness temperature,
spectral composition of radiation - color temperature etc.
L. F. Andreev.
Big Soviet encyclopedia. - M.: Soviet Encyclopedia. 1969-1978 .
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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 came from Latin language 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 alignment process, energy will be transferred from particles with great value 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. Planets solar system differ greatly from each other in terms of heating level. 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. Most high value The 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, in which people work, have been recorded in gold mines in South Africa. Miners work at a depth of three kilometers at a temperature of plus 65 degrees Celsius.
From equation (2.4)
it follows that the pressure of an ideal gas is proportional to its density (the density of a gas is determined by the number of molecules per unit volume) and the average kinetic energy of the translational motion of the molecules. At a constant and therefore at a constant volume V of the gas (where is the number of molecules in the vessel), the gas pressure depends only on the average kinetic energy of the molecules.
Meanwhile, it is known from experience that at a constant volume, the pressure of a gas can be changed only in one way: by heating or cooling it; When a gas is heated, its pressure increases, and when it cools, it decreases. Heated and cooled gas, like any body, is characterized by its temperature - a special value that has long been used in science, technology and in everyday life. Therefore, there must be a relationship between temperature and the average kinetic energy of molecules.
Before we figure out this connection, let's look at what temperature is as a physical quantity.
IN Everyday life temperature for us is the value that distinguishes “hot” from “cold”. And the first ideas about temperature arose from the sensations of heat and cold. We can use these familiar sensations to find out the main feature of temperature as a physical quantity.
Let's take three vessels. Let's pour it into one of them hot water, in the other - cold, and in the third - a mixture of hot and cold water. Let's put one hand, for example the right one, into a vessel with hot water, and the left hand into a vessel with cold water. Having held our hands for some time in these vessels, we will transfer them to the third vessel. What will our sensations tell us about the water in this vessel? The right hand will feel like water
it is cold, and the left one says that it is warm. But this “discrepancy” will disappear if you hold both hands in the third vessel longer. After some time, both hands will begin to experience exactly the same sensations, corresponding to the temperature of the water in the third vessel.
The whole point is that hands, having first been in vessels with hot and cold water, had different temperatures, different from one another and from the temperature in the third vessel. And it takes some time for the temperature of each hand to become equal to the temperature of the water in which they are immersed. Then the temperatures of the hands will become the same. The sensations will be the same. It is necessary, as they say, that thermal equilibrium be established in the system of bodies “right hand - left hand - water”.
This simple experiment shows that temperature is a quantity characterizing the state of thermal equilibrium: bodies in a state of thermal equilibrium have the same temperatures. Conversely, bodies with the same temperature are in thermal equilibrium with each other. And if two bodies are in thermal equilibrium with some third body, then both bodies are in thermal equilibrium with each other. This important statement is one of the basic laws of nature. And the very possibility of measuring temperature is based on it. In the experiment described, for example, we were talking about the thermal equilibrium of both hands, after each of them was in thermal equilibrium with water.
If a body or system of bodies is not in a state of thermal equilibrium and if the system is isolated (does not interact with other bodies), then after some time the state of thermal equilibrium is established by itself. The state of thermal equilibrium is the state into which any isolated system passes. Once such a state is reached, it no longer changes and no macroscopic changes occur in the system. One of the signs of a state of thermal equilibrium is the equality of temperatures of all parts of the body or all bodies of the system. It is known that in the process of establishing thermal equilibrium, i.e., when the temperature of two bodies is equalized, heat is transferred from one body to another. Consequently, from an experimental point of view, the temperature of a body is a quantity that determines whether it will transfer heat to another body with a different temperature or receive heat from it.
Temperature occupies a somewhat special place among physical quantities. This is not surprising, considering that in the era when this quantity appeared in science, it was not known what exactly internal processes in the substance cause sensations of heat and cold.
The uniqueness of temperature as a physical quantity lies primarily in the fact that, unlike many other quantities,
not additive. This means that if you mentally divide a body into parts, then the temperature of the whole body is not equal to the sum of the temperatures of its parts. In this way, temperature differs from, for example, quantities such as length, volume, mass, the values of which for the entire body are composed of the values of the corresponding quantities for its parts.
As a result, body temperature cannot be measured directly, as length or mass is measured, i.e., by comparison with a standard. If it can be said of one rod that its length is so many times greater than the length of another rod, then the question of how many times one temperature is contained in another does not make sense.
To measure temperature, it has long been used that when the temperature of a body changes, its properties also change. Consequently, the quantities characterizing these properties change. Therefore, to create a device that measures temperature, i.e., a thermometer, a substance (thermometric substance) and a certain quantity characterizing the property of the substance (thermometric quantity) are selected. The choice of both is completely arbitrary. In household thermometers, for example, the thermometric substance is mercury, and the thermometric quantity is the length of the mercury column.
In order for the temperature value to be associated with certain numerical values, it is also necessary to specify one or another dependence of the thermometric value on temperature. The choice of this dependence is also arbitrary: after all, while there is no thermometer, it is impossible to establish this dependence experimentally! In the case of a mercury thermometer, for example, linear dependence the length of the mercury column (volume of mercury) on temperature.
It remains to establish the unit of temperature - a degree (although in principle it could be expressed in the same units in which a thermometric value is measured, for example, using a mercury thermometer - in centimeters!). The degree value is also chosen arbitrarily (as is the thermometric substance, the thermometric value and the type of function connecting the thermometric value with temperature). The degree size is set as follows. They choose, again arbitrarily, two temperatures (they are called reference points) - usually these are the temperatures of melting ice and boiling water at atmospheric pressure - and divide this temperature interval into a certain (also arbitrary) number of equal parts - degrees, and one of these two temperatures are assigned a specific numerical value. This determines the value of the second temperature and any intermediate one. In this way a temperature scale is obtained. It is clear that using the described procedure it is possible to obtain countless different thermometers and temperature scales,
Modern thermometry is based on the ideal gas scale, established using a gas thermometer. Basically, a gas thermometer is a closed vessel filled with an ideal gas and equipped with a pressure gauge to measure the pressure of the gas. This means that the thermometric substance in such a thermometer is an ideal gas, and the thermometric quantity is the gas pressure at constant volume. The dependence of pressure on temperature is assumed (precisely accepted!) to be linear. This assumption leads to the fact that the ratio of pressures at the temperatures of boiling water and melting ice is equal to the ratio of these temperatures themselves:
The attitude is easy to determine from experience. Numerous measurements have shown that
This, therefore, is the value of the temperature ratio:
The degree size is chosen by dividing the difference into one hundred parts:
From the last two equalities it follows that the melting temperature of ice on the scale we have chosen is equal to 273.15 degrees, and the boiling point of water Tk is equal to 373.15 degrees. In order to measure the temperature of a body using a gas thermometer, it is necessary to bring the body into contact with the gas thermometer and, after waiting for equilibrium, measure the gas pressure in the thermometer. Then body temperature is determined by the formula
where is the gas pressure in a thermometer placed in melting ice.
In practice, a gas thermometer is used extremely rarely. It is entrusted with a more responsible role - all used thermometers are calibrated according to it.
The temperature equal to zero on our scale is obviously the temperature at which the pressure of an ideal gas would be zero. (This does not mean that an ideal gas can actually be cooled so much that its pressure becomes zero.) If at zero of the temperature scale the thermometric quantity becomes zero, then such a scale is called an absolute scale, and the temperature measured on such a scale is called absolute temperature. The gas thermometer scale described here is absolute. It is often also called the Kelvin scale,
and the unit of temperature in this scale is the degree Kelvin or simply kelvin (symbol: K).
In technology and everyday life, a temperature scale is often used, which differs from the one described in that the temperature of ice melting is assigned a value of zero (at the same degree size). This scale is called the Celsius scale. The temperature measured on this scale is related to absolute temperature by an obvious relationship:
In what follows we will use the Kelvin scale.
From what has been said here, it follows that temperature characterizes the thermal equilibrium of bodies: upon transition to a state of equilibrium, the temperatures of bodies are leveled off, and in a state of equilibrium, the temperature of all parts of a body or system of bodies is the same. The procedure for measuring temperature itself is connected with this. Indeed, in order to measure the value of a thermometric quantity at the temperatures of melting ice and boiling water, the thermometer must be brought into a state of equilibrium with melting ice and boiling water, and in order to measure the temperature of any body, it is necessary to ensure the possibility of establishing thermal equilibrium between the thermometer and the body . And only when such equilibrium is achieved can we consider that the body temperature is equal to the temperature measured by the thermometer.
So, temperature is what equalizes in the process of establishing equilibrium in the system. But the very concept of alignment means that something is transferred from one part of the system to another. The equation (2.4) we obtained for the pressure of an ideal gas will allow us to understand what this “something” is.
Let us imagine an insulated cylinder with an ideal gas in which thermal equilibrium has already been established, so that the temperature in all parts of the gas volume is the same. Let us assume that, without disturbing the equilibrium, a movable piston is placed in the cylinder, dividing the volume of gas into two parts (Fig. 3, a). Under equilibrium conditions, the piston will be at rest. This means that at equilibrium, not only the temperatures, but also the pressures on both sides of the piston are the same. According to equation (2.4), the quantities are also the same
Let us now temporarily break the insulation of our gas cylinder and heat one of its parts, for example the one on the left side of the piston, after which we will restore the insulation again. Now the gas in the cylinder is not in equilibrium - the temperature in the left compartment is higher than in the right (Fig. 3, b). But the gas is isolated, and the transition to a state of equilibrium will begin by itself. At the same time, we will see that the piston will begin to move from left to right. This means that work is done and, therefore, energy is transferred from the gas in the left compartment to the gas in the right through the piston. This means that what is transferred in the process of establishing thermal equilibrium is energy. After some time, the movement of the piston will stop. But the piston will stop after a series of vibrations. And it will stop in the same place where it was before the left cylinder compartment was heated. A state of equilibrium was again established in the gas cylinder. But now the temperature of the gas and its pressure are, of course, higher than before heating.
Since the piston stopped in the same place, the concentration of molecules (i.e., the number of molecules per unit volume) remained the same. This means that as a result of heating the gas, only the average kinetic energy of its molecules changed. Temperature equalization, therefore, means equalization of the average kinetic energy of the molecules on both sides of the piston. During the transition to equilibrium, energy is transferred from one part of the gas to another, but it is not the energy of the entire gas as a whole that is equalized, but the average kinetic energy per molecule. It is the average kinetic energy of a molecule that behaves like temperature.
These two quantities are also similar in that the average kinetic energy, like temperature, is not an additive quantity; it is the same for the entire gas and for any part of it (containing a sufficiently large number of molecules). The energy of the entire gas is, of course, an additive quantity - it consists of the energies of its parts.
We should not think that our reasoning applies only to the case when the gas in the cylinder is divided into two parts by a piston. And without a piston, molecules would exchange energy during collisions with each other and it would be transferred from a more heated part to a less heated one, as a result of which the average kinetic energies of the molecules would be equalized. The piston only makes the transfer of energy seem visible, since its movement is associated with the performance of work.
The above simple, although not very rigorous, reasoning shows that the quantity long known as temperature actually represents the average kinetic energy of the translational motion of molecules. The fact that we obtained this result for the case of an ideal gas does not change
When applied to an ideal gas, it is more convenient to assume that the temperature is equal to two-thirds of the average kinetic energy of the molecules, since this will simplify the form of formula (2.4) for the gas pressure. Having designated the temperature determined in this way by a letter, we can write:
Then equation (2.4) will take the simple form:
With this definition of temperature, it obviously must be measured in energy units (in the SI system - in joules, in the CGS unit system - in ergs). However, in practice it is inconvenient to use such a unit of temperature. Even such a small unit of energy is too large to serve as a unit of temperature. When using it, commonly encountered temperatures would be expressed in negligibly small numbers. For example, the melting temperature of ice would be . In addition, measuring temperature expressed in ergs would be very difficult.
For this reason, and also because the value of temperature was used long before molecular kinetic concepts were developed, which explained the true meaning of temperature, it is still measured in old units - degrees, despite the conventionality of this unit.
But if you measure temperature in degrees, then you need to enter an appropriate coefficient that converts energy units and degrees. It is usually denoted by the letter Then the relationship between temperature, measured in degrees, and average kinetic energy is expressed by the equality:
Let us recall that formula (3.1) refers to a molecule, which we agreed to consider similar to a point. Its kinetic energy is the kinetic energy of translational motion, the speed of which can be decomposed into three components. Due to the chaotic nature of molecular movements, it can be assumed that the energy
molecules is evenly distributed over all three components of speed, so that each of them accounts for energy
The factor expressing the relationship between the unit of energy and the unit of temperature - kelvin - is called Boltzmann's constant. It is clear that its numerical value must be established experimentally. Due to the special importance of this constant, it has been determined by many methods. We present the most accurate value of this constant to date. In SI units
In the GHS system of units
From formula (3.1) it follows that the zero temperature is the temperature at which the average kinetic energy erratic movements molecules is zero, that is, the temperature at which the chaotic movements of molecules stop. This is the absolute zero, the beginning of absolute temperature, which was mentioned above.
It also follows from formula (3.1) that there cannot be negative temperatures, since kinetic energy is an essentially positive quantity. However, below, in Chap. VI, it will be shown that for certain systems it is possible to formally introduce the concept of negative temperatures. However, it cannot be said about them that these are temperatures below absolute zero and that they relate to the equilibrium state of the system.
Since temperature is determined by the average energy of motion of molecules, it, like pressure, is statistical value. You cannot talk about the “temperature” of one or a few molecules, or about “hot” or “cold” molecules. It makes no sense, for example, to talk about the temperature of a gas in outer space, where the number of molecules per unit volume is so small that they do not form a gas in the usual sense of the word, and it is impossible to talk about the average energy of motion of molecules.
The energies associated with the chaotic movements of gas particles are very small. From formula (3.1) and from the given value of the Boltzmann constant, it is clear that a temperature of 1 K corresponds to an energy equal to At the lowest temperature achieved to date (about 10 6 K), the average energy of molecules is approximately 109 joules. Even the highest artificially obtained temperature - about 100 million degrees, developing during an explosion nuclear bomb, - corresponds to the negligible energy of joule particles.
Due to the fact that temperature plays a very important role in physics and technology, it is included, along with length, mass and time, among the basic quantities of the SI system of units, and the unit of temperature, kelvin, is one of the basic units of this system (the temperature dimension is denoted by the letter c).
In SI, the unit of temperature (kelvin) is established not on the basis of the temperature interval “temperature of melting ice - temperature of boiling water”, but on the basis of the interval “absolute zero - temperature of the triple point of water”. The triple point of water is the temperature at which water, water vapor and ice are in equilibrium (see § 130). The triple point temperature of water is assigned a value of 273.16 K (exact).
Thus, 1 kelvin is equal to part of the temperature interval from absolute zero temperature to the temperature of the triple point of water.
Since the temperature of the triple point of water is 0.01 °C, the degrees in the Celsius and Kelvin scales are the same and any temperature can be expressed either in degrees Celsius or in kelvins
Temperature (in physics)
Temperature(from Latin temperatura ≈ proper mixing, proportionality, normal state), a physical quantity characterizing the state of thermodynamic equilibrium of a macroscopic system. T. is the same for all parts of an isolated system that is in thermodynamic equilibrium. If an isolated system is not in equilibrium, then over time the transition of energy (heat transfer) from more heated parts of the system to less heated ones leads to an equalization of temperature throughout the entire system (the first postulate, or the zero law of thermodynamics). T determines: the distribution of particles forming a system according to energy levels (see Boltzmann statistics) and the distribution of particles according to velocities (see Maxwell distribution); degree of ionization of a substance (see Sakha formula); properties of equilibrium electromagnetic radiation of bodies ≈ spectral radiation density (see Planck's law of radiation), total volumetric radiation density (see Stefan ≈ Boltzmann's law of radiation), etc. T., included as a parameter in the Boltzmann distribution, is often called T. excitation, in Maxwell's distribution ≈ kinetic temperature, in Saha's formula ≈ ionization temperature, in Stefan's law ≈ Boltzmann ≈ radiation temperature. Since for a system in thermodynamic equilibrium all these parameters are equal to each other, they are simply called the temperature of the system. In the kinetic theory of gases and other sections of statistical mechanics, temperature is quantified so that the average kinetic energy of the translational motion of a particle (having three degrees of freedom) is equal to T, where k ≈ Boltzmann constant, T ≈ body temperature. In the general case, energy is defined as the derivative of the energy of the body as a whole by its entropy. This temperature is always positive (since the kinetic energy is positive); it is called absolute temperature or temperature on the thermodynamic temperature scale. The unit of absolute temperature in the International System of Units (SI) is the kelvin (K). T. is often measured on the Celsius scale (t), the values of t are related to T by the equality t = T √ 273.15 K (a degree Celsius is equal to Kelvin). Methods for measuring temperature are discussed in the articles Thermometry, Thermometer.
Only the equilibrium state of bodies is characterized by a strictly defined temperature. There are, however, systems whose state can be approximately characterized by several unequal temperatures. For example, in a plasma consisting of light (electrons) and heavy (ions) charged particles, when particles collide, energy is quickly transferred from electrons to electrons and from ions to ions, but slowly from electrons to ions and back. There are states of plasma in which individual systems of electrons and ions are close to equilibrium, and it is possible to introduce the T. of electrons Te and T. of Ti ions that do not coincide with each other.
In bodies whose particles have a magnetic moment, energy is usually slowly transferred from translational to magnetic degrees of freedom associated with the possibility of changing the direction of the magnetic moment. Due to this, there are states in which the system of magnetic moments is characterized by a temperature that does not coincide with the kinetic temperature corresponding to the translational motion of particles. Magnetic temperature determines the magnetic part of internal energy and can be either positive or negative (see Negative temperature). In the process of leveling the temperature, energy is transferred from particles (degrees of freedom) with a higher temperature to particles (degrees of freedom) with a smaller temperature if they are both positive or negative, but in the opposite direction if one of them is positive and the other is negative. In this sense, negative T. is “higher” than any positive one.
The concept of thermodynamics is also used to characterize nonequilibrium systems (see Thermodynamics of nonequilibrium processes). For example, the brightness of celestial bodies is characterized by brightness temperature, the spectral composition of radiation by color temperature, etc.
