What is temperature in biology definition. Absolute temperature. Temperature units
Plan:
- Introduction
- 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 Notes
Literature
Introduction
Temperature(from lat. temperatura- proper mixing, normal state) - scalar physical quantity, which characterizes the average kinetic energy of particles of a macroscopic system per one degree of freedom, which is in a state of thermodynamic equilibrium.
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 International system units (SI) thermodynamic temperature is part 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
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 molecular kinetic theory, therefore, practical scales measure temperature in conventional units - degrees.
4.1. 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 lower limit temperature - 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.
It is important to develop, based on the thermodynamic Kelvin scale, International practical scales based on reference points - phase transitions 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 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. Freezing temperature of water at standard atmospheric pressure correspond 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. .
4.2. 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 freezing atmospheric water. The scale was proposed by Anders Celsius in 1742.
4.3. Fahrenheit
In England and especially in the USA, the Fahrenheit scale is used. Zero degrees Celsius is 32 degrees Fahrenheit, and a degree Fahrenheit is 9/5 degrees Celsius.
The current definition of the Fahrenheit scale is as follows: it is a temperature scale 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 .
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 liquid and then crystallizes into solid(helium remains in a liquid state at atmospheric pressure even at absolute zero). The movement of atoms and molecules slows down, their kinetic energy decreases. The resistance of most metals 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, night cooling earth's surface below 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
| 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 different parts bodies are 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. Receipt methods 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.
This abstract is based on an article from Russian Wikipedia. Synchronization completed 07/09/11 16:20:43
Similar abstracts: Spectrum (in physics), Space in physics, Physical quantities.
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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 the translational motion of particles. Magnetic T. determines the magnetic part internal energy and can be both positive and 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 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.
Great Soviet Encyclopedia. - M.: Soviet Encyclopedia. 1969-1978 .
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- Temperature (from the Latin temperatura - proper mixing, normal state) is a physical quantity that characterizes a thermodynamic system and quantitatively expresses the intuitive concept of different degrees of heating of bodies.
Living beings are able to perceive sensations of heat and cold directly through their senses. However, accurately determining temperature requires that temperature be measured objectively, using instruments. Such devices are called thermometers and measure the so-called empirical temperature. In the empirical temperature scale, two reference points and the number of divisions between them are established - this is how the currently used Celsius, Fahrenheit and other scales were introduced. The absolute temperature measured in Kelvin is entered one reference point at a time, taking into account the fact that in nature there is a minimum temperature limit - absolute zero. The upper temperature value is limited by the Planck temperature.
If the system is in thermal equilibrium, then the temperature of all its parts is the same. Otherwise, energy is transferred in the system from the more heated parts of the system to the less heated ones, leading to equalization of temperatures in the system, and we talk about the temperature distribution in the system or a scalar temperature field. In thermodynamics, temperature is an intensive thermodynamic quantity.
Along with thermodynamic, other definitions of temperature can be introduced in other branches of physics. The molecular kinetic theory shows that temperature is proportional to the average kinetic energy of the particles of the system. Temperature determines the distribution of particles of the system according to energy levels (see Maxwell - Boltzmann statistics), the distribution of particles according to velocities (see Maxwell distribution), the degree of ionization of matter (see Saha Equation), spectral radiation density (see Planck Formula), total volume radiation density (see Stefan-Boltzmann law), etc. The temperature included as a parameter in the Boltzmann distribution is often called the excitation temperature, in the Maxwell distribution - kinetic temperature, in the Saha formula - ionization temperature, in the Stefan-Boltzmann law - radiation temperature. For a system in thermodynamic equilibrium, all these parameters are equal to each other, and they are simply called the temperature of the system.
In the International System of Quantities (ISQ), thermodynamic temperature is chosen as one of the seven basic physical quantities of the system. In the International System of Units (SI), which is based on the International System of Units, the unit for this temperature, the kelvin, is one of the seven base SI units. In the SI system and in practice, the Celsius temperature is also used; its unit is the degree Celsius (°C), equal in size to the kelvin. This is convenient, since most climatic processes on Earth and processes in living nature are associated with the range from -50 to +50 °C.
Story
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.
Since temperature is the kinetic energy of molecules, it is clear that it is most natural to measure it in energy units (i.e. 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.
Kelvin scale
Thermodynamics uses the Kelvin scale, in which temperature is measured from absolute zero (the state corresponding to the minimum theoretically possible internal energy of a body), and one kelvin is equal to 1/273.16 of the distance from absolute zero to the triple point of water (the state in which ice, water and water pairs are in equilibrium). Boltzmann's constant is used to convert kelvins into energy units. Derived units are also used: kilokelvin, megakelvin, millikelvin, etc.
Celsius
In everyday life, the Celsius scale is used, in which 0 is the freezing point of water, and 100° is the boiling point of water at atmospheric pressure. Since the freezing and boiling points of water are not well defined, the Celsius scale is currently defined using the Kelvin scale: a degree Celsius is equal to a kelvin, absolute zero is taken to be −273.15 °C. The Celsius scale is practically very convenient because water is very common on our planet and our life is based on it. Zero Celsius is a special point for meteorology, since the freezing of atmospheric water changes everything significantly.
Fahrenheit
In England and especially in the USA, the Fahrenheit scale is used. In this scale, the interval from the temperature itself is divided into 100 degrees. cold winter in the city where Fahrenheit lived, to the temperature of the human body. Zero degrees Celsius is 32 degrees Fahrenheit, and a degree Fahrenheit is equal to 5/9 degrees Celsius.
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. Fahrenheit temperature is related to Celsius temperature (t °C) by the ratio t °C = 5/9 (t °F - 32), that is, a change in temperature of 1 °F corresponds to a change of 5/9 °C. Proposed by G. Fahrenheit in 1724.
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.
|
Conversion of temperature between main scales |
|||
|
Kelvin |
Celsius |
Fahrenheit |
|
|
Kelvin (K) |
C + 273.15 |
= (F + 459.67) / 1.8 |
|
|
Celsius (°C) |
K − 273.15 |
= (F − 32) / 1.8 |
|
|
Fahrenheit (°F) |
K 1.8 − 459.67 |
C 1.8 + 32 |
|
Comparison of temperature scales
|
Description |
Kelvin | Celsius |
Fahrenheit |
Newton | Reaumur |
|
Absolute zero |
−273.15 |
−459.67 |
−90.14 |
−218.52 |
|
|
Melting temperature of a mixture of Fahrenheit (salt and ice in equal quantities) |
255.37 |
−17.78 |
−5.87 |
−14.22 |
|
| Freezing point of water (normal conditions) |
273.15 |
||||
|
Average human body temperature ¹ |
310.0 |
36.8 |
98.2 |
12.21 |
29.6 |
|
Boiling point of water (normal conditions) |
373.15 |
||||
| Solar surface temperature |
5800 |
5526 |
9980 |
1823 |
4421 |
¹ Normal 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. Since this value is not within the range of normal temperature according to modern concepts, we can say that it contains excessive (incorrect) accuracy. Some values in this table have been rounded.
Comparison of Fahrenheit and Celsius scales
(oF- Fahrenheit scale, oC- Celsius scale)
|
oF |
oC |
oF |
oC |
oF |
oC |
oF |
oC |
|||
|
459.67 |
273.15 |
60 |
51.1 |
4 |
20.0 |
20 |
6.7 |
To convert degrees Celsius to Kelvin, you must use the formula T=t+T 0 where T is the temperature in kelvins, t is the temperature in degrees Celsius, T 0 =273.15 kelvins. The size of a degree Celsius is equal to Kelvin.
Plan:
- Introduction
- 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 Notes
Literature
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
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.
4.1. 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, 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.
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 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.
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. .
4.2. 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.
4.3. Fahrenheit
In England and especially in the USA, the Fahrenheit scale is used. Zero degrees Celsius is 32 degrees Fahrenheit, and a degree Fahrenheit is 9/5 degrees Celsius.
The current definition of the Fahrenheit scale is as follows: it is a temperature scale 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 .
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
| 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.
This abstract is based on an article from Russian Wikipedia. Synchronization completed 07/09/11 16:20:43
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