Story
The word "temperature" arose at a time when people believed that hotter bodies contained a greater amount of a special substance - caloric than less heated ones. Therefore, temperature was perceived as the strength of a mixture of body substance and caloric. For this reason, the units of measure for the strength of alcoholic beverages and temperature are called the same - degrees.
From the fact that temperature is the kinetic energy of molecules, it is clear that it is most natural to measure it in energy units (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
In thermodynamics, the Kelvin scale is used, in which temperature is measured from absolute zero(state corresponding to the minimum theoretically possible internal energy 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 vapor are in equilibrium). The Boltzmann constant is used to convert kelvins to energy units. Derived units are also used: kilokelvin, megakelvin, millikelvin, etc.
Celsius
In everyday life, the Celsius scale is used, in which the freezing point of water is taken as 0, and the boiling point of water at atmospheric pressure is taken as 100 °. Since the freezing and boiling point of water is not well defined, the Celsius scale is currently defined in terms of the Kelvin scale: degrees Celsius equals kelvin, absolute zero taken as −273.15 °C. The Celsius scale is practically very convenient, since water is very common on our planet and our life is based on it. Zero Celsius is a special point for meteorology, since the freezing of atmospheric water changes everything significantly.
Fahrenheit
In England, and especially in the USA, the Fahrenheit scale is used. This scale is divided by 100 degrees from the temperature of the coldest winter in the city where Fahrenheit lived to the temperature human body. Zero degrees Celsius is 32 degrees Fahrenheit, and a degree Fahrenheit is 5/9 degrees Celsius.
The current definition of the Fahrenheit scale is as follows: it is a temperature scale, 1 degree (1 °F) of which is equal to 1/180 of the difference between the boiling point of water and the melting of ice at atmospheric pressure, and the melting point of ice is +32 °F. The temperature on the Fahrenheit scale is related to the temperature on the Celsius scale (t ° C) by the ratio t ° C \u003d 5/9 (t ° F - 32), that is, a temperature change 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.
Unit - degree Réaumur (°R), 1 °R is equal to 1/80 of the temperature interval between the reference points - the temperature of melting ice (0 °R) and boiling water (80 °R)
1°R = 1.25°C.
At present, the scale has fallen into disuse; it has been preserved for the longest time in France, in the author's homeland.
|
Temperature conversion 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 | Réaumur |
|
Absolute zero |
−273.15 |
−459.67 |
−90.14 |
−218.52 |
|
|
Melting point of Fahrenheit mixture (salt and ice in equal amounts) |
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 |
||||
| Sun 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 given value of 98.6 °F is an exact Fahrenheit conversion of the 19th century German value of 37 °C. Because this value is outside the normal temperature range for modern ideas, we can say that it contains excessive (incorrect) precision. 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 kelvins, use the formula T=t+T0 where T is the temperature in kelvins, t is the temperature in degrees Celsius, T 0 =273.15 kelvin. The degree Celsius is equal in size to Kelvin.
- 48.67 KbFederal State Budgetary Educational Institution of Higher Professional Education
"Voronezh State Pedagogical University"
Department of General Physics
on the topic: "Absolute zero temperature"
Completed by: 1st year student, FMF,
PI, Kondratenko Irina Alexandrovna
Checked by: Assistant of the Department of General
physicists Afonin G.V.
Voronezh-2013
Introduction………………………………………………………. 3
1.Absolute zero…………………………………………...4
2.History………………………………………………………… 6
3. Phenomena observed near absolute zero………..9
Conclusion……………………………………………………… 11
List of used literature…………………………..12
Introduction
For many years, researchers have been attacking the absolute zero temperature. As you know, the temperature equal to absolute zero characterizes the ground state of a system of many particles - the state with the lowest possible energy, at which atoms and molecules perform the so-called "zero" vibrations. Thus, deep cooling close to absolute zero (it is believed that absolute zero itself is unattainable in practice) opens up unlimited possibilities for studying the properties of matter.
1. Absolute zero
Absolute zero temperature (more rarely - absolute zero temperature) - the minimum temperature limit that a physical body in the Universe. Absolute zero serves as the reference point for an absolute temperature scale, such as the Kelvin scale. In 1954, the X General Conference on Weights and Measures established a thermodynamic temperature scale with one reference point - the triple point of water, the temperature of which is taken to be 273.16 K (exactly), which corresponds to 0.01 ° C, so that on the Celsius scale absolute zero corresponds to temperature -273.15°C.
In the framework of the applicability of thermodynamics, absolute zero is unattainable in practice. Its existence and position on the temperature scale follows from the extrapolation of the observed physical phenomena, while such extrapolation shows that at absolute zero, the energy of the thermal motion of molecules and atoms of a substance must be equal to zero, that is, the chaotic motion of particles stops, and they form an ordered structure, occupying a clear position in the nodes of the crystal lattice (liquid helium is an exception). However, from the point of view quantum physics and at absolute zero temperature there are zero fluctuations, which are due to the quantum properties of particles and the physical vacuum surrounding them.
As the temperature of the system tends to absolute zero, its entropy, heat capacity, thermal expansion coefficient also tend to zero, and the chaotic motion of the particles that make up the system stops. In a word, matter becomes supersubstance with superconductivity and superfluidity.
The absolute zero temperature is unattainable in practice, and obtaining temperatures approaching it as close as possible is a complex experimental problem, but temperatures have already been obtained that are only millionths of a degree away from absolute zero. .
Let us find the value of absolute zero on the Celsius scale by equating the volume V to zero and taking into account that
Hence the absolute zero temperature is -273°C.
This is the limiting, lowest temperature in nature, that “greatest or last degree of cold”, the existence of which Lomonosov predicted.
Fig.1. Absolute scale and Celsius scale
The SI unit of absolute temperature is called the kelvin (abbreviated as K). Therefore, one degree Celsius is equal to one degree Kelvin: 1 °C = 1 K.
Thus, the absolute temperature is a derivative quantity that depends on the Celsius temperature and on the experimentally determined value of a. However, it is of fundamental importance.
From the point of view of the molecular kinetic theory, the absolute temperature is related to the average kinetic energy of the random motion of atoms or molecules. At T = 0 K, the thermal motion of molecules stops.
2. History
The physical concept of "absolute zero temperature" is very important for modern science: such a concept as superconductivity, the discovery of which made a splash in the second half of the 20th century, is closely related to it.
To understand what absolute zero is, one should refer to the works of such famous physicists as G. Fahrenheit, A. Celsius, J. Gay-Lussac and W. Thomson. It was they who played a key role in the creation of the main temperature scales still used today.
The first to offer his own temperature scale in 1714 was the German physicist G. Fahrenheit. At the same time, the temperature of the mixture, which included snow and ammonia, was taken as absolute zero, that is, the lowest point on this scale. The next important indicator was the normal temperature of the human body, which began to equal 1000. Accordingly, each division of this scale was called the “degree Fahrenheit”, and the scale itself was called the “Fahrenheit scale”.
After 30 years, the Swedish astronomer A. Celsius proposed his own temperature scale, where the main points were the melting temperature of ice and the boiling point of water. This scale was called the "Celsius scale", it is still popular in most countries of the world, including Russia.
In 1802, while conducting his famous experiments, the French scientist J. Gay-Lussac discovered that the volume of a gas mass at constant pressure is directly dependent on temperature. But the most curious thing was that when the temperature changed by 10 Celsius, the volume of the gas increased or decreased by the same amount. Having made the necessary calculations, Gay-Lussac found that this value was equal to 1/273 of the volume of gas. From this law, the obvious conclusion followed: the temperature equal to -273 ° C is the lowest temperature, even approaching which it is impossible to reach it. This temperature is called "absolute zero temperature". Moreover, absolute zero became the starting point for creating the absolute temperature scale, in which the English physicist W. Thomson, also known as Lord Kelvin, took an active part. His main research concerned the proof that no body in nature can be cooled below absolute zero. At the same time, he actively used the second law of thermodynamics, therefore, the absolute temperature scale introduced by him in 1848 began to be called the thermodynamic or “Kelvin scale.” In subsequent years and decades, only the numerical refinement of the concept of “absolute zero” took place.
Fig.2. Relationship between Fahrenheit (F), Celsius (C) and Kelvin (K) temperature scales.
It is also worth noting that absolute zero plays a very important role in the SI system. The thing is that in 1960 at the next General Conference on Weights and Measures, the unit of thermodynamic temperature - kelvin - became one of the six basic units of measurement. At the same time, it was specifically stipulated that one degree Kelvin
is numerically equal to one degree Celsius, only here the reference point "according to Kelvin" is considered to be absolute zero.
The main physical meaning of absolute zero is that, according to the basic physical laws, at such a temperature, the energy of motion of elementary particles, such as atoms and molecules, is equal to zero, and in this case, any chaotic motion of these very particles should stop. At a temperature equal to absolute zero, atoms and molecules should take a clear position in the main points of the crystal lattice, forming an ordered system.
Currently, using special equipment, scientists have been able to obtain a temperature only a few millionths higher than absolute zero. It is physically impossible to achieve this value itself because of the second law of thermodynamics.
3. Phenomena observed near absolute zero
At temperatures close to absolute zero, purely quantum effects can be observed at the macroscopic level, such as:
1. Superconductivity - the property of some materials to have strictly zero electrical resistance when they reach a temperature below a certain value (critical temperature). Several hundreds of compounds, pure elements, alloys and ceramics are known that pass into the superconducting state.
Superconductivity is a quantum phenomenon. It is also characterized by the Meissner effect, which consists in the complete displacement of the magnetic field from the bulk of the superconductor. The existence of this effect shows that superconductivity cannot be described simply as ideal conductivity in the classical sense. Opening in 1986-1993 a number of high-temperature superconductors (HTSCs) pushed far the temperature limit of superconductivity and allowed the practical use of superconducting materials not only at the temperature of liquid helium (4.2 K), but also at the boiling point of liquid nitrogen (77 K), a much cheaper cryogenic liquid.
2. Superfluidity - the ability of a substance in a special state (quantum liquid), which occurs when the temperature drops to absolute zero (thermodynamic phase), to flow through narrow slots and capillaries without friction. Until recently, superfluidity was known only for liquid helium, but in last years superfluidity was also discovered in other systems: in rarefied atomic Bose condensates, solid helium.
Superfluidity is explained as follows. Since helium atoms are bosons, quantum mechanics allows an arbitrary number of particles to be in the same state. Near absolute zero temperatures, all helium atoms are in the ground energy state. Since the energy of the states is discrete, an atom can receive not any energy, but only one that is equal to the energy gap between neighboring energy levels. But at low temperatures, the collision energy may be less than this value, as a result of which energy dissipation simply will not occur. The fluid will flow without friction.
3. Bose - Einstein condensate - state of aggregation a substance based on bosons cooled to temperatures close to absolute zero (less than a millionth of a degree above absolute zero). In such a highly chilled state, it is enough big number atoms are in their lowest possible quantum states and quantum effects begin to manifest themselves at the macroscopic level.
Conclusion
The study of the properties of matter near absolute zero is of great interest to science and technology.
Many properties of a substance, veiled at room temperature by thermal phenomena (for example, thermal noise), begin to manifest themselves more and more as the temperature decreases, allowing one to study in its pure form the regularities and relationships inherent in a given substance. Research in the field of low temperatures made it possible to discover many new natural phenomena, such as, for example, the superfluidity of helium and the superconductivity of metals.
At low temperatures, the properties of materials change dramatically. Some metals increase their strength, become ductile, others become brittle, like glass.
The study of physicochemical properties at low temperatures will make it possible in the future to create new substances with predetermined properties. All this is very valuable for the design and construction of spacecraft, stations and instruments.
It is known that during radar studies of cosmic bodies, the received radio signal is very small and it is difficult to distinguish it from various noises. Molecular oscillators and amplifiers recently created by scientists operate at very low temperatures and therefore have a very low noise level.
Low temperature electrical and magnetic properties metals, semiconductors and dielectrics make it possible to develop fundamentally new radio engineering devices of microscopic dimensions.
Extremely low temperatures are used to create the vacuum required, for example, for the operation of giant nuclear particle accelerators.
Bibliography
- http://wikipedia.org
- http://rudocs.exdat.com
- http://fb.ru
Short description
For many years, researchers have been attacking the absolute zero temperature. As you know, the temperature equal to absolute zero characterizes the ground state of a system of many particles - the state with the lowest possible energy, at which atoms and molecules perform the so-called "zero" vibrations. Thus, deep cooling close to absolute zero (it is believed that absolute zero itself is unattainable in practice) opens up unlimited possibilities for studying the properties of matter.
When the weather report predicts temperatures around zero, you should not go to the skating rink: the ice will melt. The melting temperature of ice is taken as zero degrees Celsius - the most common temperature scale.
We are well aware of the negative degrees of the Celsius scale - degrees<ниже
нуля>, degrees of cold. The lowest temperature on Earth was recorded in Antarctica: -88.3°C. Outside the Earth, even lower temperatures are possible: on the surface of the Moon at lunar midnight it can reach -160°C.
But nowhere can there be arbitrarily low temperatures. Extremely low temperature - absolute zero - on the Celsius scale corresponds to - 273.16 °.
The absolute temperature scale, the Kelvin scale, originates from absolute zero. Ice melts at 273.16° Kelvin, and water boils at 373.16° K. Thus, degree K is equal to degree C. But on the Kelvin scale, all temperatures are positive.
Why is 0°K the limit of cold?
Heat is the chaotic movement of atoms and molecules of matter. When a substance is cooled, thermal energy is taken away from it, and in this case, the random movement of particles weakens. In the end, with strong cooling, thermal<пляска>particles almost completely stops. Atoms and molecules would freeze completely at a temperature that is taken as absolute zero. According to the principles quantum mechanics, at absolute zero, it is precisely the thermal motion of particles that would stop, but the particles themselves would not freeze, since they cannot be completely at rest. Thus, at absolute zero, the particles must still retain some kind of motion, which is called zero.
However, to cool a substance to a temperature below absolute zero is an idea as meaningless as, say, the intention<идти медленнее, чем стоять на месте>.
Moreover, even reaching exact absolute zero is also almost impossible. You can only get closer to him. Because absolutely all of its thermal energy cannot be taken away from a substance by any means. Some of the thermal energy remains during the deepest cooling.
How do they reach ultra-low temperatures?
Freezing a substance is more difficult than heating it. This can be seen at least from a comparison of the design of the stove and refrigerator.
In most household and industrial refrigerators, heat is removed due to the evaporation of a special liquid - freon, which circulates through metal tubes. The secret is that freon can remain in a liquid state only at a sufficiently low temperature. In the refrigerating chamber, due to the heat of the chamber, it heats up and boils, turning into steam. But the steam is compressed by the compressor, liquefied and enters the evaporator, making up for the loss of evaporating freon. Energy is used to run the compressor.
In deep-cooling devices, the carrier of cold is a supercold liquid - liquid helium. Colorless, light (8 times lighter than water), it boils under atmospheric pressure at 4.2°K, and in vacuum at 0.7°K. An even lower temperature is given by the light isotope of helium: 0.3°K.
It is quite difficult to arrange a permanent helium refrigerator. Research is carried out simply in liquid helium baths. And to liquefy this gas, physicists use different techniques. For example, pre-cooled and compressed helium is expanded by releasing it through a thin hole into a vacuum chamber. At the same time, the temperature still decreases and some part of the gas turns into a liquid. It is more efficient not only to expand the cooled gas, but also to make it do work - to move the piston.
The resulting liquid helium is stored in special thermoses - Dewar vessels. The cost of this coldest liquid (the only one that does not freeze at absolute zero) is quite high. Nevertheless, liquid helium is now being used more and more widely, not only in science, but also in various technical devices.
The lowest temperatures were achieved in a different way. It turns out that the molecules of some salts, such as potassium chromium alum, can rotate along the force magnetic lines. This salt is preliminarily cooled with liquid helium to 1°K and placed in a strong magnetic field. In this case, the molecules rotate along the lines of force, and the released heat is taken away by liquid helium. Then the magnetic field is sharply removed, the molecules again turn in different directions, and the spent
this work leads to further cooling of the salt. Thus, a temperature of 0.001°K was obtained. By a similar method in principle, using other substances, one can obtain an even lower temperature.
The lowest temperature obtained so far on Earth is 0.00001°K.
Substance frozen to ultra-low temperatures in liquid helium baths changes markedly. Rubber becomes brittle, lead becomes hard as steel and resilient, many alloys increase strength.
Liquid helium itself behaves in a peculiar way. At temperatures below 2.2 °K, it acquires a property unprecedented for ordinary liquids - superfluidity: some of it completely loses viscosity and flows without any friction through the narrowest slots.
This phenomenon, discovered in 1937 by the Soviet physicist Academician P. JI. Kapitsa, was then explained by Academician JI. D. Landau.
It turns out that at ultralow temperatures, the quantum laws of the behavior of matter begin to noticeably affect. As one of these laws requires, energy can be transferred from body to body only in quite definite portions-quanta. There are so few heat quanta in liquid helium that there are not enough of them for all atoms. Part of the liquid, devoid of heat quanta, remains at absolute zero temperature, its atoms do not participate in random thermal motion at all and do not interact with the vessel walls in any way. This part (it was called helium-H) possesses superfluidity. As the temperature decreases, helium-II becomes more and more, and at absolute zero, all helium would turn into helium-N.
Superfluidity has now been studied in great detail and has even found a useful practical use: with its help it is possible to separate helium isotopes.
Near absolute zero, extremely curious changes occur in the electrical properties of certain materials.
In 1911, the Dutch physicist Kamerling-Onnes made an unexpected discovery: it turned out that at a temperature of 4.12 ° K, electrical resistance completely disappears in mercury. Mercury becomes a superconductor. The electric current induced in the superconducting ring does not decay and can flow almost forever.
Above such a ring, a superconducting ball will float in the air and not fall, as if from a fairy tale.<гроб Магомета>, because its heaviness is compensated by the magnetic repulsion between the ring and the ball. After all, the undamped current in the ring will create a magnetic field, and it, in turn, will induce an electric current in the ball and, along with it, an oppositely directed magnetic field.
In addition to mercury, tin, lead, zinc, and aluminum have superconductivity near absolute zero. This property has been found in 23 elements and over a hundred different alloys and other chemical compounds.
The temperatures at which superconductivity appears (critical temperatures) are in a fairly wide range, from 0.35°K (hafnium) to 18°K (niobium-tin alloy).
The phenomenon of superconductivity, as well as super-
fluidity, studied in detail. The dependences of critical temperatures on the internal structure of materials and the external magnetic field are found. A deep theory of superconductivity was developed (an important contribution was made by the Soviet scientist Academician N. N. Bogolyubov).
The essence of this paradoxical phenomenon is again purely quantum. At ultralow temperatures, electrons in
superconductor form a system of pairwise connected particles that cannot give energy to the crystal lattice, spend energy quanta to heat it. Pairs of electrons move like<танцуя>, between<прутьями решетки>- ions and bypass them without collisions and energy transfer.
Superconductivity is increasingly being used in technology.
For example, superconducting solenoids are coming into practice - superconductor coils immersed in liquid helium. Once induced current and, consequently, the magnetic field can be stored in them for an arbitrarily long time. It can reach a gigantic value - over 100,000 oersted. In the future, powerful industrial superconducting devices will undoubtedly appear - electric motors, electromagnets, etc.
In radio electronics, ultrasensitive amplifiers and generators of electromagnetic waves begin to play a significant role, which work especially well in baths with liquid helium - there the internal<шумы>equipment. In electronic computing technology, a bright future is promised for low-power superconducting switches - cryotrons (see Art.<Пути электроники>).
It is not difficult to imagine how tempting it would be to advance the operation of such devices to higher, more accessible temperatures. Recently, the hope of creating polymer film superconductors has been opened up. The peculiar nature of electrical conductivity in such materials promises a brilliant opportunity to maintain superconductivity even at room temperatures. Scientists are persistently looking for ways to realize this hope.
And now let's look into the realm of the hottest thing in the world - into the bowels of the stars. Where temperatures reach millions of degrees.
The chaotic thermal motion in stars is so intense that whole atoms cannot exist there: they are destroyed in countless collisions.
Therefore, a substance so strongly heated cannot be either solid, liquid, or gaseous. It is in the state of plasma, i.e., a mixture of electrically charged<осколков>atoms - atomic nuclei and electrons.
Plasma is a kind of state of matter. Since its particles are electrically charged, they sensitively obey electric and magnetic forces. Therefore, the close proximity of two atomic nuclei (they carry a positive charge) is a rare phenomenon. Only when high densities and huge temperatures bumping into each other atomic nuclei able to get close. Then thermonuclear reactions take place - the source of energy for stars.
The closest star to us - the Sun consists mainly of hydrogen plasma, which is heated in the bowels of the star up to 10 million degrees. Under such conditions, close encounters of fast hydrogen nuclei - protons, though rare, do happen. Sometimes approaching protons interact: having overcome electrical repulsion, they fall into the power of giant nuclear forces attraction, fast<падают>each other and merge. Here an instant restructuring takes place: instead of two protons, a deuteron (the nucleus of a heavy isotope of hydrogen), a positron and a neutrino appear. The energy released is 0.46 million electron volts (Mev).
Each individual solar proton can enter into such a reaction on average once in 14 billion years. But there are so many protons in the bowels of the luminary that here and there this unlikely event takes place - and our star burns with its even, dazzling flame.
The synthesis of deuterons is only the first step in solar thermonuclear transformations. The newborn deuteron very soon (on average after 5.7 seconds) combines with one more proton. There is a core of light helium and a gamma quantum of electromagnetic radiation. 5.48 MeV of energy is released.
Finally, on average, once every million years, two nuclei of light helium can converge and fuse. Then an ordinary helium nucleus (alpha particle) is formed and two protons are split off. 12.85 MeV of energy is released.
This three-stage<конвейер>thermonuclear reactions is not the only one. There is another chain of nuclear transformations, faster ones. The atomic nuclei of carbon and nitrogen participate in it (without being consumed). But in both cases, alpha particles are synthesized from hydrogen nuclei. Figuratively speaking, the solar hydrogen plasma<сгорает>, turning into<золу>- helium plasma. And in the process of synthesis of each gram of helium plasma, 175 thousand kWh of energy are released. Great amount!
Every second, the Sun radiates 4,1033 ergs of energy, losing 4,1012 g (4 million tons) of matter in weight. But the total mass of the Sun is 2 1027 tons. This means that in a million years, due to the emission of radiation, the Sun<худеет>only one ten millionth of its mass. These figures eloquently illustrate the effectiveness of thermonuclear reactions and the gigantic calorific value of solar energy.<горючего>- hydrogen.
Thermonuclear fusion seems to be the main source of energy for all stars. At different temperatures and densities of stellar interiors, different types of reactions take place. In particular, solar<зола>- helium nuclei - at 100 million degrees it becomes thermonuclear itself<горючим>. Then even heavier atomic nuclei - carbon and even oxygen - can be synthesized from alpha particles.
According to many scientists, our entire Metagalaxy as a whole is also the fruit of thermonuclear fusion, which took place at a temperature of a billion degrees (see Art.<Вселенная вчера, сегодня и завтра>).
The extraordinary calorie content of thermonuclear<горючего>prompted scientists to seek artificial implementation of nuclear fusion reactions.
<Горючего>There are many isotopes of hydrogen on our planet. For example, superheavy hydrogen tritium can be obtained from lithium metal in nuclear reactors. And heavy hydrogen - deuterium is part of heavy water, which can be extracted from ordinary water.
Heavy hydrogen extracted from two glasses of ordinary water would provide as much energy in a fusion reactor as burning a barrel of premium gasoline now provides.
The difficulty lies in preheating<горючее>to temperatures at which it can ignite with mighty thermonuclear fire.
This problem was first solved in the hydrogen bomb. Hydrogen isotopes there are ignited by an explosion atomic bomb, which is accompanied by heating of the substance to many tens of millions of degrees. In one version of the hydrogen bomb, the thermonuclear fuel is chemical compound heavy hydrogen with light lithium - deuteride of light l and t and i. This white powder, similar to table salt,<воспламеняясь>from<спички>, which is the atomic bomb, instantly explodes and creates a temperature of hundreds of millions of degrees.
To stir up peace thermonuclear reaction, we must first learn how, without the services of an atomic bomb, to heat up small doses of a sufficiently dense plasma of hydrogen isotopes to temperatures of hundreds of millions of degrees. This problem is one of the most difficult in modern applied physics. Scientists from all over the world have been working on it for many years.
We have already said that it is the chaotic motion of particles that creates the heating of bodies, and the average energy of their random motion corresponds to the temperature. To heat up a cold body means to create this disorder in any way.
Imagine that two groups of runners are rapidly rushing towards each other. So they collided, mixed up, a crowd began, confusion. Great mess!
Approximately in the same way, physicists at first tried to obtain a high temperature - by pushing high-pressure gas jets. The gas was heated up to 10 thousand degrees. At one time it was a record: the temperature is higher than on the surface of the Sun.
But with this method, further, rather slow, non-explosive heating of the gas is impossible, since thermal disorder instantly spreads in all directions, warming the walls of the experimental chamber and the environment. The resulting heat quickly leaves the system and it is impossible to isolate it.
If the gas jets are replaced by plasma flows, the problem of thermal insulation remains very difficult, but there is also hope for its solution.
True, plasma cannot be protected from heat loss by vessels made of even the most refractory substance. In contact with solid walls, the hot plasma immediately cools down. On the other hand, one can try to hold and heat up the plasma by creating its accumulation in a vacuum so that it does not touch the walls of the chamber, but hangs in the void, without touching anything. Here one should take advantage of the fact that plasma particles are not neutral, like gas atoms, but electrically charged. Therefore, in motion, they are subject to the action of magnetic forces. The problem arises: to arrange a magnetic field of a special configuration in which the hot plasma would hang like in a bag with invisible walls.
The simplest form of such a field is created automatically when strong pulses are passed through the plasma electric current. In this case, magnetic forces are induced around the plasma filament, which tend to compress the filament. The plasma separates from the walls of the discharge tube, and the temperature rises to 2 million degrees near the axis of the filament in a rush of particles.
In our country, such experiments were carried out as early as 1950 under the guidance of Academicians JI. A. Artsimovich and M.A. Leontovich.
Another direction of experiments is the use of a magnetic bottle, proposed in 1952 by the Soviet physicist G. I. Budker, now an academician. The magnetic bottle is placed in a corktron - a cylindrical vacuum chamber equipped with an external winding, which thickens at the ends of the chamber. The current flowing through the winding creates a magnetic field in the chamber. Its lines of force in the middle part are parallel to the generatrices of the cylinder, and at the ends they are compressed and form magnetic plugs. Plasma particles injected into a magnetic bottle curl around the lines of force and are reflected from the corks. As a result, the plasma is kept inside the bottle for some time. If the energy of the plasma particles introduced into the bottle is high enough and there are enough of them, they enter into complex force interactions, their initially ordered motion becomes entangled, becomes disordered - the temperature of hydrogen nuclei rises to tens of millions of degrees.
Additional heating is achieved by electromagnetic<ударами>by plasma, magnetic field compression, etc. Now the plasma of heavy hydrogen nuclei is heated to hundreds of millions of degrees. True, this can be done either for a short time or at a low plasma density.
To excite a self-sustaining reaction, it is necessary to further increase the temperature and density of the plasma. This is difficult to achieve. However, the problem, as scientists are convinced, is undeniably solvable.
G.B. Anfilov
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Any physical body, including all objects in the Universe, has a minimum temperature index or its limit. For the reference point of any temperature scale, it is customary to consider the value of absolute zero temperatures. But this is only in theory. Chaotic movement atoms and molecules, which give up their energy at this time, have not yet been stopped in practice.
This is the main reason why absolute zero temperatures cannot be reached. There are still disputes about the consequences of this process. From the point of view of thermodynamics, this limit is unattainable, since the thermal motion of atoms and molecules stops completely, and a crystal lattice is formed.
Representatives of quantum physics provide for the presence of minimal zero-point oscillations at absolute zero temperatures.
What is the value of absolute zero temperature and why it cannot be reached
At the General Conference on Weights and Measures, for the first time, a reference or reference point was established for measuring instruments that determine temperature indicators.
Currently, in the International System of Units, the reference point for the Celsius scale is 0 ° C when freezing and 100 ° C during the boiling process, the value of absolute zero temperatures is equal to −273.15 ° C.
Using temperature values in the Kelvin scale according to the same International System of Units, boiling water will occur at a reference value of 99.975 ° C, absolute zero equates to 0. Fahrenheit on the scale corresponds to -459.67 degrees.
But, if these data are obtained, why then it is impossible to achieve absolute zero temperatures in practice. For comparison, we can take the speed of light known to everyone, which is equal to a constant physical value of 1,079,252,848.8 km/h.
However, this value cannot be achieved in practice. It depends both on the transmission wavelength, and on the conditions, and on the necessary absorption of a large amount of energy by the particles. To obtain the value of absolute zero temperatures, a large return of energy is necessary and the absence of its sources to prevent it from entering atoms and molecules.
But even in conditions of complete vacuum, neither the speed of light nor absolute zero temperatures were obtained by scientists.
Why is it possible to reach approximate zero temperatures, but not absolute
What will happen when science can come close to achieving the extremely low temperature of absolute zero, so far remains only in the theory of thermodynamics and quantum physics. What is the reason why it is impossible to reach absolute zero temperatures in practice.
All known attempts to cool the substance to the lowest limit limit due to the maximum energy loss led to the fact that the value of the heat capacity of the substance also reached a minimum value. Molecules were simply not able to give the rest of the energy. As a result, the cooling process stopped before reaching absolute zero.
When studying the behavior of metals in conditions close to the value of absolute zero temperatures, scientists have found that the maximum decrease in temperature should provoke a loss of resistance.
But the cessation of the movement of atoms and molecules only led to the formation of a crystal lattice, through which the passing electrons transferred part of their energy to the immobile atoms. It failed to reach absolute zero again.
In 2003, only half a billionth of 1°C was missing from absolute zero. NASA researchers used the Na molecule to conduct experiments, which was always in a magnetic field and gave off its energy.
The closest was the achievement of scientists from Yale University, which in 2014 achieved an indicator of 0.0025 Kelvin. The resulting compound strontium monofluoride (SrF) existed for only 2.5 seconds. And in the end, it still fell apart into atoms.
The term "temperature" appeared at a time when physicists thought that warm bodies were composed of more specific substance - caloric - than the same bodies, but cold. And the temperature was interpreted as a value corresponding to the amount of caloric in the body. Since then, the temperature of any body is measured in degrees. But in reality it is a measure of the kinetic energy of moving molecules, and, based on this, it should be measured in Joules, in accordance with the SI system of units.
The concept of "absolute zero temperature" comes from the second law of thermodynamics. According to it, the process of transferring heat from a cold body to a hot one is impossible. This concept was introduced by the English physicist W. Thomson. For achievements in physics, he was granted the noble title of "Lord" and the title of "Baron Kelvin". In 1848, W. Thomson (Kelvin) suggested using a temperature scale, in which he took the absolute zero temperature corresponding to the extreme cold as the starting point, and took degrees Celsius as the division price. The unit of Kelvin is 1/27316 of the temperature of the triple point of water (about 0 degrees C), i.e. the temperature at which pure water exists in three forms at once: ice, liquid water, and steam. temperature is the lowest possible low temperature at which the movement of molecules stops, and it is no longer possible to extract thermal energy from the substance. Since then, the absolute temperature scale has been named after him.
Temperature is measured on different scales
The most commonly used temperature scale is called the Celsius scale. It is built on two points: on the temperature of the phase transition of water from liquid to vapor and water to ice. A. Celsius in 1742 proposed to divide the distance between reference points into 100 intervals, and take water as zero, while the freezing point is 100 degrees. But the Swede K. Linnaeus suggested doing the opposite. Since then, water freezes at zero degrees A. Celsius. Although it should boil exactly in Celsius. Absolute zero in Celsius corresponds to minus 273.16 degrees Celsius.
There are several more temperature scales: Fahrenheit, Réaumur, Rankine, Newton, Roemer. They have different and price divisions. For example, the Réaumur scale is also built on the benchmarks of boiling and freezing of water, but it has 80 divisions. The Fahrenheit scale, which appeared in 1724, is used in everyday life only in some countries of the world, including the USA; one is the temperature of the mixture of water ice - ammonia and the other is the temperature of the human body. The scale is divided into one hundred divisions. Zero Celsius corresponds to 32 The conversion of degrees to Fahrenheit can be done using the formula: F \u003d 1.8 C + 32. Reverse translation: C \u003d (F - 32) / 1.8, where: F - degrees Fahrenheit, C - degrees Celsius. If you are too lazy to count, go to the online Celsius to Fahrenheit conversion service. In the box, type the number of degrees Celsius, click "Calculate", select "Fahrenheit" and click "Start". The result will appear immediately.
Named after the English (more precisely Scottish) physicist William J. Rankin, contemporary Kelvin and one of the founders of technical thermodynamics. There are three important points in his scale: the beginning is absolute zero, the freezing point of water is 491.67 degrees Rankine and the boiling point of water is 671.67 degrees. The number of divisions between the freezing of water and its boiling in both Rankine and Fahrenheit is 180.
Most of these scales are used exclusively by physicists. And 40% of American high school students surveyed these days said they don't know what absolute zero temperature is.
