What is the physical meaning of absolute zero temperature. absolute zero

29.10.2019

Any measurement requires a reference point. Temperature is no exception. For the Fahrenheit scale, such a zero mark is the temperature of snow mixed with table salt, for the Celsius scale, the freezing point of water. But there is a special temperature reference point - absolute zero.

Absolute temperature zero corresponds to 273.15 degrees Celsius below zero, 459.67 below zero Fahrenheit. For the Kelvin temperature scale, this temperature itself is the zero mark.

The essence of absolute zero temperature

The concept of absolute zero comes from the very essence of temperature. Any body has energy that it gives to the external environment during heat transfer. In this case, the body temperature decreases, i.e. there is less energy left. Theoretically, this process can continue until the amount of energy reaches such a minimum at which the body can no longer give it away.
A distant harbinger of such an idea can already be found in M.V. Lomonosov. The great Russian scientist explained heat by "rotary" motion. Therefore, the limiting degree of cooling is a complete stop of such movement.

By modern ideas, absolute zero temperature is a state of matter in which the molecules are at the lowest possible energy level. With less energy, i.e. at a lower temperature, no physical body can exist.

Theory and practice

absolute zero temperature is a theoretical concept, it is impossible to achieve it in practice, in principle, even in the conditions of scientific laboratories with the most sophisticated equipment. But scientists manage to cool the matter to very low temperatures, which are close to absolute zero.

At such temperatures, substances acquire amazing properties that they cannot have under ordinary circumstances. Mercury, which is called "living silver" because of its near-liquid state, at this temperature becomes solid - to the point that it can hammer nails. Some metals become brittle, like glass. Rubber becomes hard and brittle. If a rubber object is hit with a hammer at a temperature close to absolute zero, it will break like glass.

Such a change in properties is also associated with the nature of heat. The higher the temperature of the physical body, the more intense and chaotic the molecules move. As the temperature decreases, the movement becomes less intense, and the structure becomes more ordered. So the gas becomes a liquid, and the liquid becomes a solid. The limiting level of order is the crystal structure. At ultra-low temperatures, even substances that normally remain amorphous, such as rubber, acquire it.

Interesting phenomena occur with metals. atoms crystal lattice oscillate with a smaller amplitude, the scattering of electrons decreases, therefore, the electrical resistance decreases. The metal acquires superconductivity, practical use which seems very tempting, although difficult to achieve.

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. The chaotic movement of atoms and molecules, which give off their energy at this time, has 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 absolute zero temperature value 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 known speed of light, which is equal to a constant physical meaning 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.

14. Absolute temperature and its physical meaning
Ideal gas equation of state (Mendeleev-Clapeyron equation)

The concept of "temperature" means the degree of heating of the body.

There are several temperature scales. In the absolute (thermodynamic) scale, temperature is measured in kelvins (K). Zero in this scale is called the absolute zero of temperature, approximately equal to - 273 0 C. At absolute zero, the translational movement of molecules stops.

The thermodynamic temperature T is related to the temperature on the Celsius scale by the following relationship:
T = (t 0 + 273)K
For an ideal gas, there is a proportional relationship between the absolute temperature of the gas and the average kinetic energy forward movement molecules:
,
where k is Boltzmann's constant, k = 1.38 10 – 23 J/K

Thus, absolute temperature is a measure of the average kinetic energy of the translational motion of molecules. This is its physical meaning.

Substituting into the equation p= n expression for the average kinetic energy
= kT, we get

p= n kT = nkT
From the basic MKT equation for an ideal gas p = nkT with the substitution
,
you can get the equation
, or A kT
N A k = R is the universal gas constant, R=8.31

The equation is called the ideal gas equation of state (Mendeleev-Clapeyron equation).
^ 15. Gas laws. Plots of isoprocesses.

The isothermal process (T = const) obeys the Boyle-Mariotte law: for a given mass of gas at a constant temperature, the product of pressure and volume is a constant.

, or or

The isobaric process (p = const) obeys the Gay-Lussac law: for a given mass of gas at constant pressure, the ratio of gas volume to absolute temperature is a constant value.

Or or

The isochoric process (V = const) obeys Charles's law: for a given mass of gas at a constant volume, the ratio of gas pressure to absolute temperature is a constant value.

Or or

Internal energy of an ideal gas. Ways to change internal energy.

Quantity of heat. Work in thermodynamics

Internal energy is the sum of the kinetic energy of the chaotic motion of molecules and the potential energy of their interaction.

Since the molecules of an ideal gas do not interact with each other, the internal energy U of an ideal gas is equal to the sum of the kinetic energies of randomly moving molecules:
, where .
In this way,

,
where .

For a monatomic gas i = 3, for diatomic i = 5, for three (or more) atoms i = 6.

Change in the internal energy of an ideal gas
.
The internal energy of an ideal gas is a function of its state. Internal energy can be changed in two ways:

by heat exchange;
by doing work.

The process of changing the internal energy of a system without performing mechanical work is called heat exchange or heat transfer. There are three types of heat transfer: conduction, convection and radiation.

^ The amount of heat called the value, which is a quantitative measure of the change in the internal energy of the body in the process of heat transfer.

The amount of heat required for heating (or given off by the body during cooling) is determined by the formula:
where c is the specific heat capacity of the substance
Work in thermodynamics

elementary work d A = p dV. At p = const
^ 16. System status. Process. First law (first law) of thermodynamics
body system called the set of considered bodies. An example of a system would be a liquid and a vapor in equilibrium with it. In particular, the system may consist of one body.

Any system can be in different states, differing in temperature, pressure, volume, etc. The quantities characterizing the state of the system are called state parameters.

Not always any system parameter has a certain value. If, for example, the temperature in different points body is not the same, then the body cannot be assigned a specific temperature value. In this case, the state of the system is called nonequilibrium.

equilibrium the state of the system is such a state in which all the parameters of the system have certain values that remain constant under unchanged external conditions for an arbitrarily long time.

process called the transition of a system from one state to another.

Internal energy is a function of the state of the system. This means that whenever a system finds itself in a given state, its internal energy assumes the value inherent in this state, regardless of the system's history. The change in the internal energy of the system during its transition from one state to another (regardless of the path along which the transition is made) is equal to the difference in the values of the internal energy in these states.

According to the first law of thermodynamics the amount of heat communicated to the system goes to increase the internal energy of the system and to make the system work on external bodies.

Application of the first law of thermodynamics to processes in gases. adiabatic process.

Isothermal process (T=const)

Because .
Gas work in an isothermal process
.

Isochoric process (v=const)

Since Therefore

isobaric process (p=const)

adiabatic process (Q = 0).

A process is said to be adiabatic if there is no heat exchange with environment.

The adiabatic equation (Poisson equation) has the form .

According to the first law of thermodynamics Hence, .

With adiabatic expansion, therefore (the gas is cooled).

Under adiabatic compression, therefore (the gas heats up). Adiabatic air compression is used to ignite fuel in diesel internal combustion engines.
^ 17. Heat engines
A heat engine is a device that converts the energy of burned fuel into mechanical energy. A heat engine in which the working parts periodically return to their original position is called a periodic heat engine.

Heat engines include:

steam engines,
internal combustion engines (ICE),
jet engines,
steam and gas turbines,
refrigeration machines.

For the operation of a periodic heat engine, the following conditions must be met:

the presence of a working fluid (steam or gas), which, heating up during the combustion of fuel and expanding, is capable of performing mechanical work;
use of a circular process (cycle);
heater and refrigerator.

Second law of thermodynamics

The scheme of the heat engine has the form shown in the figure. the amount of heat received by the working fluid from the heater is the amount of heat given by the working fluid to the refrigerator.

It can be seen from the diagram that the heat engine does work only by transferring heat in one direction, namely from more heated bodies to less heated ones, and all the heat taken from the heater cannot be

Turned into mechanical work. This is not an accident, but the result of objective laws that exist in nature, which are reflected in the second law of thermodynamics. The second law of thermodynamics shows in which direction thermodynamic processes can proceed, and has several equivalent formulations. Specifically, Kelvin's formulation is: such a periodic process is impossible, the only result of which is the conversion of the heat received from the heater into work equivalent to it.

^ heat engine efficiency. Carnot cycle.

The coefficient of performance (COP) of a heat engine is a value equal to the ratio of the amount of heat converted by the engine into mechanical work to the amount of heat received from the heater:

^ The efficiency of a heat engine is always less than unity.

To determine the maximum possible value of the efficiency of a heat engine, the French engineer S. Carnot calculated an ideal reversible cycle consisting of two isotherms and two adiabats. He proved that the maximum value of the efficiency of an ideal heat engine operating without losses on a reversible cycle
.
Any real heat engine operating with a heater at temperature and a cooler at temperature cannot have an efficiency higher than that of an ideal heat engine at the same temperatures.
ELECTROMAGNETISM
^ 1. Electrification of bodies. The law of conservation of electric charge. Coulomb's Law
Many particles and bodies are able to interact with each other with forces that, like the forces of gravity, are proportional to the square of the distance between them, but many times greater than the forces of gravity. This type of particle interaction is called electromagnetic.

^ Therefore, electric charge is a quantitative measure of the ability of particles to electromagnetic interactions.

There are two types of electric charge, conditionally called positive and negative. Like charges repel, and unlike charges attract.

It has been experimentally established that the charge of any body consists of an integer number of elementary charges, i.e. electric charge is discrete. The elementary charge is usually denoted by the letter e. charge of all elementary particles(if it is not equal to zero) is the same in absolute value.
|e| = 1.6 10 -19 C
Any charge greater than an elementary charge consists of an integer number of elementary charges
q = ± Ne (N = 1, 2, 3, …)
The electrification of bodies always comes down to the redistribution of electrons. If the body has an excess of electrons, then it is negatively charged; if there is a shortage of electrons, then the body is positively charged.

^ In an isolated system, the algebraic sum of electric charges remains constant (the law of conservation of electric charge):
q 1 + q 2 +…+ q N = ∑q i = const
The law to which the force of interaction of point fixed charges obeys was established by Coulomb (1785)

A point charge is a charged body, the dimensions of which can be neglected in comparison with the distances from this body to other bodies that carry an electric charge.

According to Coulomb's law, the force of interaction of two motionless point charges in vacuum is directly proportional to the product of charge modules and inversely proportional to the square of the distance between them.

k is the coefficient of proportionality.

In SI k =	1
	4πε 0

k \u003d 9 10 9 N m 2 / C 2 ε 0 \u003d 8.85 10 -12 C 2 / N m 2 (ε 0 is the electrical constant).

^ 2. Electric field. tension electric field. The principle of superposition of electric fields
An electric field is a type of matter through which the interaction of electric charges occurs.

The power characteristic of the electric field is the strength of the electric field.

The strength of the electric field at a given point is equal to the ratio of the force with which the field acts on a test charge placed in given point field, to the magnitude of this charge.
.
The electric field strength is measured in or in.

Field strength point charge.

According to the principle of superposition (superposition) of fields, the field strength of a system of charges is equal to the vector sum of the field strengths that each of the charges of the system would create separately.

+ q 1 - q 2

Electric fields can be depicted graphically using lines of tension (lines of force) of the electric field.

An electric field strength line is a line, the tangent to which at each point coincides with the direction of the strength vector at that point.

^ 3. The work of the forces of the electrostatic field. Electrostatic field potential

F
dr α dl
1 q ´ 2

r 1 r 2

The force acting on a point charge in the field of another charge is central. The central field of forces is potential. If the field is potential, then the work to move the charge in this field does not depend on the path along which the charge movesa depends on the initial and final position of the charge and .

Work on the elementary path

= .
From this formula it follows that the forces acting on the charge in the field of a fixed charge are conservative, because the work done to move the charge is really determined by the initial and final position of the charge.

From the course of mechanics it is known that the work of conservative forces on a closed path is zero.

^ The circulation of the electrostatic field intensity vector along any closed loop is equal to zero.

Potential

A body in a potential field of forces has energy, due to which work is done by the forces of the field
.
Therefore, the potential energy of the charge in the field of a fixed charge
.
The value equal to the ratio of the potential energy of the charge to the value of this charge is called the potential of the electrostatic field
.
Potential is an energy characteristic of an electric field.

Electric field potential of a point charge
.
The potential of the field created by a system of charged bodies is equal to the algebraic sum of the potentials created by each charge separately
.
The charge located at the point of the field with the potential has the energy
.
The work of the field forces on the charge

The quantity is called voltage. Potential and potential difference (voltage) are measured in volts (V).
^ 4. Relationship between the strength of the electrostatic field and the potential
The work of the forces of the electric field on the charge on the segment of the path
.

On the other hand, therefore.

Hence it follows that
. ; ; .

.
The value in brackets is called the potential gradient.

Therefore, the electric field strength is equal to the potential gradient, taken with the opposite sign.

For a uniform electrostatic field , at the same time . Hence, , .

For a visual representation of the electric field, along with lines of tension, surfaces of equal potential (equipotential surfaces) are used. The electrostatic field strength lines are perpendicular (orthogonal) to the equipotential surfaces.
^ 5. Conductors in an electrostatic field. The phenomenon of electrostatic induction. Dielectrics in an electrostatic field
Conductors in an electrostatic field. electrostatic induction.

Conductors include substances that have free charged particles that can move in an orderly manner throughout the entire volume of the body under the influence of an electric field. The charges of such particles are called free.

Metals are conductors, some chemical compounds, aqueous solutions salts, acids and alkalis, molten salts, ionized gases.

Consider the behavior of solid metal conductors in an electric field. In metals, the carriers of free charges are free electrons, called conduction electrons.

+σ E 0 -σ
- +

If an uncharged metal conductor is introduced into a uniform electric field, then under the action of the field in the conductor, a directed movement of free electrons occurs in the direction opposite to the direction of the intensity vector E O this field. Electrons will accumulate on one side of the conductor, forming an excess negative charge there, and their shortage on the other side of the conductor will lead to the formation of an excess positive charge there, i.e. charge separation occurs in the conductor. These uncompensated opposite charges appear on the conductor only under the action of an external electric field, i.e. such charges are induced (induced), and in general the conductor still remains uncharged.

This type of electrization, in which, under the action of an external electric field, the redistribution of charges between parts of a given body occurs, is called electrostatic induction.

The uncompensated electric charges that appeared as a result of electrostatic induction on opposite parts of the conductor create their own electric field, its intensity E With inside the conductor is directed against tension E O external field in which the conductor is placed. As the charges separate in the conductor and accumulate on opposite parts of the conductor, the tension E With internal field increases and becomes equal to E O. This leads to tension E the resulting field inside the conductor becomes zero. In this case, an equilibrium of charges on the conductor occurs.

The entire uncompensated charge in this case is only on the outer surface of the conductor, and there is no electric field inside the conductor.

This phenomenon is used to create electrostatic protection, the essence of which is that in order to protect sensitive devices from the influence of electric fields, they are placed in grounded metal cases or grids.

^ Dielectrics in an electrostatic field.

Dielectrics are substances in which normal conditions(i.e. at not too high temperatures and the absence of strong electric fields) there are no free electric charges.

Unlike conductors in dielectrics, charged particles are not able to move throughout the entire volume of the body, but can only be displaced over small distances (on the order of atomic distances) relative to their constant positions. Therefore, the electric charges in dielectrics are related.

Depending on the structure of the molecules, all dielectrics can be divided into three groups. The first group includes dielectrics, the molecules of which have an asymmetric structure (water, alcohols, nitrobenzene). In such molecules, the centers of distribution of positive and negative charges do not coincide. Such molecules can be considered as electric dipoles.

Molecules that are electric dipoles are called polar. They have electric moment p= q l even in the absence of an external field.

The second group includes dielectrics whose molecules are symmetrical (for example, paraffin,

Absolute temperature zero corresponds to 273.15 degrees Celsius below zero, 459.67 below zero Fahrenheit. For the Kelvin temperature scale, this temperature itself is the zero mark.

The essence of absolute zero temperature

The concept of absolute zero comes from the very essence of temperature. Any body that gives up to the external environment in the course of . In this case, the body temperature decreases, i.e. there is less energy left. Theoretically, this process can continue until the amount of energy reaches such a minimum at which the body can no longer give it away.
A distant harbinger of such an idea can already be found in M.V. Lomonosov. The great Russian scientist explained heat by "rotary" motion. Therefore, the limiting degree of cooling is a complete stop of such movement.

According to modern concepts, the absolute zero temperature is at which molecules have the lowest possible energy level. With less energy, i.e. at a lower temperature, no physical body can exist.

Theory and practice

Absolute zero temperature is a theoretical concept, it is impossible to achieve it in practice, in principle, even in the conditions of scientific laboratories with the most sophisticated equipment. But scientists manage to cool the matter to very low temperatures, which are close to absolute zero.

At such temperatures, substances acquire amazing properties that they cannot have under ordinary circumstances. Mercury, which is called "living silver" because of its near-liquid state, at this temperature becomes solid - to the point that it can hammer nails. Some metals become brittle, like glass. The rubber becomes just as hard. If a rubber object is hit with a hammer at a temperature close to absolute zero, it will break like glass.

Interesting phenomena occur with metals. The atoms of the crystal lattice vibrate with a smaller amplitude, the scattering of electrons decreases, therefore, the electrical resistance decreases. The metal acquires superconductivity, the practical application of which seems very tempting, although difficult to achieve.

The term "temperature" appeared at a time when physicists thought that warm bodies consist of a larger amount of a specific substance - caloric - than the same bodies, but cold ones. 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 fact, 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 - the temperature of the mixture of water ice - ammonia and the other - 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, a former contemporary of Kelvin and one of the creators 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.