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What is the temperature? Temperature units are degrees. Steam and gas temperature

Every person faces the notion of temperature on a daily basis. The term has firmly entered our everyday life: we are heating up food in the microwave oven, preparing food in the oven, being interested in the weather on the street or finding out whether the water is cold in the river - all of which is closely related to this concept. And what is the temperature, what does this physical parameter mean, in what is it measured? These and other questions will be answered in the article.

Physical quantity

Let's consider what temperature is from the standpoint of an isolated system in thermodynamic equilibrium. The term came from Latin and means "proper mixing," "normal state," "proportionality." This quantity characterizes the state of thermodynamic equilibrium of any macroscopic system. In the case when the isolated system is out of balance, energy passes from more heated objects to less heated over time. The result is a temperature equalization (change) in the whole system. This is the first postulate (zero-point) of thermodynamics.

Temperature determines the distribution of the constituent particles of the system in terms of energy levels and velocities, the degree of ionization of substances, the properties of equilibrium electromagnetic radiation of bodies, the total volume density of radiation. Since for the system that is in thermodynamic equilibrium, the listed parameters are equal, they are usually called the temperature of the system.

Plasma

In addition to equilibrium bodies, there are systems in which the state is characterized by several temperature values that are not equal to each other. A good example is plasma. It consists of electrons (light charged particles) and ions (heavy charged particles). In their collisions, there is a rapid transfer of energy from the electron to the electron and from the ion to the ion. But between the heterogeneous elements there is a slow transition. The plasma can be in a state in which the electrons and ions are individually close to equilibrium. In this case, it is possible to take the individual temperatures of each kind of particles. However, these parameters will differ among themselves.

Magnets

In bodies in which particles have a magnetic moment, energy transfer usually occurs slowly: from translational to magnetic degrees of freedom, which are associated with the possibility of changing the direction of the moment. It turns out that there are states in which the body is characterized by a temperature that does not coincide with the kinetic parameter. It corresponds to the translational motion of elementary particles. The magnetic temperature determines part of the internal energy. It can be either positive or negative. In the process of equalization, energy will be transferred from particles with a larger value to particles with a lower temperature value if they are both positive or negative. In a nasty situation, this process will proceed in the opposite direction - the negative temperature will be "higher" than the positive one.

And why is this necessary?

The paradox is that the average person, in order to carry out the measurement process both in everyday life and in industry, does not even need to know what temperature is. It will be sufficient for him to understand that this is the degree of heating of an object or medium, especially since we are familiar with these terms from childhood. Indeed, most practical instruments designed to measure this parameter actually measure other properties of substances that vary from the level of heating or cooling. For example, pressure, electrical resistance, volume, etc. Further, such readings are manually or automatically recalculated to the desired value.

It turns out to determine the temperature, there is no need to study physics. By this principle, most of the population of our planet lives. If the TV is working, there is no need to understand the transient processes of semiconductor devices, to study where the electricity comes from in the outlet or how the signal goes to the satellite dish . People are used to the fact that in every area there are specialists who can repair or debug the system. The philistine does not want to strain his brain, because it's much better to watch soap opera or football on the "box", sipping cold beer.

And I want to know

But there are people, most often they are students who, either in the measure of their curiosity, or necessarily have to study physics and determine what the temperature really is. As a result, in their search, they fall into the jungle of thermodynamics and study its zero, first and second laws. In addition, the curious mind will have to comprehend Carnot cycles and entropy. And at the end of his journey he certainly recognizes that the definition of temperature as a parameter of a reversible thermal system that does not depend on the type of working substance will not add clarity to the sense of this concept. Still, the visible part will be some degrees accepted by the international system of units (SI).

Temperature as kinetic energy

More "tangible" is the approach, which is called molecular-kinetic theory. From it a representation is formed that heat is considered as one of the forms of energy. For example, the kinetic energy of molecules and atoms, a parameter averaged over a huge number of chaotically moving particles, turns out to be a measure of what is commonly called the body temperature. Thus, the particles of the heated system move faster than the cold ones.

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

Temperature units

To date, there are three basic units for displaying this parameter. In our country, the temperature is usually determined in degrees Celsius. At the heart of this unit of measurement lies the point of solidification of water - the absolute value. It is the origin. That is, the temperature of the water at which ice starts to form is zero. In this case, water serves as a model yardstick. This conditional value was taken for convenience. The second absolute value is the temperature of the steam, that is, the time when water from the liquid state passes into the gaseous state.

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

The third common unit of measurement is degrees Fahrenheit. Until 1960, they were widely used in all English-speaking countries. However, even today in everyday life in the United States use this unit. The system is fundamentally different from the ones described above. For the reference point, the freezing temperature of a mixture of salt, ammonia and water in a ratio of 1: 1: 1 is adopted. So, on the Fahrenheit scale, the freezing point of water is plus 32 degrees, and boiling - plus 212 degrees. In this system, one degree is 1/180 of the difference of these temperatures. So, the range from 0 to +100 degrees Fahrenheit corresponds to a range from -18 to +38 Celsius.

Absolute zero temperature

Let's see what this option means. An absolute zero is the value of the limiting temperature at which the ideal gas pressure vanishes for a fixed volume. This is the lowest value in nature. As Mikhailo Lomonosov predicted, "this is the greatest or the last degree of cold." This follows the Avogadro's chemical law: in equal volumes of gases, under the condition of the same temperature and pressure, the same number of molecules are contained. What follows from this? There is a minimum gas temperature at which its pressure or volume will vanish. This absolute value corresponds to zero according to Kelvin, or 273 degrees Celsius.

Some interesting facts about the solar system

The temperature on the surface of the sun reaches 5700 Kelvin, and in the center of the nucleus - 15 million Kelvin. The planets of the solar system are very different from each other in terms of the level of heating. Thus, the core temperature of our Earth is about the same as on the surface of the Sun. The most hot planet is Jupiter. The temperature at the center of its core is five times higher than on the surface of the Sun. But the lowest value of the parameter was fixed on the surface of the Moon - it was only 30 Kelvin. This value is even lower than on the surface of Pluto.

Facts about the Earth

1. The highest temperature that a person recorded was 4 billion degrees Celsius. This value is 250 times higher than the temperature of the Sun's core. Record set by the New York Natural Laboratory of Brookhaven in the ion collider, whose length is about 4 kilometers.

2. The temperature on our planet is also not always ideal and comfortable. For example, in the city of Verkhnoyansk in Yakutia, the temperature in winter falls to minus 45 degrees Celsius. But in the Ethiopian city of Dallall the opposite situation. There, the average annual temperature is plus 34 degrees.

3. The most extreme conditions under which people work are recorded in the gold mines in South Africa. Miners work at a depth of three kilometers at a temperature of plus 65 degrees Celsius.

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