Every person is faced with the concept of temperature every day. The term has firmly entered our daily life: we heat food in the microwave or cook food in the oven, we are interested in the weather outside or find out if the water in the river is cold - all this is closely related to this concept. And what is temperature, what does this physical parameter mean, in what way is it measured? We will answer these and other questions in the article.
Physical quantity
Let's consider what temperature is from the point of view of an isolated system in thermodynamic equilibrium. The term comes from the Latin language and means "proper mixing", "normal state", "proportionality". This value characterizes the state of thermodynamic equilibrium of any macroscopic system. In the case when an isolated system is out of equilibrium, over time there is a transition of energy from more heated objects to less heated ones. The result is an equalization (change) of temperature throughout the system. This is the first postulate (zero principle) of thermodynamics.
Temperature determinesdistribution of the constituent particles of the system by energy levels and velocities, the degree of ionization of substances, the properties of the equilibrium electromagnetic radiation of bodies, the total volumetric density of radiation. Since for a system that is in thermodynamic equilibrium, the listed parameters are equal, they are usually called the temperature of the system.
Plasma
Besides equilibrium bodies, there are systems in which the state is characterized by several temperature values that are not equal to each other. Plasma is a good example. It consists of electrons (light charged particles) and ions (heavy charged particles). When they collide, energy is rapidly transferred from electron to electron and from ion to ion. But between heterogeneous elements there is a slow transition. The plasma can be in a state in which the electrons and ions individually are close to equilibrium. In this case, separate temperatures for each kind of particles can be taken. However, these parameters will differ from each other.
Magnets
In bodies in which particles have a magnetic moment, energy transfer usually occurs slowly: from translational to magnetic degrees of freedom, which are associated with the possibility of changing the directions of the moment. It turns out that there are states in which the body is characterized by a temperature that does not coincide with the kinetic parameter. It corresponds to the translational motion of elementary particles. Magnetic temperature determines part of the internal energy. It can be either positive ornegative. During the alignment process, energy will be transferred from particles with a higher value to particles with a lower temperature value if they are both positive or negative. Otherwise, this process will proceed in the opposite direction - the negative temperature will be "higher" than the positive one.
Why is this necessary?
The paradox lies in the fact 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 environment, especially since we have been familiar with these terms since childhood. Indeed, most of the practical devices designed to measure this parameter actually measure other properties of substances that change with the level of heating or cooling. For example, pressure, electrical resistance, volume, etc. Further, such readings are manually or automatically converted to the desired value.
It turns out that to determine the temperature, there is no need to study physics. Most of the population of our planet lives by this principle. If the TV is on, then 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 arrives at the satellite dish. People are used to the fact that in every field there are specialists who can fix or debug the system. The layman does not want to strain his brain, because where is it better to watch a soap opera or football on the "box" while sippingcold beer.
I want to know
But there are people, most often students, who, either to the extent of their curiosity or out of necessity, are forced to study physics and determine what temperature really is. As a result, in their search, they fall into the wilds of thermodynamics and study its zero, first and second laws. In addition, an inquisitive mind will have to comprehend Carnot cycles and entropy. And at the end of his journey, he will surely admit that the definition of temperature as a parameter of a reversible thermal system, which does not depend on the type of working substance, will not add clarity to the feeling of this concept. And all the same, the visible part will be some degrees accepted by the international system of units (SI).
Temperature as kinetic energy
More "tangible" is the approach that is called molecular-kinetic theory. It forms the idea 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 randomly moving particles, turns out to be a measure of what is commonly called the temperature of a body. Thus, the particles of a heated system move faster than a cold one.
Since the term under consideration is closely related to the average kinetic energy of a group of particles, it would be quite natural to use the joule as a unit of temperature. However, this does not happen, which is explained by the fact that the energy of thermal motion of elementaryparticles is very small relative 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
Today, three basic units are used to display this parameter. In our country, the temperature is usually measured in degrees Celsius. This unit of measurement is based on the freezing point of water - an absolute value. She is the starting point. That is, the temperature of the water at which ice begins to form is zero. In this case, water serves as an exemplary measure. This convention has been adopted for convenience. The second absolute value is the steam temperature, that is, the moment when water changes from a liquid state to a gaseous state.
The next unit is Kelvin. The reference point of this system is considered to be the point of absolute zero. So, one degree Kelvin is equal to one degree Celsius. The difference is only the beginning of the countdown. We get that zero in 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 "degree Kelvin" for the unit of temperature with "kelvin".
The third common unit of measure is Fahrenheit. Until 1960, they were widely used in all English-speaking countries. However, today in everyday life in the United States use this unit. The system is fundamentally different from those described above. Taken as the starting pointfreezing point of a mixture of s alt, ammonia and water in a ratio of 1:1:1. So, on the Fahrenheit scale, the freezing point of water is plus 32 degrees, and the boiling point is plus 212 degrees. In this system, one degree is equal to 1/180 of the difference between these temperatures. So, the range from 0 to +100 degrees Fahrenheit corresponds to the range from -18 to +38 Celsius.
Absolute zero temperature
Let's understand what this parameter means. Absolute zero is the limiting temperature at which the pressure of an ideal gas vanishes at a fixed volume. This is the lowest value in nature. As Mikhailo Lomonosov predicted, "this is the greatest or last degree of cold." Avogadro's chemical law follows from this: equal volumes of gases at the same temperature and pressure contain the same number of molecules. What follows from this? There is a minimum temperature of a gas at which its pressure or volume vanishes. This absolute value corresponds to zero Kelvin, or 273 degrees Celsius.
Some interesting facts about the solar system
The temperature on the surface of the Sun reaches 5700 Kelvin, and in the center of the core - 15 million Kelvin. The planets of the solar system are very different from each other in terms of the level of heating. So, the temperature of the core of our Earth is about the same as on the surface of the Sun. Jupiter is considered the hottest planet. The temperature at the center of its core is five times higher than at the surface of the Sun. And here is the lowest value of the parameterrecorded on the surface of the moon - it was only 30 kelvins. This value is even lower than on the surface of Pluto.
Earth Facts
1. The highest temperature recorded by a person was 4 billion degrees Celsius. This value is 250 times higher than the temperature of the core of the Sun. The record was set by the New York Brookhaven Natural Laboratory in an ion collider, which is about 4 kilometers long.
2. The temperature on our planet is also not always ideal and comfortable. For example, in the city of Verkhnoyansk in Yakutia, the temperature in winter drops to minus 45 degrees Celsius. But in the Ethiopian city of Dallol, the situation is reversed. There, the average annual temperature is plus 34 degrees.
3. The most extreme conditions under which people work are recorded in gold mines in South Africa. Miners work at a depth of three kilometers at a temperature of plus 65 degrees Celsius.
