Every person daily comes across the concept of temperature. The term has firmly entered our daily lives: we heat food in the microwave or cook food in the oven, take an interest in the weather on the street or find out if the water in the river is cold - all this is closely connected with this concept. And what is temperature, what does this physical parameter mean, what is it measured in? We will answer these and other questions in the article.
Physical quantity
Let's look at what temperature is from the point of view of an isolated system in thermodynamic equilibrium. The term came 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 the isolated system is out of equilibrium, over time there is a transition of energy from more heated objects to less heated. The result is an equalization (change) in temperature throughout the system. This is the first postulate (zero beginning) of thermodynamics.
The temperature determines the distribution of the constituent particles of the system according to energy levels and speeds, the degree of ionization of substances, the properties of equilibrium electromagnetic radiation of bodies, and the total bulk density of radiation. Since for a system that is in thermodynamic equilibrium, the parameters listed 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 electron to electron and from ion to ion. But between the heterogeneous elements there is a slow transition. Plasma can be in a state in which electrons and ions are individually close to equilibrium. In this case, individual temperatures of each type of particle can be taken. 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 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 both positive and negative. 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. In an opposite situation, this process will proceed in the opposite direction - a negative temperature will be "above" positive.
Why is this necessary?
The paradox is that the average person does not even need to know what temperature is in order to conduct the measurement process both in everyday life and in industry. 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 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 converted to the desired value.
It turns out to determine the temperature, there is no need to study physics. By this principle, a large part of the population of our planet lives. If the TV is working, then there is no need to understand the transient processes of semiconductor devices, to study where the electricity comes from the outlet or how the signal arrives on the satellite dish . People are accustomed to the fact that in each area there are specialists who can fix or debug the system. The average person does not want to strain his brain, because it is much better to watch a soap opera or football on the “box” while sipping cold beer.
I want to know
But there are people, most often these are students who, either to the extent of their curiosity, or, if necessary, are forced 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, an inquiring mind will have to comprehend Carnot cycles and entropy. And at the end of his journey, he will surely recognize that determining the 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 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 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 body temperature. So, particles of a heated system move faster than cold ones.
Since the term in question is closely related to the averaged kinetic energy of a group of particles, it would be natural to use the joule as a unit of temperature. Nevertheless, this does not happen, which is explained by the fact that the energy of the thermal motion of elementary particles is very small with respect to the joule. Therefore, its use is inconvenient. Thermal movement is measured in units obtained from joules by means of a special conversion factor.
Temperature Units
To date, three basic units are used to display this parameter. In our country, the temperature is usually determined in degrees Celsius. The basis of this unit is the solidification point of water - the absolute value. She is the origin. 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 conditional value was taken for convenience. The second absolute value is the temperature of the steam, that is, the moment when water from a liquid state passes into a gaseous state.
The next unit is Kelvin degrees. 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 reference point. We get that zero according to 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 temperature unit with “Kelvin”.
The third common unit of measure is degrees Fahrenheit. Until 1960, they were widely used in all English-speaking countries. However, today in the home in the United States use this unit. The system is fundamentally different from those described above. The reference point is the freezing temperature of a mixture of salt, 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 boiling - plus 212 degrees. In this system, one degree is 1/180 of the difference in these temperatures. So, the range from 0 to +100 degrees Fahrenheit corresponds to the range from -18 to +38 degrees Celsius.
Absolute zero temperature
Let's see what this parameter means. Absolute zero is the value of the limiting temperature at which the ideal gas pressure 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." The Avogadro chemical law follows from this : equal volumes of gases under the condition of the same temperature and pressure contain the same number of molecules. What follows from this? There is a minimum gas temperature at which its pressure or volume will vanish. 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 heating. So, the temperature of the core of our earth is about the same as on the surface of the sun. The hottest planet is considered to be Jupiter. The temperature in the center of its core is five times higher than on the surface of the Sun. But the lowest value of the parameter was recorded on the surface of the moon - it amounted to only 30 kelvin. 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 Brookhaven New York 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 opposite is true. 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.