Two simple problems in thermals, several problems in thermals

1. The essence of the error is that the mechanical energy of an object is macroscopic energy, and the kinetic energy and potential energy of a cannonball refer to the macroscopic energy of its motion and height relative to the ground, which is generally used to study macroscopic physical phenomena. The concept of kinetic energy and potential energy of molecules is used to study the microscopic world, and is generally not measured by its motion and height (the particles in the microstructure) relative to the ground, that is, the kinetic energy and potential energy of molecules refers to the energy determined by the microscopic motion and the microscopic position of the molecule, which has nothing to do with the motion and height of the whole object, and their kinetic energy refers to the kinetic energy due to its irregular thermal motion, and its irregularity is significantly different from the consistency of the direction of macroscopic motion and the relative stability of velocity. Their potential energy refers to the energy they have due to the gravitational pull between molecules and the relative distance between molecules, regardless of the height of the whole object. This distinction is important for future studies of thermal science and must be noted.

Otherwise, it is impossible to correctly understand the important concept of "entropy" derived from the second law of heat. ）

2. It is the transformation between different forms of energy and the transfer of the same form of energy, one is the conversion of work into heat, and the other is the transfer of heat. The irreversibility of the conversion of work into heat is manifested in the fact that work can be completely converted into heat, while heat into work must be lost, that is, heat cannot be completely converted into work. And the irreversibility of heat transfer is manifested in the fact that it can only have a high temperature object to a low temperature object.

1。Mistake. Because the internal energy of the molecule is the embodiment of the microscopic thermal motion of the molecule, it has nothing to do with the macroscopic kinetic energy internal energy. Therefore, this statement is wrong.

2.Work is the conversion of part of the internal energy of an object into mechanical energy, whereas heat transfer is the exchange of heat, which is the transfer of heat from a high-temperature object to a low-temperature object to change the internal energy.

Incorrect molecular kinetic energy refers to the presence of temperature.

Molecular potential energy refers to the forceful interaction between molecules.

2 Heat transfer is the transfer of energy Work done is the transformation of energy.

OK. According to the first law of thermodynamics, the increase in internal energy u = external workmanship w + heat absorption q.

When the heat q is absorbed and the system does not do work on the outside world, the internal energy increases (for example, the isochoric heating of the gas, all the heat is converted into internal energy);

If the absorbed heat q is used to do work on the external body (such as the isothermal change of the gas, we know that the internal energy is a large physical quantity that depends only on the temperature), then the internal energy does not increase.

The physical meaning of 2 2 kt and 2 3rt can be understood as the energy of a two-dimensional system and a three-dimensional system respectively (the energy equalization theorem: each degree of freedom of the system contributes 1 2kt to energy).

The specific mathematical process is more complicated. A lot of knowledge of statistical physics is required.

1. There is a distribution function called Gaussian distribution in mathematics, and there are many things that satisfy the Gaussian distribution. The physical Maxwell distribution is a Gaussian distribution.

2. As long as the function of temperature to the measured quantity is monographic.

3. The transport phenomenon disappears after the system reaches equilibrium. When the system reaches equilibrium, the macro-state does not change with time, but the macro-state does not change with time, and the system does not necessarily reach equilibrium.

1.The internal energy is determined by both the potential energy and the kinetic energy of the molecule, and when the volume is constant, the internal energy is determined by the temperature, and when the ice becomes water, the temperature of the ice-water mixture does not change to 0 degrees, but the internal energy keeps increasing2If it's a solid, if it's a gas, it's wrong, because the temperature drops, it's probably because the volume of the gas decreases, and the work is done externally.

False: When the water turns into ice, the exothermic temperature is 0

3.The solid may work on the gas externally, so that the volume expands, the temperature may increase, decrease or remain unchanged, and the error may be to do work on the object, for example, when the iron block is smashed with a hammer, the temperature of the iron block will increase4Solid vs. gas is wrong because the molecular potential energy of the gas may increase, and the magnitude of the internal energy cannot be determined, and the solid vs. gas may have a decrease in molecular potential energy while the temperature does not change.

It seems to be a junior high school topic, and high school generally discusses gases and ideal gases, and solids with constant volume are not considered as test topics because they are simple, but at the high school level, all of the above questions are wrong, because the internal energy of an object is determined by both the potential energy of the molecule and the kinetic energy of the molecule, and even solids have potential energy changes, so heat becomes very troublesome.

But there are a lot of restrictions in junior high school and high school, so it's easy to learn hotly, but it's these constraints that make some problems contradictory, and many students don't understand, because the knowledge of junior high school and high school is just some of the most basic theories, and a chapter of hot learning in high school is a book in college, so those places that you don't understand may be more in-depth, but the teacher doesn't tell you, and I don't do research in middle school.

There is no need to cite so many examples.

I have research on this piece.

You can ask me online.

The heat flux in a small area is proportional to the temperature difference. To put it simply, the time between two local high temperature differences is fast heat exchange rate, and the low temperature difference between local heat exchange speed is slow, and the two are proportional. As the temperature of the gas is continuously distributed, this equation is strictly a differential equation and is not necessary to contain a high altitude.

With the temperature is actually a continuous distribution, so the actual wording of this formula is dq = hdt

The definition of magnetic flux, in practice, is to define a vector and sensitive measurement field (which is the temperature gradient, in-depth to use some mathematical expressions) and to define the normal direction of a surface, an inseparable component, through which the flux passes. Here it can be understood as the amount of heat flux that is represented.

Rigorous derivation is found in the derivation of the above heat conduction equation (provided that you must be on an appropriate mathematical basis) to find mathematically.

Kinetics provides a process of how to grow into this material, a possibility of actual growth, is a necessary condition, summarizes the fundamental law of thermal phenomena, and only then can this material exist, and this result, experiment, and analysis of thermodynamics is a macroscopic theory of thermal motion.

Dynamics is a sub-discipline of theoretical mechanics that studies the relationship between the forces acting on an object and its motion.

For the study of materials, thermodynamics provides a possible result, that is, it must be in accordance with thermodynamics. These experimental laws are the culmination of countless experiences and are applicable to all macroscopic systems. The conclusions of thermodynamics, like the laws on which they are based, are universal and reliable.

However, thermodynamics also has definite limitations, mainly in that it cannot reveal the basic laws of thermodynamics and the microscopic nature of its conclusions, and cannot explain the fluctuation phenomenon. Through the observation of thermal phenomena. For example, the study of the growth of semiconductor nanodots.

1. The commonly used liquids in the capillary glass tube of thermometers commonly used in homes and laboratories are: mercury, kerosene, and alcohol. Of course, other organic solvents, such as acetone, methanol, benzene, ether, glycerol, etc., can also be used as thermometer liquids.

2. Normally, mercury is not stained, that is, the color of mercury itself (metallic silver) is used; Kerosene, alcohol, etc., are dyed red, and the purpose is to be eye-catching and convenient to observe.

3. It is often used as a thermometer liquid column liquid to meet the conditions

a.Sensitivity to heat (i.e., good characteristics of thermal expansion and contraction);

b.The melting and boiling points span a large one;

c.Glass tubing does not infiltrate wetting liquids.

4. There are three kinds of commonly used liquids: mercury (-39 357) alcohol (-117 78) kerosene (generally -30 150) Therefore, according to the different melting and boiling point ranges of the three liquids, mercury thermometer, alcohol thermometer and kerosene thermometer are suitable for occasions with different temperature measurement ranges.

According to the difference in the characteristics of thermal expansion and cold contraction of the three liquids, the three thermometers are suitable for occasions with different temperature measurement accuracy requirements.

The alcohol thermometer can measure low temperatures because it has a freezing point of -117, which can be used even in Antarctica, the hottest city on Earth (the lowest temperature on the Earth's surface). Mercury is different, it solidifies at -39. After the mercury solidifies, it loses its fluidity, and even if the surrounding temperature continues to drop, the mercury can no longer indicate the temperature.

In some places in the northeast of our country, the temperature in winter is often -40, so it is only suitable to use alcohol thermometers in these colder places.

However, alcohol also has the great disadvantage that it takes much more calories than mercury to raise the temperature of the same weight of alcohol and mercury1. The amount of heat that raises (or decreases)1 alcohol can raise (or decrease) mercury by about 20. For the same temperature changes, a mercury thermometer is much more sensitive than an alcohol thermometer.

Therefore, mercury thermometers are generally used in scientific experiments or when measuring human body temperature. Another advantage of a mercury thermometer is that it can be used to measure high temperatures, as it has a boiling point of up to 357.

Of course, there is another disadvantage of mercury thermometers: during use, once the thermometer is accidentally broken, the mercury inside leaks, and the liquid mercury will volatilize into the air and cause harm to the human body.

I hope it helps you, and if you have any questions, you can ask them

I wish you progress in your studies and go to the next level! (*

This is usually the three liquids.

It's not clear if you dye it, do you talk about physics = =

The laboratory generally uses a kerosene thermometer The thermometer is mercury Alcohol is generally measured at a very low temperature, especially if the thermometer has a neck, it should be thrown down before use, you can leave the object to read, I just finished the high school exam, if you have any questions, ask me.

Heat is not the focus, the thermometer test is at most one reading, and then there is a calculation question to calculate the specific heat capacity, it is recommended to focus on mechanics and electricity

These are common, and you can only see these three types in junior high school.

The mercury in the thermometer is red. The thermometer that the teacher brought that day was also red.

Because each of them has its own characteristics.

Alcohol thermometers have a low freezing point, so they are suitable for cold regions, and mercury thermometers are suitable for body temperature types. Kerosene, I haven't encountered it yet.