Shulou(Shulou.com)11/24 Report--

We've all seen high voltage towers, right?

Although it was designed

It is very thoughtful in terms of safety.

But don't do it around here.

Q1 Why does the liquefaction and sublimation of water vapor need condensation nuclei? By Anonymous

A:

This question seems to be a careful reading of the previous question No. 328 on the "aircraft cable" question 😎 (do fluorescent lamps tan people? What kind of light can bask in black people? | No.328). First of all, it is stated that in period 328, the condensed nodule refers to the aerosol particles in the atmosphere, which can make the water vapor molecules in the upper atmosphere liquefy and sublimate with them as the center. It does not mean that the liquefaction and sublimation of water vapor must have the presence of condensed nodules (especially such aerosols). (changing temperature and pressure is the most direct way to cause phase transition. in addition, the principle of homogeneous nucleation can also cause spontaneous nucleation and phase transition of matter.)

So, why can water vapor liquefy and sublimate under the action of condensed nodules? This is because in the upper atmosphere, due to the existence of low temperature and low pressure environment, it is usually in the area rich in water vapor, in which the environmental water vapor content exceeds the water vapor content in the saturated state, thus forming supersaturated steam. Supersaturated steam is easy to liquefy or sublimate (i.e. undergo phase transition) in the presence of condensation nodules, which can be compared with the crystallization of supersaturated solution below.

For example, the supersaturated sodium acetate solution is prepared and anhydrous sodium acetate is dipped into the supersaturated solution with a glass rod. It can be seen that the supersaturated solution immediately forms a crystal nucleus with the glass rod as the center and undergoes phase transformation, thus turning into sodium acetate crystal. This is because the solubility of solute in supersaturated solution is much larger than that in saturated solution under the same external conditions. At this time, the supersaturated solution is in unstable equilibrium, and its stable state is rapidly destroyed by the external disturbance of the crystal nucleus, thus the phase transition begins.

Supersaturated sodium acetate solution undergoes phase transition in the presence of crystalline nuclei. [1] now return to the effect of condensed nuclei on water vapor described above. The aerosol in the atmosphere (usually between a few microns and dozens of microns in diameter) seems to be a disturbing impurity in this mass of supersaturated vapor, which first causes the phase transformation of the supersaturated vapor around it. Local density fluctuations are formed. Since then, these first batch of phase transition water molecules affect the supersaturated steam around them, resulting in the continuous diffusion of the phase transition process, thus forming the phenomenon of liquefaction and sublimation centered on the condensation nucleus.

Reference:

[1] supersaturated solution can be crystallized by light contact-watermelon video

[2] condensation nucleus | meteorology | Britannica

By Callo

Can Q2 glass be made into wires? By Anonymous

A:

Generally speaking, glass is an amorphous inorganic non-metallic material. For the electrical transport of conventional voltage and frequency, this kind of material is basically a mixture of various ionic compounds, in which there are neither itinerant electrons nor charged particles that can be transferred. It can be imagined that the electrical conductivity of this kind of material is very poor, basically it can be said to be "almost non-conductive", this thing is really not suitable to be a conductor.

But! You can't speak so absolutely. From the point of view of conductivity, if the surface of the glass is coated, it is still possible for the glass to conduct electricity, such as ITO glass. From the point of view of "making" the wire, although glass cannot be a conductor, it can be used as the insulator that wraps the wire. Of course, this is "yes but not necessary", because we have rubber. This kind of high-strength heat-resistant insulating material which can bend and stretch.

In addition, we can even extend the definition of wire slightly, if we think that wire is heat transfer, current transmission or electromagnetic wave. Well, if our wire runs in a higher frequency electromagnetic field instead of household appliances. For example, visible light. Then fiberglass really has a chance to show its talents.

By Luna

Q3 Why is it that some people's sweat is smelly, while others' sweat is tasteless or even fragrant? By, I don't know.

A:

To answer this question, we need to know the composition of sweat. 98% of the sweat is water, and the rest is mainly composed of sodium chloride, as well as a small amount of urea, lactic acid, ammonia, lipids and other salts (magnesium salt, iron salt, etc.). Most of the substances themselves are tasteless (in addition, although ammonia in sweat itself has flavor, it is not a determinant of sweat smell because its concentration is very low in most people's sweat).

The reason for the "sweat smell" is that the bacteria on the surface of the skin decompose the lipids in the sweat into "tasteful" small molecules of organic matter. When the concentration of these substances is appropriate, they constitute a person's body odor, and because each person's skin has different kinds of bacteria, everyone's body odor is also different. But when the concentration of these substances is high, they produce an unpleasant stench. Therefore, when someone excrets a high content of lipids in sweat, or does not clean up after sweating a lot, the bacteria on the surface of the skin metabolize a large number of lipids and proteins in sweat, which smells "smelly".

To sum up, whether the sweat produced by people has a taste and what kind of taste mainly depends on three points: the amount of sweat they secrete, the type of bacteria on the surface of the skin, and their own metabolic ability.

Reference:

[1] sweat-Wikipedia

By hibernating enthusiasts

Q4 at standard atmospheric pressure, does amorphous have a fixed boiling point? By is quiet.

A:

Amorphous crystals do not have a fixed melting point, which is even used as a basis for distinguishing crystals from amorphous crystals in junior and senior high school textbooks, but how should we understand this phenomenon from a microscopic point of view? In terms of microscopic composition, the atoms in the crystal form a neat arrangement (crystallization), and the surrounding environment of each atom is the same. The arrangement of atoms in the corresponding amorphous crystal is relatively chaotic, and the surrounding environment of each atom may be different. If the crystal is heated up, when it reaches a certain temperature, the atoms in the crystal will consistently break free from the shackles of the surrounding environment (become liquid). From a microscopic point of view, some of the microscopic particles in the amorphous will break free while others do not. With the increase of temperature, amorphous crystals will lose the properties of solid and show the properties of liquid. And eventually become a liquid.

A typical example is glass in a molten state. In the process of blowing, glass can be pulled, bent and twisted, which is obviously not the property of a solid, but it is not like a fluid that cannot be formed. This is the property of an amorphous in a molten state.

Reference:

Folk craftsmen blow exquisite handmade glass in the fire

By Luna

Are people with long Q5 feet more likely to be electrocuted by step voltage? By controllable nuclear fusion

A:

Let's start with the conclusion: what really defeats you is not naivety, but "no shoes".

First of all, what is the step voltage? We know that whether it is lightning or a high voltage tower, when it produces an electric shock to the ground, the energy will slowly dissipate on the ground (not instantly disappear in the earth, lightning lasts for about 1 second to a few seconds, and the worst case of high voltage TV grounding is continuous discharge), while people who unfortunately walk in the surrounding potential distribution area form a path between their feet and the earth, and the voltage between them forms a step voltage (Step Voltage). The closer to the location of the electricity inflow, the higher the step potential. In addition, the soil itself has a resistance value, resulting in different potential differences at different distances. The greater the step, the greater the voltage difference between the feet.

In addition, according to the standards issued by the China Safety Association, 8-10 Ma AC, 50 Ma DC current or 40 V voltage is the maximum range for the average human body to withstand. Beyond this value, you will be injured by electric shock.

So unless your feet are unusual or you are descended from the Flash, it doesn't matter, so wear a pair of insulated shoes.

We might as well focus on what to do in case of a similar situation. A good practice should be to move slowly until you leave the charged area (it is hard to say how far away is the safe area, because the soil varies from place to place, and even the moisture content of the same piece of land may be different. When you can't move slowly with minimum steps, you can consider jumping on one foot or on both feet, but an accident may occur when you accidentally fall out of balance. By the way, we should also pay attention to avoid when working on an operating vehicle like the following, which may also have hidden risks.

To sum up, although the step voltage is dangerous, you can't be idle at ordinary times. The main inducements are: the size of the grounding current, the material of the shoes, the ground characteristics, the distance between the feet, and so on.

Finally, I hope you will never use this sharing.

Reference:

Yuan Xiaolei. Talking about step voltage electric shock [J]. Building Safety, 2004 (11): 23.

[2] step voltage-electrical career

[3] factors of human electric shock injury-China Association for production Safety

By 17

Q6 Why does the atmosphere have an ozone layer? Won't it be scattered in the atmosphere? By secondary account Yoda

A:

First of all, let's introduce what ozone is: ozone () is an important trace component of the natural atmosphere. After the oxygen molecules in the atmosphere are decomposed into oxygen atoms under the action of solar radiation, the oxygen atoms combine with the surrounding oxygen molecules to form. Therefore, it contains three oxygen atoms, which is a blue gas with a special smell at room temperature.

Fig. 1 Ozone introduction | the picture comes from [1] what is the ozone layer: the position of ozone stay is in the upper air of 15km from the ground, but the highest is not more than 50km, the air layer formed is called the ozone layer.

The specific reasons for the formation of the ozone layer can be summarized as follows: due to the continuous photolysis of water and the photosynthesis of plants, the concentration of oxygen increases gradually. Under the action of ultraviolet light, part of the oxygen can be converted into ozone. Because the volume of ozone is larger than that of oxygen, it slowly falls to the bottom of the ozone layer, but after a variety of environmental changes and photochemical reactions, ozone becomes unstable and becomes oxygen again. From the above reaction process, it can be seen that the dynamic balance between oxygen and ozone is maintained in the atmosphere, thus forming the ozone layer. Ozone accounts for only a very small part of the entire atmosphere, but it plays an important role in protecting human security.

Fig. 2 Ozone layer formation chart | the picture is derived from [2] the distribution of ozone in the atmosphere: ozone is usually distributed in two layers, the troposphere and the stratosphere. The thickness of the troposphere ranges from 10 km to 15 km above the ground, and the ozone in the troposphere is harmful to human beings and the ecological environment. The troposphere rises to about 50 km, commonly known as the stratosphere; the 15 km-50 km stratosphere preserves 90% of the ozone in the atmosphere, which mainly absorbs short-wave ultraviolet rays, forming a relatively stable ozone-rich atmosphere.

Figure 3 Ozone layer | the picture is from [1]

Fig. 4 Ozone layer | the picture is from [5] Resources:

[1] popular science of environmental protection? what is ozone and how is it distributed in the atmosphere?

[2] Ozone layer: the "umbrella" of life on Earth-China Science Popularization Network

[3] Ozone that people love and hate-Chinese Academy of Sciences

[4] the special design case of "Ozone layer destruction"-- the curriculum system of research-based learning in senior high school: environmental theme-- "Geography Teaching reference in Middle School" Z1, 2005.

[5] Why can the ozone layer protect the earth _ HD 1080p online viewing platform _ Tencent Video

By floor sweeping monk

Q7 Why can a spray can spray water into a fog? By, a curious man.

A:

Imagine that we hold the handle of the spray can, squeeze the spring of the sprinkler, and push the air into the small cavity, creating a rapid airflow. At this time, the air velocity of the nozzle is large, the pressure is small, and the pressure difference between the nozzle and the spray can is formed. According to Bernoulli's law, the water below will be pressed up by atmospheric pressure. In the case of a certain pressure, the smaller the area, the greater the pressure, and the nozzles of the spray pot are composed of many holes with very small area, so it is easy to get higher pressure when we use less force. So under the action of high pressure, the water is torn apart by the rapid air flow into very small droplets, which is foggy in terms of the resolution of our naked eye.

Reference:

[1] principle of spray can

By depth

Q8 Why can eggs become solid when heated? Or is it that boiled eggs are not solid? By Anonymous

A:

The process of turning an egg into a solid by heating is a process of protein denaturation by heat.

Fig. 1 raw eggs in colloidal state (left) and cooked eggs in solid solution (right)

First of all, cooked eggs are solid, but they contain protein, water and other substances, which are mixtures. The solid state often means that a pure substance is in a state of stable shape, and its shape does not adapt to the shape of the container, that is, it does not show fluidity. For mixtures, one of the components often exists as a solvent, while other substances are regarded as "soluble" in the solvent. For example, raw eggs are protein-based solid substances dissolved in water, so the whole is liquid, belonging to colloid. Cooked eggs are liquid water interspersed with a solid network of proteins, so it is more strictly a solid solution.

Fig. 2 Amino acid dehydration and condensation to form a peptide chain | the picture is from [1] so how is the protein denatured when heated? The first thing to do is to understand the composition of proteins. Various amino acids form peptide bonds by dehydration and condensation to form a long chain, which is called a peptide chain. The peptide chain is folded and bonded to have a three-dimensional structure. After folding, multiple peptide chains will be further combined and bonded to form proteins. Therefore, under normal circumstances, near-spherical proteins will dissolve in water in the form of particles to form colloids.

Fig. 3 Simulation of protein state before and after heating | the picture is from [1] but heating during cooking may destroy almost all bonds except peptide bonds, so granular proteins with three-dimensional structures will disintegrate the growth chain form. on the other hand, bonds may be formed between the long chains of multiple proteins, so that the whole will form a complex network. At this point, the water can only be dispersed into the gaps between these networks, unable to make the whole fluid.

Reference:

[1] Why Does an Egg Becomes Solid Upon Heating?

[2] solution-Wikipedia

By clouds open leaves and fall

What is the specific explanation of Q9BCS theory? By Anonymous

A:

One of the important properties of superconductors is zero resistance. According to the classical explanation, the source of resistance can be regarded as the collision (or scattering) between the electron and the atomic lattice, resulting in the transfer of part of the energy to the lattice, which is macroscopically represented by the current heating of the conductor.

Suppose that electrons in a vacuum are mutually exclusive. However, in the conductor, the interaction between the lattice and the electron can induce the attraction between the electrons, which can overcome the repulsion between the electrons and make the electrons pair in pairs at very low temperatures, which is called the C:Cooper in BCS. Electrons are fermions, but when paired into bosons, they are no longer limited by the Pauli incompatibility principle, which means that multiple Cooper pairs can be in the same quantum state, that is, condensation occurs.

At extremely low temperatures, Cooper pairs form Bose-Einstein condensates and protect electrons from the scattering of lost energy from the lattice. In other words, the generation of Cooper pairs makes the energy of the system lower, but more energy is needed to return to normal (that is, the energy gap is created). As long as the temperature does not reach enough energy for the lattice vibration to destroy the Cooper pair, the system cannot return from the superconducting state to the normal state, and the Cooper pair can keep the total momentum of the two electrons constant through mutual attraction, and the electrons will not lose energy due to scattering from the lattice. Of course, there is an upper limit for the superconducting current, and when the current is so large that the kinetic energy of the directional movement of electrons is enough to destroy the Cooper pair, the superconducting state will also be destroyed.

This is the microscopic image interpretation of zero resistivity by BCS theory. The theory was named after the initials BCS of the three authors, John Bardeen, Leon Cooper and John Shriver, for whom they were awarded the Nobel Prize in Physics in 1972.

By yellow water machine

This article comes from the official account of Wechat: Institute of Physics, Chinese Academy of Sciences (ID:cas-iop), author: Frions

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