"Ahem, I asked you to read the question again, but I didn't hear it clearly just now," Li Mulin replied nonchalantly.
"A foreign junior high school student discovered a strange phenomenon. He put twice the same volume of milk into the refrigerator at the same time. One cup was 20 degrees Celsius and the other was 60 degrees Celsius. The result was surprising: the 60-degree cup of milk solidified first.
Bing. Please explain why!" Yang Niyan repeated the previous question in a stiff tone. After speaking, she glanced at Li Mulin and said, "Can you answer it? If you can't answer it, I will announce the examiner's score."
Li Mulin said with a faint smile on his face: "Actually, this question is very simple. Do you want to hear a simple answer or a complicated answer?"
"Of course you answered carefully!" Wang Kai said disdainfully.
"In fact, this phenomenon is called the Mpemba phenomenon in physics. From a physical perspective, there are four coexisting mechanisms of refrigeration: radiation, conduction, vaporization, and convection. Through experimental observation and comparison of the results, it was found that
The reason why hot water freezes before cold water is mainly due to the comprehensive effect of the interaction of conduction, vaporization and convection. A cup containing cold water with an initial temperature of 4℃ will take a long time to freeze because both water and glass are materials with poor thermal conductivity.
, it is difficult for the heat inside the liquid to be effectively transferred to the surface by conduction. As the temperature drops, the water in the cup expands in volume, becomes less dense, and accumulates on the surface. Therefore, the water freezes first on the surface, followed by towards the bottom and
Extending around, a sealed "ice shell" is formed. At this time, the inner water is isolated from the outside air and can only rely on conduction and radiation to dissipate heat. Therefore, the cooling rate is very small, preventing or delaying the temperature of the inner water.
It continues to descend normally. In addition, because the volume of water expands when it freezes, the "ice shell" that has been formed also plays a certain role in constraining or inhibiting further freezing. A cup containing hot water with an initial temperature of 100℃, frozen
Relatively speaking, the time is much less. What we can see is that the ice layer on the surface can never be connected to form an ice cap. We cannot see the formation of "ice shell". We can only see the needle-like growth along the interface of ice and water into the liquid.
Ice crystals (this phenomenon cannot be seen when the initial temperature is lower than 12°C). As time goes by, the ice crystals change from fine to thick. This is because the hot water with high initial temperature becomes denser after the upper water cools down.
The flow forms convection inside the liquid, causing water molecules to form ice around their respective "crystallization centers". The higher the initial temperature, the more intense the convection and the greater the energy loss. It is this convection that causes the upper layer to form ice.
The water is not easy to form ice sheets. Due to heat transfer and phase change latent heat, the internal energy loss per unit time is large and the cooling rate is large. When the water surface temperature drops below 0℃ and there is sufficient low temperature, the water surface begins to
Ice crystals appear. Water with a higher initial temperature grows ice crystals at a faster rate. This is due to the fact that the ice cap has not formed and the convection is intense. In the end, it can be observed that the ice cap is still formed, and the cooling rate becomes smaller, but because the water
The internal ice crystals have grown and are thick, and have a large surface energy. The growth rate of the ice crystals is proportional to the unit surface energy, so the growth rate is still much faster than that of water with a low initial temperature."
"Stop, stop, stop!!!" Wang Kai was confused by Li Mulin's long speech. He had no idea about the refrigeration mechanism or the cooling rate, so he interrupted Li Mulin's answer without politeness.
"You should give a simple answer." Wang Kai wiped the sweat from his forehead and asked Li Mulin to continue talking. He would probably go crazy.
Li Mulin took out his hand from his trouser pocket, spread it and said, "I've finished speaking."
In his trouser pocket, an extremely small voice said: "The cost of breaking into the Physics Data Center of the Chinese Academy of Sciences is eighteen thousand eight hundred and eighty-eight. Counting your friendship price, it is twenty thousand. Remember to pay it to my card."
Li Mulin pursed his lips without any trace. The original price was 18,880, and he was charged 20,000. This was also called a friendship price, but he had no chance to refute at this time. Although he felt a bit cheated,
Li Mulin still admires Heisi very much. He is even more powerful than Nobita's Doraemon. He is basically omnipotent. He originally had the mentality of giving it a try, but he didn't expect that Heisi would solve it for him, but at the cost
Yes, Li Mulin had to borrow some money from a buddy again.
At this time, there was silence all around, and everyone was shocked by Li Mulin's wonderful answer. Although Wang Kai, the second generation ancestor, did not understand, there were still some good students who could understand Li Mulin's explanation. Even the person who asked the question
The professor of the Department of Physics was sweating profusely at this time. In fact, even he didn't know the answer to this question, so he concluded that Li Mulin couldn't answer it. But now Li Mulin not only answered it, but also it was almost watertight.
From a certain perspective, Li Mulin's answer is perfect. Of course, this is only one aspect of the results explored by scientists. The real reason has yet to be explored, but despite this, Li Mulin's answer is definitely not
The calculation is wrong because it is recognized by many scientists.
"What do you call answering questions? I think you are talking nonsense!" Since there was no answer, Wang Kai didn't know whether Li Mulin answered correctly. He thought that Li Mulin didn't know how to answer and was just talking nonsense, so he filmed
shouted at the table.
Li Mulin just glanced at Wang Kai with disdain. For such a guy who was full of sperm but had no money in his stomach, Li Mulin didn't bother to explain to him and asked him to answer this question by himself. He really couldn't answer it.
But he was able to tell the difference, and even if his answer was incorrect, it could never be wrong.
"Professor Liu Yichang, tell him that his answer is complete nonsense!" Wang Kai was eager to expel Li Mulin from D University, and he was a little excited. His words sounded a bit commanding.
The displeasure on Liu Yichang's face flashed away, and he said expressionlessly: "Instructor Li Mu's answer is completely correct, I will give you ten points." After saying that, he picked up the scoring board in his hand and wrote a big ten points.
Liu Yichang's move undoubtedly slapped Wang Kai hard. There are many people in University D who dare not offend Wang Kai, but it is a pity that Liu Yichang is not in this group. He has been a leader since the founding of the school until now.
He is an old professor and has great prestige in the college. Even Wang Bifu is polite to him, so he is not afraid of offending Wang Kai at all.
"You!" Wang Kai wanted to say something else, but Wang Bifu glared at him fiercely. Wang Kai sat back on the stool angrily, with a sullen face and said nothing.
"Young man, good job." As if he didn't think it was enough to attack Wang Kai, Liu Yichang also gave Li Mulin a thumbs up.
Li Mulin nodded without humility, with a proud smile on his face, as if he had solved the problem himself.
"There are still five tests. I don't believe I can't kill you!" Wang Kai's hands clenched tightly into fists.