The three days of the mathematical modeling competition was enough to cancel two physics classes.
Although Lu Zhou was taking a leave of absence, he considered that it would not be good to take a leave of absence in the first class. Therefore, he decided to personally send the leave slip so that the class leader would not have to do it for him.
Looking at the timetable given by the Academic Affairs Office, the physics teacher's name was Li Rongen. He was an old professor with high qualifications. After Lu Zhou asked for the teacher's phone number in the school chat group, he made a call and confirmed that the teacher was in the office. He then took the leave of absence to the teacher.
Lu Zhou knocked on the door and walked in. He placed the leave of absence on the desk and explained his intentions.
"Leave of absence?" Professor Lee looked at the leave of absence and took off his glasses. He looked up and said, "Your name is Lu Zhou, right?"
"Yes," said Lu Zhou as he nodded.
Professor Lee smiled and said, "Okay then, I'll test you with two questions. If you can solve one, I'll approve your leave."
There's such a thing?!
Lu Zhou was dumbfounded.
"What? Scared? "asked Lee Yong-eun with a smile.
"No," said Lu Zhou as he shook his head. He then said, "Teacher, you can choose the question."
"First question, take it," said Lee Yong-eun as he threw a piece of A4 paper into Lu Zhou's hand. He smiled at Lu Zhou and said, "Write as much as you can, I want to see the process."
He even prepared the question?!
Lu Zhou felt like this guy was premeditated. Otherwise, why would he print the question on an A4 paper?
However, even though Lu Zhou guessed this, he did not say anything. He picked up the A4 paper and began to read the question.
[The half-life of the U238 nucleus in a nuclear submarine is 4.5 × 10 ^ 9 years. There is a 0.7% probability of becoming a U234 nucleus during decay. At the same time, it emits a high-energy photon. 93% of these photons are absorbed by the submarine's steel plate. In 1981, the high-energy photons transmitted out of the former Soviet Union nuclear submarine U137 were detected by a detector 1.5m away from the nuclear source (processed as a dot). The forward incident area of the instrument was 22cm ^ 2, and the efficiency was 0.25% (every 400 incident photons could produce a pulse signal). It could measure 125 signals per hour.
① Find the average life of the U238 nucleus and find the mass of the U238 in the nuclear submarine (the unit is kg, take 2 digits).
】
After reading the question, Lu Zhou sighed in his heart.
As expected of Professor Lee, who was named as one of the "Four Devils of the Academy of Physics" by the seniors of the previous years. Did he come up with such a question as soon as he started?
Speaking of which, the first physics class would start next Monday. Was it really okay to test him on nuclear physics, which was beyond the scope of the syllabus?
"Should we find a place to sit down?"
"No need, let's do it here."
Lu Zhou took the pen and draft paper from Professor Lee and stood next to his desk. He frowned and thought for a moment.
Physics was indeed not his area of expertise.
However, after a summer's worth of intensive study, he was invulnerable as he stood here!
Around five minutes later, Lu Zhou's eyebrows relaxed and the pen began to move.
[Law of decay of radionuclides: N = N0e ^ (-λt)]
The relationship between the decay constant and half-life is: N0/2 = N0e ^ (-λT 1/2), from which T1/2 = LN2/λ]
】
After writing down these two lines of calculations, Lu Zhou's eyes lit up.
He had successfully turned a physics problem into an advanced mathematics problem.
Next, he had to solve them one by one!
First question!
The pen quickly moved on the A4 paper.
[(1) The average life of radionuclides t = the years available for substitution.
】
Professor Lee Yong-eun looked at the A4 paper and raised his eyebrows. He had a look of interest in his eyes.
Lu Zhou did not notice the change in Professor Lee's expression. He was highly focused on the paper and began to answer the next question.
[From the information in the question, the number of high-energy photons produced by decay into U234 in dt time is -dN · n0 = n0λ Ndt.
Then let the efficiency of photons passing through the steel plate be n1. The number of photons passing through the steel plate in dt time is calculated to be dN1 = n0λ Ndt · n1.
The number of photons entering the detector …
The number of signals generated in the detector …
Calculate the number of U238 in the submarine, and then calculate the number of U238 cores.
】
Lu Zhou substituted all the data and calculated the number of U238 cores in the submarine, N. However, he was about to bring N into M = N * 238u and complete the final blow to the enemy's spring water when Professor Lee Yong-eun suddenly spoke.
"Alright, you've passed."
Lu Zhou:???
He was suddenly unhappy.
What do you mean I passed?
I've already calculated this far, can't you wait for me to finish!
"Professor, I haven't finished yet …"
"You've already calculated this far, even a middle school student can do it." Lee Yong-eun said with a smile, "You can do it if you want."
The atmosphere was ruined, and Lu Zhou was speechless.
He couldn't resist his obsessive-compulsive disorder, so he still wrote down the result at the end.
The answer M was about 30kg.
The steps were correct, and the result was correct.
Lu Zhou drew a perfect full stop for this question.
"Do you want to hear the second question?" asked Lee Yong-eun with a smile.
Although Lu Zhou wanted to say "no", he remembered that the professor had not approved his leave yet, so he said, "Go ahead."
Lee Yong-eun smiled and said, "Don't be nervous, the second question is very simple. Tell me about the Kennan expression of the second law of thermodynamics."
When Lu Zhou heard this question, he sighed in relief.
Initially, he thought that Professor Li's second question would be a difficult question that he couldn't answer at all. Professor Li would warn him not to be arrogant or complacent. However, he didn't expect that Professor Li wouldn't play by the rules and would let him off so easily.
Generally speaking, there were two main expressions of the second law of thermodynamics. One was the famous Kelvin expression, and the other was the expression mentioned in Clausius' 1850 paper.
As for Kennan's expression, it was a relatively new expression that had recently been developed.
If one was careful when reading the textbook, they wouldn't miss it.
Which was —
"For a system with a given energy, material composition, and parameters, there is such a stable equilibrium state. The other states can always be achieved through a reversible process," said Lu Zhou as he recited the statement.
"Not bad," said Lee Yong-eun as he nodded with approval.
Textbooks for non-physics majors wouldn't mention this kind of cutting-edge expression in the main text, but it would still be mentioned in the appendix. Generally speaking, students who were not interested in physics would not read it after they graduated.
If Lu Zhou could grasp this obscure knowledge so clearly, it was enough to prove that he had thoroughly understood the entire "University Physics" textbook.
After this in-depth investigation, Lee Yong-eun could now confirm that there was nothing for him to teach non-physics undergraduate students.
It seemed that Professor Tang was not bragging. This kid was a genius!
In fact, saying that he would only approve leave if he answered correctly was a joke.
Since yesterday, he had approved dozens of leave slips for the mathematical modeling competition. How could he miss this one?
Even if Lu Zhou couldn't answer, he would at most tease him a little and would approve it in the end.
After signing the leave slip, Lee Yong-eun took out the name list from his drawer. He drew two ticks on it and spoke in a senior tone.
"Lu Zhou."
"What?"
"Do you have any plans to go to graduate school?"
Lu Zhou thought for a bit and said in an uncertain tone, "Probably."
Who knows what the future holds?
However, Professor Lee's intuition was obviously not as sharp as Professor Tang's. He did not hear the uncertainty in Lu Zhou's tone. Instead, he nodded and continued to speak.
"Our Nanjing University's physics department is considered one of the top universities in the country. Humbly speaking, Peking University is tied with us. However, in terms of specific research areas, such as superconducting physics and strongly correlated electronic systems, condensed matter physics, and material design, they are not as good as us. If you're interested in physics, you can come find me when you're taking the postgraduate exams. Our carbon nanotube laboratory needs top talents in the field of mathematics. "
This is …
Is he hinting at me to become his postgraduate student?
Lu Zhou did not know whether to laugh or cry. He was only in his second year and was still far from his postgraduate exams.
Regardless, this was his teacher's good intentions.
Lu Zhou said sincerely, "Thank you, teacher."
Lee Yong-eun smiled and nodded, "Okay, take your leave slip. If you have the chance to participate in this kind of competition, if you can't do politics, you can look for a postgraduate recommendation. Or when you're in your third year next year, you can ask me or Professor Tang. "
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