Chapter 59: Want a fake note? I test you 2

In the three days of the Mathematical Modeling Contest, two big class lessons will happen.
Although he asked for leave on purpose, considering that the first lesson was not good, Lu Zhou decided to send the leave in person, so he wouldn't bother the squad leader to do it for him.
Looking at the schedule information given by the Academic Affairs Office, the teacher named Li Rongen is an old professor with high qualifications. After asking for the phone number in the school group, Lu Zhou made a phone call to confirm that the teacher was in the office, and then passed over with a fake note.
After I knocked on the door, Lu Zhou went in and put the dummy on the desk, explaining his intention.
"Ask for leave?" Looking at the leave strip, Professor Li took off the reading glasses, raised his head and smiled, "Your name, Lu Zhou, right?"
"Yes." Lu Zhou nodded.
教授 Professor Li smiled and said, "In that line, I will take two questions from you. If you solve them one by one, I will approve your false note."
Still this kind of operation? !!
Lu Lu was dumbfounded.
怎么 "What? Scared?" Li Rongen asked with a smile.
"No," Lu Zhou calmed down and shook his head. "Teacher, let me ask you a question."
"The first question, take it," he threw an A4 piece of paper into Lu Zhou's hands, Li Rongen looked at Lu Zhou with a smile, and the old said on the ground, "I can write as much as I want, I want to see the process."
Are you ready for the question? !!
Lu Zhou always feels that this guy has a premeditated plan, otherwise how can I explain it, why is this question printed on A4 paper?
However, even if he guessed a little, Lu Zhou said nothing, picked up A4 paper and started reading 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 that the U234 nucleus will become a U234 nucleus while emitting a high-energy photon. 93% of these photons are absorbed by the submarine steel plate. In 1981, the high-energy photons transmitted by the nuclear submarine U137 of the former Soviet Union out of the boat were measured by a detector 1.5m away from the nuclear source (processed as a point). The instrument's normal incidence area is 22 cm ^ 2, the efficiency is 0.25% (a pulse signal can be generated for every 400 incident photons), and 125 signals are measured per hour.
① Find the average life of the U238 core (ln2 = 0.693).
② Find the mass of U238 in the nuclear submarine (unit: kg, take 2 digits)
]
After reading the topic, Lu Zhou sighed softly.
He is indeed Professor Li, who was named "Four Devil of the Museum" by his predecessors. Is this the first shot?
Speaking of which, the first big class lesson will be held next Monday, and you can test yourself with this kind of nuclear physics knowledge. Is it really okay?
"Somewhere to sit and count?"
"No, just here."
He took the pen and draft paper handed over by Professor Li, and Lu Zhou stood by his desk, frowning, and pondered for a moment.
Physics is really not his area of ​​expertise.
However, after a blast of learning during the summer vacation, he is invincible!
About five minutes later, Lu Zhou's brows fell loose and his pen tip moved.
【The decay law of radionuclides: N = N0e ^ (-λt)
The relationship between the decay constant and the half-life is: N0 / 2 = N0e ^ (-λT1 / 2), from which we can obtain T1 / 2 = ln2 / λ
]
I wrote these two lines of calculations, and Lu Zhou's eyes flickered slightly.
He has successfully turned the physics problem into a high number problem.
Next, they are broken one by one!
Ask first!
The nib swam quickly on A4 paper.
[(1) Average life of radionuclide t = ∫λNtdt / N0 = …… = 1.1443T1 / 2
Substituting data can be obtained, t = 6.49 10 ^ 9 years.
]
Glancing at the A4 paper, Professor Li Rongen raised his eyebrows, and a funny look appeared in his eyes.
He didn't notice the change in Professor Li's expression. He focused on Lu Zhou on the paper and began to answer the next question.
[It can be solved from the stem information that the number of high-energy photons that decay into U234 at dt time is -dN · n0 = n0λNdt
Set the efficiency of photons passing through the steel plate as n1, and calculate the number of photons passing through the steel plate in dt time as dN1 = n0λNdt · n1
数 Number of photons entering the detector ...
The number of signals generated by the radon detector ...
Calculate the number of U238 in the submarine, and calculate the number of U238 cores from it.
]
Lu Zhou substituted all the data to calculate the number of U238 cores in the submarine N = 7.456 10 ^ 25.
However, just as he was about to bring N into M = N 238u, and completed the final blow to the enemy's spring, Professor Li Rongen suddenly spoke.
"Well, you're over."
Lu Zhou :? ? ?
Suddenly he was unhappy.
What do you mean I passed?
I've counted here, can't you wait for me to finish talking?
"Professor, I haven't finished counting ..."
"It's all up to you, you can figure it out for a junior high school student," Li Rongen said with a smile, "you can count it as you wish, whatever you want."
的 The atmosphere of the question was destroyed, and Lu Zhou was speechless for a while.
He couldn't resist the entanglement of obsessive-compulsive disorder, and he wrote the result at the end.
Answer M = 29.634kg, which is about 30kg with two digits
The steps are correct, and the results are correct.
Lu Zhou put a complete end to this question.
"Do you want to hear the second question?" Li Rongen said with a smile.
Although Lu Zhou wanted to say "don't want to", but thought that the professor had not approved his own fake note, he could not help but said, "You say it."
Li Rongen smiled and continued, "Don't be nervous, the second question is very simple, just tell me about Kennan's expression of the second law of thermodynamics."
Hearing this, Lu Zhou was relieved.
Originally, he thought that the second question of this professor would debut a problem he couldn't write and beat him, telling him not to be proud and complacent, but he did not expect that Professor Li did not follow the routine at all. He's gone.
Generally speaking, there are two main expressions of the second law of thermodynamics, one is the famous Kelvin expression, and the other is the expression mentioned by Clausius in his 1850 paper.
As for Kennan's expression, it is a relatively new expression method recently produced.
认真 Be careful when watching the textbooks, so you won't miss them.
which is--
"For a system with a given energy, material composition, and parameters, there is such a stable equilibrium state: other states can always be achieved through reversible processes." Like a lesson, Lu Zhou repeated this expression.
"Yes." Li Rongen nodded approvingly.
较为 In the textbooks used by non-physics majors, this more advanced statement is not mentioned in the text, but it will still be mentioned in the appendix. Students who are generally not interested in physics will not turn there after graduation.
If Lu Zhou has mastered this indistinct knowledge point so clearly, it is enough to prove that he has eaten the entire textbook of College Physics.
After this shallow and in-depth inspection, Li Rongen can now confirm that there is really nothing to teach him in this course for undergraduate non-physics majors.
It seems that Tang did not brag, this kid is a personal talent!
In fact, what is said to answer the question correctly before approving leave, that is all a joke with young people.
Since yesterday, he has approved dozens of fake bars in the mathematical modeling contest ~ EbookFREE.me ~ Why a fake bar?
Even if Lu Zhou couldn't answer, he would tease a few words at most, and he would still approve in the end.
Signed the fake note, Li Rongen turned out the roll book in the drawer, and while drawing two ticks on it, said in an elder tone.
"Lu Zhou."
"what happened?"
"Are there any plans to study?"
Lu Zhou thought for a while and said in an uncertain tone, "Yes."
谁 Who told the future?
However, Professor Li's intuition was obviously not as keen as Lao Tang, and he could not hear the uncertainty in Lu Zhou's tone at all. Instead, he nodded in approval and continued.
"Our Department of Physics at NTU is regarded as the top level among universities in the country. In terms of modesty, even if Peking University is tied with us first. But if it is specific to the research direction, superconducting physics and strongly related electronic systems, and cohesion They are not as good as us in the fields of dynamic physics and material design. If you are interested in physics, you can come to me when you are studying for admission. Our carbon nanotube laboratory needs top talent in the field of mathematics. "
this is……
Was he hinting at me and reporting to his graduate student later?
舟 Lu Zhou couldn't help crying and laughing. He was just a sophomore now, and he was still far from the postgraduate entrance examination.
But anyway, this is the kindness of the teacher.
Lu Zhou sincerely said, "Thank you."
Li Rongen smiled and nodded: "Okay, go ahead and take a fake note. This kind of competition has the opportunity to participate in more, if your politics. Governance does not work, you can pay attention to the opportunity of insurance research. Or wait until next year when you arrive in junior year, come Ask me, ask you Mr. Tang. "
Lu Zhou smiled and expressed his thanks, didn't talk much anymore, and quickly left with this hard-won fake note.