Chapter 59 Want a Fake Article? I Test You Twice
In the three days of the Mathematical Modeling Contest, two big things classes will be washed away.
Although it was an order to ask for leave, considering that it is not good to ask for leave in the first class, Lu Zhou decided to send the leave slip in person, so that he would not bother the monitor to do it for him.
Looking at the timetable information given by the Academic Affairs Office, Mr. Dawu's name is Li Rongen, 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 went over with the fake note.
After knocking on the door, Lu Zhou walked in and put the slip on the desk, explaining his purpose.
"Ask for leave?" Looking at the slip, Professor Li took off his reading glasses, raised his head and smiled, "Your name is Lu Zhou, right?"
"Yes." Lu Zhou nodded.
Professor Li smiled and said, "Well, I will test you two questions. If you solve one, I will approve your fake test."
And this kind of operation? !
Lu Zhou was dumbfounded.
"What? Scared?" Li Rongen asked with a smile.
"No," Lu Zhou calmed down, shook his head and said, "Teacher, please answer the question."
"The first question, take it." Throwing a piece of A4 paper into Lu Zhou's hand, Li Rongen looked at Lu Zhou with a smile, and the old god said in the ground, "How much can be written, I will see the process."
Are you ready for the topic? !
Lu Zhou always felt that this guy was premeditated, otherwise how should he explain why this question has been printed on A4 paper?
However, even if he guessed a little, Lu Zhou didn't say anything, picked up the A4 paper and began to read the question.
[The half-life of the U238 nucleus in the nuclear submarine is 4.5×10^9 years, and there is a 0.7% probability of decay to become the U234 nucleus, and at the same time, a high-energy photon is released, and 93% of these photons are absorbed by the submarine steel plate. In 1981, the high-energy photons transmitted to the outside of the nuclear submarine of the former Soviet Union numbered U137 were measured by a detector at a distance of 1.5m from the nuclear source (processed as a point). The normal incidence area of the instrument is 22cm^2, the efficiency is 0.25% (every 400 incident photons can generate a pulse signal), and 125 signals are measured per hour.
① Find the average lifetime 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 title, Lu Zhou sighed softly in his heart.
As expected of Professor Li, who was dubbed the "Four Demons of the Courtyard" by previous seniors, is this the kind of problem when he shoots?
In other words, the first big thing class will only be held next Monday, and I will directly test myself with this kind of nuclear physics knowledge that is beyond the outline. Is it really okay?
"Do you want to find a place to sit?"
"No need, just here."
After taking the pen and scratch paper that Professor Li handed over, Lu Zhou stood beside the desk, frowned, and thought for a moment.
Physics is really not his area of expertise.
However, after a summer vacation, he was impeccable!
About five minutes later, Lu Zhou's brows loosened, and the tip of the pen 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 T1/2=ln2/λ can be obtained
】
After writing these two lines of calculations, Lu Zhou's eyes flickered slightly.
He has succeeded in turning physics problems into high-number problems.
The next step is to break them one by one!
First ask first!
The nib swam quickly across the A4 paper.
[(1) The average lifetime of radionuclides t=∫λNtdt/N0=…=1.1443T1/2
Substitute into the data, t=6.49*10^9 years.
】
Glancing at the A4 piece of paper, Professor Li Rongen raised his eyebrows, and an interesting look appeared in his eyes.
Not noticing the change in Professor Li's expression, Lu Zhou, who was highly focused on the paper, began to answer the next question.
[From the information of the question, it can be obtained that the number of high-energy photons generated by decaying into U234 at dt time is -dN·n0=n0λNdt
Then 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
The number of photons entering the detector...
The number of signals generated in the detector...
Calculate the number of U238 in the submarine, and thus calculate the number of U238 cores.
】
Lu Zhou substituted all the data and calculated the number of U238 cores in the submarine N=7.456*10^25.
However, just when he was about to bring N into M=N*238u and finish the final blow to the enemy's spring, Professor Li Rongen suddenly spoke up.
"Okay, forget about you."
Lu Zhou: ? ? ?
He was immediately unhappy.
What do you mean I have passed?
I'm all here, can't you wait for me to finish talking!
"Professor, I'm not finished yet..."
"It's all calculated by you, even if you find a junior high school student, you can figure it out," Li Rongen said with a smile, "You can finish the calculation if you want.
The atmosphere of doing the question was completely destroyed, and Lu Zhou was speechless for a while.
Unable to bear the entanglement of obsessive-compulsive disorder, he still wrote the result at the end.
The answer M=29.634kg, taking two digits is about 30kg
The steps are correct, and the results are correct without any suspense.
Lu Zhou drew a successful conclusion to this question.
"Would you like to hear the second question?" Li Rongen said with a smile.
Although Lu Zhou wanted to say "I don't want to", but thinking that the professor has not approved his fake note, he couldn't help but say: "Go ahead."
Li Rongen smiled and continued: "Don't be nervous, the second question is very simple, just tell me, this is Kennan's expression of the second law of thermodynamics."
Hearing this question, Lu Zhou breathed a sigh of relief.
Originally, he thought that the second question of this professor would be a difficult problem that he could not write at all, and he was told not to be complacent or anything, but he didn't expect that Professor Li didn't play cards according to the routine, so he simply let it go. he is.
Generally speaking, there are two main formulations of the second law of thermodynamics, one is the famous Kelvin formulation, and the other is the formulation mentioned by Clausius in his 1850 paper.
As for Kennan's formulation, it is a relatively new formulation that has recently emerged.
Be careful when you read the textbook, you won't miss it.
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 reached through a reversible process." Lu Zhou repeated this statement as if he was reciting the text.
"Not bad." Li Rongen nodded approvingly.
In the textbooks used by non-physics majors, this more cutting-edge expression will not be mentioned in the main text, but it will still be mentioned in the appendix. Generally, students who have no interest in physics will not go there after graduation.
If Lu Zhou has grasped this obscure knowledge point so clearly, it is enough to prove that he has thoroughly read the entire textbook of "University Physics".
After this shallow and in-depth investigation, Li Rongen can now confirm that his course for undergraduate non-physics students really has nothing to teach him.
It seems that Lao Tang really did not brag, this kid is a talent!
In fact, if you answer the question correctly, you will only be granted leave. That is all a joke with young people.
Since yesterday, he has approved dozens of fake slips for the Mathematical Modeling Contest, how could there be such a slip?
Even if Lu Zhou couldn't answer, he would only make a few jokes at most, and he would finally approve.
After signing the slip, Li Rongen took out the roll call book in the drawer, drew two ticks on it, and said in the tone of an elder.
"Lu Zhou."
"What's wrong?"
"Any plans to go to graduate school?"
Lu Zhou thought about it, and said in an uncertain tone, "Yes."
Who's to say the future?
However, Professor Li's intuition was obviously not as sharp as Old Tang's. He didn't hear the uncertainty in Lu Zhou's tone at all. Instead, he nodded in approval and continued.
"Our Department of Physics at King's University is considered to be at the top level among colleges and universities in the country. To be modest, even if Peking University and us are tied for the first place. However, if it is specific to the research direction, superconducting physics and strongly correlated electronic systems, and In the fields of condensed matter physics and material design, they are not as good as us. If you are interested in physics, you can come to me during the postgraduate entrance examination. Our carbon nanotube laboratory needs top talents in the field of mathematics.”
This is……
Are you implying me to apply for his graduate school in the future?
Lu Zhou couldn't help laughing and laughing in his heart. He is just a sophomore and is still far from the postgraduate entrance examination.
But in any case, this is the teacher's kindness.
Lu Zhou said sincerely: "Thank you, teacher."
Li Rongen smiled and nodded: "Okay, take the fake note. You have the opportunity to participate in this kind of competition. If you are not good at politics, you can pay attention to the opportunity of Baoyan. Or when you are in your junior year next year, come here. Ask me, ask you Teacher Tang, you can."
Lu Zhou thanked him with a smile. He didn't say more, and took this hard-won note to leave quickly.
Continue to put bowls for recommendation tickets~~~~