Chapter 12 Do the questions after entering the door
"Brother Chuan is here."
"Brother Chuan, I heard that you went to the math competition this year. How was it there? Was it fun?"
"I heard that this year's number competition is difficult. There are only twelve people who got full marks in the provincial competition, and Brother Chuan is one of them!"
"Not only that, don't forget that Brother Chuan also scored perfect marks in the provincial competition of our sports competition."
"Awesome! As expected of Brother Chuan. This is the last time. Brother Chuan definitely wants to win a double gold medal."
At Yali Middle School, with the arrival of Xu Chuan, the provincial training team quickly became lively, and all the students in the classroom joined in.
As someone who has made it to the provincial team for three consecutive years, most of the students in front of him know Xu Chuan.
After all, those who can enter the provincial team are basically students in their second and third years of high school. Students who came to experience the competition in their first year of high school also got to know this great figure through the introduction of old students.
A player who can win a silver medal in a world-class competition in his sophomore year of high school is regarded as an incredibly powerful player in the eyes of all students participating in the competition.
After all, the gap between digital competition and physical competition is still quite large. It is too difficult to reach the top in both aspects.
Xu Cheng threw the chalk tip in his hand towards the podium, stared at Xu Chuan and said.
So he planned to use the questions to test it. If there was no progress, don't blame him for the next month when his subordinates practiced ruthlessly to death.
After all, human energy is limited. If you engage in mathematics, you will have less energy to focus on physics.
However, expectations were expectations, and Xu Chuan was still a little dissatisfied when he went to engage in a number competition.
The difficulty level is almost the same as that of IPHO. Putting it on IPHO, it is almost the penultimate question type.
Outside the noisy classroom, an unexpected sound came.
If the first question is 1+2=3, then the difficulty of the second and third questions increases to the point of proving 1+2=3.
"Hey, Xu Chuan is here."
And I heard from the old guy at the math competition that his math ability is stronger than his physics ability.
Moreover, he is obviously a genius discovered in physics, so what does it mean to snatch someone away from him in the middle of mathematics?
If you don't just want to rob people, why do you want so much money?
It’s not that there are no people who participate in math competitions and physical competitions at the same time, but in recent years, there are no people in southern Hunan who can enter the provincial team and enter the golden autumn camp and winter camp at the same time. There are a few in Mingyue City and Zhongcheng.
Xu Cheng scoffed at this statement.
But the difficulty of the second and third parts skyrocketed, and it was like riding a rocket. Whether it was to find the root-mean-square velocity based on the average kinetic energy of the atom, or to find the de Broglie wavelength after finding the momentum, the difficulty was not ordinary.
High school students can handle it.
The difficulty of finding the distance between particles in the third step is even higher.
Xu Cheng is still looking forward to Xu Chuan.
This question is about Bose-Einstein condensates. The whole question has three parts. The first part is not very difficult and can be solved if you have a certain foundation in physics.
He is very clear about this student's physics ability and learning ability. He can get a silver medal in IPHO after one and a half years of study, and there is a high probability that he will win a gold medal this year.
"This question is relatively difficult. It applies some mathematical knowledge. You can use it as an extracurricular test. If you are interested, you can try to solve it. Except for Xu Chuan, please give me the answer tomorrow morning. I heard that you are taking the provincial math competition test.
If you get full marks, it shouldn’t be difficult for you.”
After saying hello, Xu Cheng picked up the chalk on the podium, stood in front of the blackboard and thought for half a minute, and then started to write.
There are only two or three people who can be selected into the national training teams for mathematics and physics in the same year. From the time when domestic teams were formed to participate in international competitions in the 1990s to now, more than 30 years ago.
Second, calculate the functional relationship between the typical distance l between particles in the gas and the particle number density n. Then derive the expression of critical temperature Tc, expressed in terms of atomic mass, density and physical constants.
Xu Cheng looked at the student in front of him with a smile and nodded, as a greeting.
The corner of Xu Chuan's mouth twitched, and he probably understood that this was Xu Cheng's dissatisfaction, dissatisfaction with him running away to participate in the math competition.
1. For non-interacting 87Rb gas atoms in thermal equilibrium, write down the expressions of their typical momentum p and de Broglie wavelength λdB, expressed in terms of atomic mass m, temperature T and physical constants.
"This is an interesting quantum collective state achieved through phase transition."
Under the podium, all the students looked confused and wondered whether they had traveled through time on the first day of training.
Don’t even think about it!
The student in front of me was taught by him last year, but I heard that he participated in the math competition this year and got full marks to enter the provincial team.
Third, in order to achieve BEC in the laboratory, experimenters need to lower the temperature of the gas to Tc=100nK.
"Teacher Xu."
There is no one in China who can win gold medals at both IMO and IPHO in the same year.
"Bosons do not obey the Pauli exclusion principle and experience dramatic Bose-Einstein condensation (BEC) phenomena at low temperatures or high densities."
What is written here? I can’t understand it no matter how I read it?
Only a few students frowned and stared at the question on the blackboard that almost occupied the entire blackboard.
Such a talented person doesn't come to study physics, but to learn mathematics from a model worker?
Xu Chuan turned around and greeted the visitor respectfully.
But seriously, ordinary high school students may not be able to solve this problem, even if they have the ability to join the national training team.
".BEC occurs when the de Broglie wavelength corresponding to the root mean square velocity of atoms is approximately equivalent to the characteristic distance between particles in the gas.
"Come on, let's do some questions first and let me see your learning results in the past year."
If BEC occurs at this temperature, what is the number density nc of 87Rb gas? For the convenience of comparison, the number density n0 of ordinary ideal gas at standard temperature and pressure is also calculated, that is, T0=300K, p0=105Pa, and the mass of the atom can be assumed
It is equal to 87 atomic mass units (mamu). How many times is the density n0 of ordinary gas nc?
Compared with the math competition questions, the calculation amount of this question is actually not large, but it requires the solver's logical ability and application ability to be very high.
But this is the ability required to study physics.
After all, the difference between physics and mathematics is quite big.
In the process of systematic learning, the difficulty of mathematics lies in the cultivation of thinking, while the difficulty of physics lies in the application of knowledge and methods.
