"Brother Chuan is here."

"Brother Chuan, I heard that you went to the math competition this year, how is it over there, is it fun?"

"I heard that this year's number of competitions is difficult, and there are only twelve people who have scored full points in the provincial competition, and Brother Chuan is one of them!"

"Not only that, don't forget the provincial competition of our physical competition, Brother Chuan is also a full score."

"Awesome! is worthy of Brother Chuan, the last one, Brother Chuan definitely wants to win a double gold medal. ”

Yali Middle School, with the arrival of Xu Chuan, the provincial training team quickly became lively, and all the students in the classroom came over one after another.

As a person who has been in 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 the second and third years of high school, and the students who came to experience the competition in the first year of high school also got to know this god-level figure under the introduction of the old students.

The player who can win the silver medal in the world-class competition in the second year of high school, in the eyes of all the students who participate in the competition, the cliff is too strong to be a god.

.......

"Yo, Xu Chuan is here."

Outside the noisy classroom, an unexpected voice came.

Xu Chuan turned his head to look at it, and said hello respectfully when he saw someone coming.

"Teacher Xu."

Xu Cheng looked at the student in front of him with a smile and nodded, which was regarded as a greeting.

The student in front of him was brought by him last year, but I heard that he participated in the mathematics competition this year and got a full score to enter the provincial team.

And I heard the old guy over there say that his mathematical ability is stronger than his physical ability.

Xu Cheng scoffed at this statement.

Don't you just want to rob people, why are you doing so many flowers?

It is not impossible to participate in the number competition and the physical competition at the same time, but those who can enter the provincial team and enter the golden autumn camp and winter camp at the same time have not been in Xiangnan in recent years, but there are a few in Mingyue City and Zhongcheng.

In the same year, there is no gold medal in IMO and IPHO at the same time.

Those who can be selected for the national training team of digital competition and physical competition at the same time in the same year have only been two or three people for more than 30 years, from the beginning of the formation of domestic teams to participate in international competitions in the 90s.

After all, the gap between digital competition and physical competition is still quite large, and it is too difficult to stand at the top in both aspects.

For Xu Chuan, Xu Cheng is still looking forward to it.

He knows very well that this student's physical ability and learning ability can win a silver medal in the IPHO after a year and a half of study, and there is a high probability that he will win a gold medal this year.

However, looking forward to it, Xu Chuan ran to engage in a number competition, and he was still a little dissatisfied.

After all, human energy is limited, and if you go to mathematics, then you will have less energy to focus on physics.

So he plans to use the question to test it, and if there is no progress, don't blame his subordinates for ruthlessly practicing to the death in the next month.

Such a good genius, don't come to learn physics, to learn labor model mathematics?

And it's obviously a genius discovered by physics, what's the matter of robbing people in the middle of mathematics?

Don't even think about it!

.......

"Come on, come on, do the questions first, and let me see your learning results in the past year."

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 began to write.

"Bosons do not follow Pauli's principle of incompatibility and, at low temperatures or high densities, experience dramatic Bose-Einstein condensation (BEC)."

"It's a ...... that achieves an interesting quantum collective state through a phase transition"

“...... BEC occurs when the de Broglie wavelength, which corresponds to the rms rate of an atom, is approximately equivalent to the characteristic distance between the particles in the gas.

1. For the non-interacting 87Rb gas atoms in thermal equilibrium, write the expressions of their typical momentum p and de Broglie wavelength λdB, expressed by atomic mass m, temperature T and physical constant.

2. Calculate the relationship between the typical distance l between particles in a gas and the particle number density n. The critical temperature Tc expression is then derived, which is expressed by atomic mass, density and physical constant.

3. In order to achieve BEC in the laboratory, the experimenters need to reduce the temperature of the gas to Tc=100nK.

If BEC occurs at this temperature, what is the number density nc of 87Rb gas? For the sake of comparison, the number density n0 of the ordinary ideal gas at standard temperature and air pressure is also calculated, that is, T0 = 300 K, p0 = 105Pa, and the mass of the atom can be assumed to be equal to 87 atomic mass units (mamu), how many times is the density of the ordinary gas n0 compared to nc?

Under the podium, all the students were confused, wondering if they had crossed the first day of training.

What is this written about? Can't understand how to look at it?

Only a few students frowned, staring at the blackboard that occupied almost an entire blackboard.

"The difficulty of this question is relatively large, some mathematical knowledge is applied, you can use it as an extracurricular test question, you can try to solve it if you are interested, except for Xu Chuan, you give me the answer tomorrow morning, I heard that you have a full score in the provincial competition, it should not be difficult for you."

Xu Cheng threw the chalk head in his hand towards the podium, stared at Xu Chuan and said.

The corners of Xu Chuan's mouth twitched, probably understanding that this was Xu Cheng's dissatisfaction, and his dissatisfaction with running to participate in the competition.

But seriously, this problem, ordinary high school students, even if they have the ability to enter the national training team, may not be able to solve it.

The difficulty is almost the same as IPHO, and when you put it on IPHO, it almost belongs to the type of penultimate question.

This question is tested by Bose Einstein condensation, and the whole question has three small parts, the first part is not very difficult, and it can be solved with a certain physical foundation.

However, the difficulty of the second and third small parts rises in a straight line, comparable to riding a rocket, whether it is to find the square root rate according to the average kinetic energy of the atom, or to find the momentum and then find the de Broglie wavelength, the difficulty is not something that ordinary high school students can do.

The difficulty of finding the particle spacing in the third step is even higher.

If the first question is 1+2=3, then the difficulty of the second and third questions soars directly to proving 1+2=3.

Compared with the mathematical competition problem, the amount of calculation in this problem is not large, but the requirements for the logical ability and application ability of the solver are very high.

But this is the ability to learn 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, and the difficulty of physics lies in the application of knowledge and methods.

.......