Xueba, I beg you to go and escort him quickly!

"It's enough to show how much the principal attaches importance to you!"

Xu Heng also became serious, "I understand, Dean Nie!"

"However, you really don't need to be so emphatic! I understand everything."

Dean Nie's face darkened instantly, not knowing what to say.

How could Xu Heng not know that the headmaster of one of the top schools in China came here to see him in person.

Look light!

It actually means a lot!

Although after meeting, there were only a few words, but this is the excellence of this principal.

Superficially!

Although it is a superficial point, this point can cause "ripples" on "the entire lake"!

The high state of being a person and doing things!

Xu Heng understood and smiled slightly.

In order to put aside the topic, Dean Nie sighed, "Hey... This is a pain for Professor Fang."

Xu Heng, "What do you mean? Dean Nie."

Dean Nie smiled, "Professor Fang wanted to discuss the knowledge points of physics and the postgraduate entrance examination with you, but now he is with the principal."

"It's the principal after all! Can you let him have his own car?"

Xu Heng smiled.

I know everything!

When he arrived at the service area, Fang Zhonggui couldn't wait to come to Xu Heng's side.

He even went in and out of the bathroom with Xu Heng, discussing topics all the time.

In the end, the two settled on a question.

A long rod with a rectangular cross-section whose side lengths are a, b, and c (abc) is made of semiconductor indium antimonide.A current I flows in the rod parallel to side a.The rod is placed in an external magnetic field B parallel to side c, and the magnetic field generated by the current I can be ignored.The carriers of this current are electrons.In the presence of only an electric field, the average velocity of electrons in a semiconductor is v = μE, where μ is the mobility.If a magnetic field is also present, the total electric field is no longer parallel to the current, a phenomenon known as the Hall effect.

(a) Determine the magnitude and direction of the total electric field in the rod that produces the above current.

(b) Calculate the potential difference between two opposite points on the two surfaces sandwiching side b.

(c) If both the current and the magnetic field are alternating, and are respectively I=I0sinωt, B=B0sin(ωt+φ).Write down the analytical expression for the DC component of the potential difference in case b).

(d) Using the results of c), design an electronic circuit that can measure the power consumed by electronic equipment connected to the AC grid, and give an explanation.

Using the following data: The electron mobility in indium antimonide is 7.8m2/V·s

The electron density in indium antimonide is 2.5×10 (22th power) m-3

I=1.0AB=1.0Tb=1.0cmc=1.0mme=1.6×10（－19次方）C

Fang Zhonggui looked at the question and patted his thigh.

"it is good!"

"it is good!"

"it is good!"

Three good days in a row seemed to give him courage!

Let him muster up the courage to stay away from the principal and sit in a car with Xu Heng.

Fang Zhonggui, "Dean Nie, why don't you go and accompany the principal?"

Dean Nie is also unwilling.

The two looked at each other and smiled.

"Then leave the principal alone!"

"I think he'll understand us!"

When the car left the service area, the principal asked the driver why he didn't see Professor Fang.

But the driver said, "Principal, I watched Professor Fang get into the car in front."

Principal, "%￥#@￥%..."

"Hey... okay! That's it..."

The driver was shocked.

God!

This classmate Xu Heng actually made Dean Nie and Professor Fang abandon the principal directly.

!!!

With the car on the high speed.

Dean Nie and Fang Zhonggui couldn't wait to discuss related issues with Xu Heng.

Fang Zhonggui prepared a notebook, which he brought specially.

"Student Xu Heng, help me take a look. I was inspired by your monthly examination paper for this question."

Xu Heng took a closer look.

The crystal lattice of Nacl is composed of a cubic unit cell with a side length of 5.6*10 (-8 power), which is a face-centered cubic lattice.

The atomic weight of sodium is 23, the atomic weight of chlorine is 35.5, and the density of Nacl is 2.22g/cm3.

Calculate the mass of a hydrogen atom.

This question is very cute!

Very interesting question!

Xu Heng took a picture of it on the spot and posted the question to the group.

"Professor Fang, this question cannot be used for the postgraduate entrance examination! The category is too low! So let me take advantage of it! I posted it in the group and did it for everyone."

In the group!

Xu Heng updated the question bank again.

Get everyone excited...  

But when they look at the question.

"Chemistry problem?"

"No...it's not a chemistry problem! But...is this a physics problem? Or, a math problem?"

"???"

"Don't worry about it, let's do it!"

"I'm going... There's no way to start?"

"How to do it?"

"???"

"What the hell?"

Just when everyone was wondering, Xu Heng posted a picture again.

Only then did everyone know how to start.

Xu Heng put away his phone and smiled at Fang Zhonggui and Dean Nie.

Fang Zhonggui had a weird expression on his face, "Student Xu Heng, you really don't want to lose money to outsiders!"

"Student Xu Heng, you're going to answer one of my questions!"

Xu Heng waved his hand, "Return it! Repay it! Professor Fang, give me a pen and paper."

Professor Fang couldn't wait.

He prepared a new pen and paper and handed it to Xu Heng.

As for his own notebooks for taking notes and writing out questions.

He silently put it away.

He felt that the questions he posed were not hot enough.

Xu Heng's performance just now proved this point.

The questions I asked were either too old-fashioned or not difficult enough.

Compared with Xu Heng, the difference is too much!

Xu Heng was silent for two or three minutes, writing and drawing on paper.

When Fang Zhonggui came back to his senses.

Dean Nie looked at Xu Heng's densely written words on the paper, and was already dumbfounded.

topic:

What is being discussed and studied now is a certain space research program, two launch schemes for launching spacecraft to the outside of the solar system.The first option is to launch the spacecraft at a velocity high enough that it escapes directly out of the solar system.The second option is to bring the spacecraft close to an outer planet and, with its help, change the direction of the spacecraft's motion to achieve the speed necessary to escape the solar system.Assume that the spacecraft moves only in the gravitational field of the sun or planets.So whether it moves in the gravitational field of the sun or in the gravitational field of the planet, it depends on which field is stronger at this point.

(a) Determine the minimum velocity va relative to the earth and its direction necessary to launch the spacecraft according to Scheme 1.

(b) Suppose the spacecraft has been launched in the direction determined in (a), but with another velocity vb relative to the earth.Find the velocity of the spacecraft when it crosses the orbit of Mars, that is, the parallel and perpendicular components relative to this orbit.When the spacecraft crosses the orbit of Mars, Mars is not near this node.

(c) Assuming that the spacecraft enters the gravitational field of Mars, try to find the minimum speed required to launch the spacecraft from the earth to escape the solar system.

Tip: From the result (a), we can know the magnitude and direction of the optimal speed for the spaceship to escape from the solar system after breaking away from the gravitational field of Mars (it is not necessary to consider the precise position of Mars when passing through the orbit of Mars).Find the relationship between this optimal velocity and the velocity component of the spacecraft before entering the gravitational field of Mars, which is the velocity component you determined in (b).What about the energy conservation of the spaceship?

(d) Estimate the maximum percentage of possible energy savings for the second alternative over the first.Note: Assume that all the planets revolve around the sun in circular orbits in the same plane and in the same direction.Neglect air resistance, the rotation of the Earth, and the energy expended to escape from the Earth's gravitational field.Data: The speed of the earth revolving around the sun is 30km/s, the ratio of the distance from the earth to the sun and the distance from Mars to the sun is 2/3.

Compared with the [-] provincial joint examinations.

Xu Heng's requirements for postgraduate entrance examination questions are different.

After writing down the question, Xu Heng gave the answer by the way below.

Let Va be the launching velocity relative to the earth, VE be the earth velocity, and θ be the angle between VE and Va.

The total energy of the spacecraft in the solar system is...

……

Among them, m is the mass of the spacecraft, V is the velocity relative to the solar system, M is the mass of the sun, and ME is the mass of the earth.

Necessary conditions for a spacecraft to escape the solar system...

……

Vs2-VM2-2VMV〃+V2〃+V2⊥=VM2-2VMV

V2+2VM2-2VE2≥3VM2-2VM2

……

The maximum percentage of energy saved is 80%

……

Under the bewildered expressions of Dean Nie and Fang Zhonggui, Xu Heng slowly put down his pen.

"I think it takes half an hour for you to do this question. For you, this half hour is a waste of time, so I will give the answer directly. Do you have any opinions?"

But Dean Nie and Fang Zhonggui's expressions didn't mean that at all.

Dean Nie, "!!!"

Fang Zhonggui, "!!!"

Hemp egg!

Who said there is no opinion!

Student Xu Heng, you...

PS: Kneel for all support!I wish you all a Happy New Year! .