Today's two-hour make-up class time has become unusually long, and Qian Xiaoxian's brain has been in a state of dissociation.

Gao Jian's words that made her blush and heartbeat kept ringing in her ears.

She also vaguely felt that danger was approaching, no wonder there was no such thing as a free lunch in the world, the truth.

Qian Xiaoxian even stubbornly thought that he had been so good to himself recently just to achieve his goal.

Thinking of what he said just now, Qian Xiaoxian suddenly felt suspicious of Gao Jian, he actually went to confirm his innocence with Lin Wei, she felt that he didn't fully believe Lin Wei's words, so he was desperately trying to be good to himself recently, just to verify what he just said.

Thinking of his words, Qian Xiaoxian felt uncomfortable.

Although she was not worried about her integrity, she thought that Gao Jian wanted to ...... with her with such a purpose

God, why did she suddenly feel humiliated?

While I was thinking about it, my phone vibrated a few times.

Qian Xiaoxian took out her mobile phone and looked at it, it was a WeChat message from Gao Jian.

"Baby, I'm waiting for you at the door of the tutoring class, I'm so bored. ”

Qian Xiaoxian was taken aback by his sudden numb name, she hurriedly put her phone under the table and said, "There is still an hour, what are you waiting here for a long time? Aren't you very busy?"

"The recent project of the tourist park is on the right track, and the heads of various departments are already competent, so I want to treat myself, and I will only accompany you today. ”

Oh my God, Gao Jian really had another convulsion today.

"Baby, it's so hard to wait. ”

"Are you out of class at four?"

"Give me a call when you come out. ”

The mobile phone kept vibrating, and Qian Xiaoxian hurriedly swept the two students next to her as reflexively, and the boy sitting on the right turned his face to look at her.

She hurriedly covered the screen of her phone with her hand.

She used her spare eyes to see the boy turn his face, and then she turned on the phone screen to send a message to Gao Jian, it's all your fault, I didn't understand what the teacher said just now!

"Send me here, I'll tell you!"

On the podium, the tutor was talking about a typical example question in the first volume of the country.

This type of problem is exactly what she finds difficult to "the motion of charged particles in a magnetic field".

In this regard, Qian Xiaoxian was originally weak, and she couldn't concentrate her energy just now, so she didn't have a clue at all.

She saw that Gao Jian said so easily, she thought to herself, why not send him the question and beat his arrogance in front of her, she felt that Gao Jian had graduated for so many years, maybe he had forgotten this kind of question!

Yes, it's hard for him!

Qian Xiaoxian sent a message: "Are you sure you will do it?"

"Sure!"

"What if you can't do it?"

"If I can't do it, I'll do whatever you ask me to do today. If you do it, you will do whatever I tell you to do!"

Qian Xiaoxian hesitated for a moment, and Gao Jian's news came again: "What's wrong?"

Gao Jian's idea really worried her, because now Gao Jian's words and deeds are starting to be abnormal again, and she can't get into his trap!

"When the time comes to think about it, you hurry up and send the question. ”

Qian Xiaoxian looked at the dense numbers on the blackboard, and thought, now that he is so busy every day, can he still make such a difficult question?

She took out her phone and quietly took a picture of the blackboard.

Then she added, "There's a time limit! Ten minutes." ”

"Okay. "Gao Jian replied in seconds.

Qian Xiaoxian stared at the question in the chat window, imagining Gao Jian's thinking, and she couldn't help but smile quietly.

This question is really not ordinarily difficult, especially the third question, the teacher said that it was the finale.

Qian Xiaoxian was not in the mood to listen to what the teacher said again, and she also stared at this question at the same time, so it was really fresh to be at the same frequency with Gao Jian......

The question goes like this-

As shown in Figure 2, there is a uniform magnetic field perpendicular to the xOy plane in the region of 0≤x≤a, and the magnitude of the magnetic induction intensity is B. At t=0, a particle source located at the origin of coordinates emits a large number of charged particles of the same kind in the xOy plane, and the initial velocity of all particles is the same, and the angle between the direction and the positive direction of the y-axis is distributed in the range of 0°~180°. It is known that the particles emitted in the positive direction of the y-axis leave the magnetic field just from the point P(a,a) on the magnetic field boundary at t=t0. Beg:

The first question: (1) the radius R of the circular motion of the particle in the magnetic field and the specific charge q/m of the particle;

The second question: (2) the range of the angle between the direction of the initial velocity and the positive direction of the y-axis of the particle that is still in the magnetic field at this moment;

Question 3: (3) The time from the emission of the particles to the time when all the particles leave the magnetic field.

Unexpectedly, as soon as Qian Xiaoxian finished reading the question, Gao Jian's voice came over, because it was not suitable for listening in the classroom, she had to convert the voice into text-

This kind of problem first finds the radius of the circular motion of the charged particles in the magnetic field, first let the particle motion speed be v and the radius is r, look at the figure, know from the geometric relationship r = 2 root number 3/3 * a, after finding the radius, by qvB=mv*v/r, period T=2 r/v, and then calculate the time of movement in the magnetic field, and then find q/m, so, easy!

Qian Xiaoxian was stunned for a moment, she quickly looked up at the side of the blackboard, and the analysis written by the teacher when she explained turned out to be similar to Gao Jian's.

At this time, Gao Jian's news came again-

According to the conditions given in the original question, the particles that are still in the magnetic field at the same time are at the same distance from point O. The particles that are still in the magnetic field at time t0 should be located on an arc with point O as the center and OP as the radius.

Let the initial velocities of the particles at P, M, and N be vP, vM, and vN, respectively. From the symmetry, it can be seen that the angles between vP and OP, vM and OM, and vN and ON are all π/3. Let the angles between vM, vN and the positive direction of the y-axis be θM and θN respectively, and the geometric relation θM=θN=(8), for all particles that are still in the magnetic field at this time, the angle θ range between their initial velocity and the positive direction of the y-axis should be pie/3 to 2/it or leave it?

Qian Xiaoxian didn't expect him to send an answer so quickly, and she didn't want to confirm whether what he did was right or not, but sent a message saying: "The teacher said that the first question is given for nothing, the first and second questions are not difficult for most people, and the teacher said that the third question can be done to see the strength!"

Gao Jian immediately sent a message and said: "If it's in the exam room, I advise you not to read the third question, because the comprehensive is only 2.5 hours, 18 pages, you can't finish it at all, you just give up this kind of finale question, so I don't need to tell you this, and you don't need to waste time and energy on this kind of question." ”

Qian Xiaoxian sent a message saying: "You quibble, it must be an excuse that you won't do!"

"Qian Xiaoxian, if I make it, you and I will move to a new house tomorrow!OK?"

After reading Gao Jian's news, Qian Xiaoxian's heart beat faster, that's it, the fox's tail is exposed!

He just wants to set a trap for himself!

couldn't let him succeed, Qian Xiaoxian hurriedly sent a message: "Forget it, you are right, I should give up the third question, you don't want to do it again......"

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