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问题 计算题

如图所示为真空示波管的示意图。电子从灯丝K发出（初速度不计），经灯丝与A板间的加速电压U1加速，从A板中心孔沿中心线KO射出，然后进入由两块平行金属板M、N形成的偏转电场中（偏转电场可视为匀强电场）。电子进入偏转电场时的速度与电场方向垂直，电子经过偏转电场后打在荧光屏上。已知M、N两板间的距离为d，板长为L1，电子质量为m，电荷量为e。求：

（1）电子在偏转电场中运动的时间；

（2）为了使电子能从偏转电场中射出，则M、N两板间所加恒定电压应满足什么条件？

答案

解：（1）设电场号经电压U1，回速度后的速度为v0，根据动能定理得

  ①

电子穿过偏转电场时，水平方向匀速运动由

②  

由①②得 ③  

（2）电子进入偏转电场后，电子的加速度为a，侧移量为y，设偏转电压为U2

则有： ④

又 ⑤

电子不打到板 ⑥

由③④⑤⑥得

改错题

As a child, I took the school as fairly beautiful garden. I went                小题1:_______

straight to school happily and excitedly with a lovely school bag. How         

小题2:_______

time flying! Now I’m studying at a senior middle school. I have a lot of             

小题3: _______

homework to do every day. Some of my classmates are often stay up late            

小题4:_______

and don’t get enough sleep so that they can’t focus at their lessons.                     

小题5:_______

But I enjoy putting my heart into listening to the teachers. Get up                 

小题6:_______

early and reading aloud helps me memorize what I had learned easily.                  

小题7:_______

During breaks between class, I often relax myself. I’m certain                            

小题8:_______

I ’ll never forget the wonderful time at school.
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问答题 简答题

打溜子，用土家语又叫着什么？
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