如图所示，有一电子（电量为e）经电压U0加速后，进入两块间距为d_爱下问搜题

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问题问答题

如图所示，有一电子（电量为e）经电压U₀加速后，进入两块间距为d、电压为U的平行金属板间，

若电子从两板正中间垂直电场方向射入，且正好能穿过电场，求：

（1）电子进入偏转电场时的速度；（2）金属板AB的长度．

答案

（1）设电子被加速后速度大小为v₀，对于电子在加速电场中由动能定理得：

eU_o=

1

2

mv

20

①

所以v₀₌

2eU0

m

②

（2）在偏转电场中，由电子做类平抛运动，设加速度为a，极板长度为L，由于电子恰好射出电场，所以有：

a=

eU

md

③

L=v₀t ④

d

2

=

1

2

at² ⑤

由②③④⑤解得：L=d

2U0

U

所以（1）电子进入偏转电场时的速度为

2eU

0

m

（2）极板的长度为d

2U0

U

填空题

阅读下面短文，按照句子结构的语法性和上下文连贯的要求，在空格处填入一个适当的词或使用

括号中词语的正确形式填空。

Do you feel 1._____ difficult to be happy all the time? Now I'll give you some tips 2._____ how to make

yourself happy. One way is being unselfish because 3._____ (self) is the key factor 4._____ (require) if you

want to get along well with others. By 5._____ (say) being unselfish we mean we should not want everything

our own way or demand the best share of everything. 6._____ way is to look for good points in other people.

You'll find most people pleasant to go with and it will surely make you happy. Third, you can not expect to be

too perfect, 7._____ don't be too unhappy when you make a mistake. Everything will be OK if you try to make

things right. Finally, it is important to remember 8._____ while you are no 9._____ (bad) than others, chances

you have may not be much better. In this case, 10._____ surest way to be happy is to think yourself above

other people.

单项选择题

下列哪项与消化性溃疡的发生无关（）

A.幽门螺杆菌感染

B.吸烟

C.胃窦部壁细胞减少，功能减退

D.正常粘膜屏障被破坏