如图所示是示波管的原理示意图。电子从灯丝发射出来的经电压为U1的电场加速后,通过

题型:问答题

问题:

如图所示是示波管的原理示意图。电子从灯丝发射出来的经电压为U1的电场加速后,通过加速极板A上的小孔O1射出,沿中心线O1O2进入MN间的偏转电场,O1O2与偏转电场方向垂直,偏转电场的电压为U2,经过偏转电场的右端P1点离开偏转电场,然后打在垂直O1O2放置的荧光屏上的P2点。已知平行金属极板MN间的距离为d,极板长度为L,极板的右端与荧光屏之间的距离为L′。不计电子之间的相互作用力及其所受的重力,且电子离开灯丝的初速度可忽略不计。(电子的质量为m,电量为e)求:

(1)电子通过小孔O1时的速度大小V0

(2)电子在偏转电场中的加速度大小a;

(3)电子通过P1点时偏离中心线O1O2的距离y;

(4)电子离开偏转电场时的动能Ek

(5)若O1O2的延长线交于荧光屏上O3点,而P2点到O3点的距离称为偏转距离Y(单位偏转电压引起的偏转距离,即Y/U2称为示波管的灵敏度),求该示波管的灵敏度。

考点:带电粒子在电场中的加速
题型:问答题

Have you been back to the place    your ancestors lived, worked, studied and

played?  Robert Qian , a Chinese Canadian, already has. Now in China, he has found

that his family   like a tall tree with long roots.

Robert is just one young overseas Chinese who    to visit his ancestors’

homeland, as part of the In Search of Roots summer camp program. The program      by the local government of Guangdong Province. This program started in 1980, and so far has brought    overseas Chinese students to China to look for their families’ roots. The young people are usually between 16 and 25 years old. Most, like Robert, can hardly   any Chinese and have never been to China before.

The students mainly visit parts of Guangdong Province in southern China. During the     camp, they study Chinese culture, see changes that have happened in that area, and visit interesting sights. Going to their ancestors’ village is often        part of the trip.The students feel that they are part of the village, and    village life. They drink from the village well, go for walks    the countryside, and watch the villagers do their daily activities.

Cathy Qian, a young American student, had this to say, “    In Search of Roots, I am beginning to understand my Chinese roots and who I am. It has been a great trip, and I have     memories of China to take with me .”

The program leaders believe      in the program and say that the purpose of it is to give young overseas Chinese the chance to learn more about  . “I’ve really enjoyed the trip so far,” says Robert.“This has been a big step for me, and I’m looking forward to   more about my roots during my time here.

小题1:

A.where

B.what

C.that

D.which

小题2:

A.where

B.was

C.is

D.are

小题3:

A.has come

B.have come

C.will come

D.are coming

小题4:

A.can be organized

B.is organizing

C.organizes

D.is organized

小题5:

A.thousands

B.thousands of

C.thousand

D.thousand of

小题6:

A.say

B.speak

C.tell

D.talk

小题7:

A.two-week

B.two weeks

C.two-weeks

D.two week

小题8:

A.the most surprising

B.the most boring

C.more exciting

D.the most exciting

小题9:

A.experience

B.enjoy

C.change

D.worry

小题10:

A.though

B.across

C.cross

D.through

小题11:

A.Thanks for

B.Thanks to

C.Thanks

D.Thanks a lot

小题12:

A.much too

B.too much

C.too many

D.so much

小题13:

A.strongly

B.hardly

C.hard

D.heavily

小题14:

A.himself

B.herself

C.them

D.themselves

小题15:

A.finding out

B.find out

C.helping out

D.help out

题型:问答题
大于
1
5
而小于
3
5
的最简分数只有
2
5
.______.(判断对错)
题型:问答题

经典物理学的奠基人是______,相对论的创立者是______.

题型:问答题

客观事物引起人的情绪和情感的中介是( )

A.动机
B.兴趣
C.信念
D.需要

题型:问答题

城市生态规划的目的是利用城市的各种自然环境信息、人口与社会文化经济信息,根据城市土地利用生态适宜度的原则,为城市( )决策提供可供选择的方案。

A.发展方向的

B.土地利用

C.开发区设立

D.人口规模

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