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问题 计算题

（10分）有一种质谱仪的工作原理图如图所示。静电分析器是四分之一圆弧的管腔，内有沿圆弧半径方向指向圆心O1的电场，且与圆心O1等距各点的电场强度大小相等。磁分析器中以O2为圆心、圆心角为90°的扇形区域内，分布着方向垂直于纸面的匀强磁场，其左边界与静电分析器的右边界平行。由离子源发出一个质量为m、电荷量为q的正离子（初速度为零，重力不计），经加速电场加速后，从M点沿垂直于该点的电场方向进入静电分析器，在静电分析器中，离子沿半径为R的四分之一圆弧做匀速圆周运动，并从N点射出静电分析器。而后离子由P点射入磁分析器中，最后离子沿垂直于磁分析器下边界的方向从Q点射出，并进入收集器。已知加速电场的电压为U，磁分析器中磁场的磁感应强度大小为B。

（1）请判断磁分析器中磁场的方向；

（2）求静电分析器中离子运动轨迹处电场强度E的大小；

（3）求磁分析器中Q点与圆心O2的距离d。

答案

（1）垂直纸面向外（2） （3）

题目分析：（1）带正电的粒子进磁场的速度水平向右，要从下边界Q射出，P点的洛伦兹力必须竖直向下，根据洛伦兹力左手定则判断磁场方向垂直纸面向外。

（2）设离子进入静电分析器时的速度为v，离子在加速电场中加速，

根据动能定理 有       ①  

离子在静电分析器中做匀速圆周运动，指向圆心O1的电场力为向心力，有    ② 

由①②解得     ③

（3）离子在磁分析器中做匀速圆周运动，圆心为O2，根据牛顿第二定律 有

            ④ 

由题意可知，水平向右进入磁场，竖直向下离开磁场，根据几何关系可得圆周运动的轨道半径             ⑤ 

由①④⑤式解得       ⑥

阅读理解
阅读理解。
     A new study suggests that the more teenagers watch television, the more likely they are to develop
depression (抑郁症) as young adults.
     The researchers used a national long-term survey of healthy young teenagers of about 13-16 to find
out the relationship between media (媒体) use and depression. They based their findings on more than
4000 young teenagers who were not depressed when the survey began in 1995.
    As part of the survey, the young people were asked how many hours of television or videos they
watched daily. They were also asked how often they played computer games and listened to the radio.
Here was the result. The young people spent five and a half hours a day using media and more than 2
hours of that was spent watching TV.
    Seven years later, in 2001, more than 7% of the young people had signs of depression. The average
age at that time was 21. Brian Primack at the University of Pittsburgh medical school was the lead author
of the new study. He says every extra hour of television meant an 8% increase in the chances of developing
signs of depression.
     The researchers say they did not find any such relationship with the use of other media such as movies,
video games or radio. But the study did find that young men were more likely than young women to develop
depression given the same amount of media use.
     Doctor Primack says the study did not find out if watching TV causes depression directly. But one
possibility, he says, is that it may take time away from activities that could help prevent depression, like
sports and social activities. It might also prevent a person from sleeping well, he says, and that could have
an influence.
     The study was just published in the Archives of General Psychiatry.
     In December, the journal Social Indicators Research published a study of activities that help lead to happy
lives. Researchers from the University of Maryland found that people who describe themselves as happy
spend less time watching television than unhappy people. The study found that happy people are more likely
to be socially active, to read, attend social services and to vote.
Process of the studyDetails
The purpose of the research To find out 1_______ between media
use and depression.
At the beginning of the research2_______ was made among over 4000 young
people who were not depressed.
The result of the survey These young people spent five and a half hours a
day in using media and they spent over 2 hours or
that 3_______
Seven years laterResearchers found 7% of the young people had a
sign of depression. Every extra hour of watching TV
meant an 8% increase in the chances of developing signs
of depression.
Results of the study1. Watching TV might have 4_______ and it may take time
     away fromactivities and sports.
2. Young men get more chance than young women
    to develop depression.
3. The reason some people get depression is that 5_______
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填空题

写出下列反应的化学方程式,并在括号内注明反应的基本类型。

（1）铁在氧气中燃烧____________ 。（    ）        

（2）加热氯酸钾与二氧化锰混合物制氧气________________。（    ）

（3）通电分解水____________________。（     ）

（4）氢气在氧气中燃烧___________________。（    ）

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