问题 计算题

如图所示为两组平行板金属板,一组竖直放置,一组水平放置,今有一质量为m、电量为q的电子静止在竖直放置的平行金属板的A点,经电压U0加速后通过B点进入两板间距为d、电压为U的水平放置的平行金属板间,若电子从两块水平平行板的正中间射入,且最后电子刚好能从右侧的两块平行金属板穿出,A、B分别为两块竖直板的中点,求:

(1)电子通过B点时的速度大小;

(2)右侧平行金属板的长度;

(3)电子穿出右侧平行金属板时的动能。

答案

(1) (2) (3)

题目分析:(1)根据动能定理可得

解得电子到B点的速度为    5分

(2)电子进入右侧平行板后,在水平方向上做匀速运动,在竖直方向上做匀加速直线运动,故

在水平方向上有:

在竖直方向上有:

联立可得               5分

(3)整个过程中电场力做功为,

所以根据动能定理可得   5分

点评:关键是分析质子的分析情况和运动情况.在偏转电场中质子做类平抛运动,采用运动的分解方法研究.

阅读理解

阅读理解。

     That our students rarely get the opportunity to use their imagination was an open secret among Chinese

people. Now,a global survey has brought it to the notice of the rest of the world. 

     The survey covering 21 countries, conducted by International Educational Progress Evaluation

Organization, showed Chinese students excelled at math, beating their peers from other countries. But when

it came to using their imagination, they were tied for the last place. And in creativity, they were fifth from

the bottom.

     The survey results are not shocking, given the way our children are taught in schools and at home. But

they are a severe reminder to our educators and parents to improve their ways.

     Chinese students rarely get the time or chance to use their imagination. Right from the day they enter

school they are pushed into a culture of exams and more exams.

     Teachers and parents teach them that education is all about passing these exams with flying colors. And

to pass those exams, they are made to learn by fixed standard answers. Teachers dare not encourage students

to think outside the box. Teachers don't like students questioning them, killing the curiosity of the young

minds. For children, there's hardly any room for bright ideas either in class or at home.

     Israel shares the values of education with China. But there is a world of difference between the way Israeli

parents treat their children and we do. Israeli parents do not mollycoddle their children. Instead, they

encourage them to learn how to live independently. In contrast, Chinese parents go to extremes, allowing their

children to do whatever they like to do and punishing them severely the next for committing a "mistake".

     The global study should make us swing into action and help our students to throw open their young minds

to imagination and creativity. It is time our education officials and educators asked themselves what they

should do to let our children's imagination and creativity blossom.

1. Based on the text, the creativity of the Chinese students ranks _____ among the 21 countries.

A. the 5th

B. the 17th

C. the 2lst

D. the 1st

2. Why is the imagination of the Chinese students so poor?

A. Their parents often improve their educational ways.

B. They are thought to be lacking in curiosity.

C. Their teachers are afraid of being questioned.

D. They are not encouraged to imagine both at home and in class.

3. What does the underlined word "mollycoddle" probably mean in Paragraph 6?

A. spoil

B. motivate

C. appreciate

D. scold

4. It can be learned from the text Israeli parents _____.

A. lay much more emphasis on education than Chinese ones

B. allow their children to live in whatever way they like

C. focus more attention on developing their children's living ability

D. encourage their children to commit mistakes in lives

5. Israel is introduced in the text mainly _____.

A. to enrich the content of the text

B. to support and advocate Israel education

C. to illustrate the disadvantages of Chinese education

D. to criticize the wrong behavior of Chinese parents

单项选择题