问题 选择题

如图所示,在两等量同种点电荷的电场中,MN为两电荷连线的中垂线,B是直线AC与MN的交点,且A与C关于MN对称,D点是两电荷连线上的一点.下列判断正确的是(  )

A.B点场强一定大于D点场强

B.B、D两点的场强可能相同

C.试探电荷+q在A、C两点受到的电场力大小可能不相等

D.试探电荷+q在A、C两点受到的电场力大小相等

答案

解;

A、在两等量同种电荷连线上,中点的电场强度最小;在两等量同种电荷连线的中垂线上,中点的电场强度最小;由于B、D两点处电场线的疏密不能确定,所以不能判断出B点场强与D点场强的大小关系.故A错误.

B、B点的场强方向向上,D点场强方向向右,所以两点的场强不可能相同,故B错误;

C、D、因两等量同种电荷的电场具有对称性,所以A、C两点的场强大小相等,试探电荷+q在A、C两点受到的电场力大小相等,故C错误,D正确.

故选:D.

阅读理解

阅读理解。

     "Confidence" is probably one of the most noticeable traits (品质) in the Americans. They show

confidence in the way they talk, the way they smile, the way they dress and the way they walk.

Living and competing with all these confident American students, I find it extremely important to

be confident as an international student and instructor. As a student, being confident means you

should never hesitate to raise your hand whenever a question or a point comes to your mind.

Don't mind if it sounds simple or silly. Otherwise you will never get a chance to speak in class at

all. What's worse, the professors may think you are not prepared for the discussion or you do not

have your own opinion on the issue-this is the last comment any graduate would like to receive.

     Being confident for me as a foreign instructor means calmly asking the student to repeat what

he or she has said if I did not get it. Pretending to understand what you actually did not may just

bring yourself embarrassment or even disgrace. But the time I most need to be confident is when

my students come to my office and bargain about the grades I have given for their speeches.

(The course I'm teaching here is Public speaking). Modesty is a trait highly valued in China, but it

won't be of much help here if you want to survive and succeed in a good American graduate

program.

1. To compete with American students it's very important to      .

A. be quite confident

B. be polite and friendly

C. have more discussions with them

D. understand what they think about

2. A professor will have the worst opinion of a student who      .

A. gives a silly or simple answer

B. tries to seize any chance to speak in class

C. shows no interest in the course

D. is considered to have no opinion of his own

3. The author is most likely to feel embarrassed if       .

A. he asks a student to repeat what he has said

B. the students bargain with him

C. he pretends to know what he doesn't

D. he has to give a speech

4. We learn from the second paragraph that       .

A .we should also remain modest in America

B. modesty doesn't help you much in America

C. Americans also like modest people

D. modesty can help you through an American graduate program

5. What can we infer from the passage?

A. American students are ready to accept the grades from the teacher.

B. The writer teaches in Europe for a living.

C. Students are encouraged to present simple questions.          

D. One's ignorance will give away in time.

单项选择题 A1型题