问题 选择题
如图所示,两个端面半径同为R的圆柱形铁芯同轴水平放置,相对的端面之间有一缝隙,铁芯上绕导线并与电源连接,在缝隙中形成一匀强磁场.一铜质细直棒ab水平置于缝隙中,且与圆柱轴线等高、垂直.让铜棒从静止开始自由下落,铜棒下落距离为0.2R时铜棒中电动势大小为E1,下落距离为0.8R时电动势大小为E2.忽略涡流损耗和边缘效应.关于E1、E2的大小和铜棒离开磁场前两端的极性,下列判断正确的是(   )

A.E1>E2,a端为正

B.E1>E2,b端为正

C.E1<E2,a端为正

D.E1<E2,b端为正

答案

答案:D

单项选择题 共用题干题
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     BEIJING-Seven prestigious universities in China announced Sunday that they would begin using the

same independent exam -besides the national one -to test students hoping to gain entrance to them in

2011.

     The seven are Peking University, Beihang University, Beijing Normal University, Nankai University,

Fudan University, Xiamen University and Hong Kong University.

     Students who want to gain entrance to any of the seven universities will only have to sit one

independent exam, according to the joint announcement.

     "This will help lighten tile students' load, otherwise they must take several exams for different

universities,"said the announcement.

    Passing the exam could result in more than one interview chance, giving the students more

opportunities to choose their favorite universities.

     China' s college entrance exam system is undergoing reform as universities aim to select students

based on independent criteria rather than just using the results of the national exam.

     In 2003, Peking University and another 21 universities were allowed to pilot (试用) the reform by

using their own criteria to independently select five percent of their students.

    Now nearly 80 universities across the country have the right to select talented students based on their

own exams.

     Education experts regard universities selecting students according to independent examinations as

conducive (有助的) to better understanding where the students' talents lie.

     Although this may be the case, it has also created problems as students may sit many different exams

as they often apply for a number of universities.

     To relieve students from such pressures, the national education outline (2010-2020) released in July

this year encourages high-level universities to group together to use the same exams.

1. If students want to be admitted to the seven prestigious universities, they can______.

A. only pass the interview.      

B. only take the national exam.

C. only take the independent exam.

D. either take the national exam or the take the independent exam.

2. What's the purpose of students sitting one independent exam to gain entrance to the seven universities?

A. It can reduce students'load to take several exams.

B. The universities will have the same standard to test students.

C. There will be less trouble marking students' test papers.

D. It can avoid fierce competition among these universities.

3. If students pass the independent exam,they will ______.

A. take the national exam.      

B. have one or more interview chances.

C. be admitted to one of the universities.

D. he trained to be adapted to universities life and studies.

4. What is the advantage of universities selecting students according to independent examinations?

A. Students needn't take the national exam.  

B. Students'education cost can be lowered.

C. Students abilities and talents can be better found.

D. It can encourage middle schools to recommend more qualified students.