问题 问答题

)电阻r=0.5Ω的金属导体PQ, 在两根相互平行的金属滑轨上滑动. 金属滑轨的左端接定值电阻R=1.5Ω, 平行滑轨间距离为L="0.2m," 垂直滑轨平面加匀强磁场, 磁场感应强度B="0.1T," 方向如图所示, 当金属导体PQ沿滑轨运动时, 电阻R上流过0.1A的电流, 方向自下而上. 求此时PQ的运动速度大小和方向.

答案

10m/s   ;速度的方向向左

ε="I(R+r)" =0.1(1.5+0.5)V=0.2V

ε="BLv   "  速度的方向向左

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阅读理解

     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.

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