把一段长度为1m的直导线，沿着某一固定的方向放置在磁感应强度为_爱下问搜题

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问题选择题

把一段长度为1m的直导线，沿着某一固定的方向放置在磁感应强度为B的匀强磁场中，当只导线通电电流为5A时，测得该直导线受到的安培力的大小F=0.5N，那么，仅仅根据以上数据，可以判断该匀强磁场的磁感应强度B的大小是（　　）

A．B＜0.1T

B．B=0.1T

C．B≤0.1T

D．B≥0.1T

答案

由公式F=BILsinθ，可知当夹角为90°时磁感应强度最小，此时：B=

F

IL

=0.1T

因此B≥0.1T，故ABC错误，D正确．

故选D．

完形填空

完形填空阅读短文，从每题所给选项中选出可以填入空白处的最佳选项（共15分；每空1分，满分15分）
The students in Shanghai No. 3 Girls High School have a flower-arrangement (插花) lesson every week. The course is the first of its kind among middle schools in Shanghai. It helps the students to enjoy the   46  of flowers better. That’s why the course has become very popular   47  the students.
The teachers of the course are all specially trained(专门地培训). They are   48   at this art and work hard at passing on the skill   49  students. So far, many students in the school have   50  a lot of prizes in this field. In order to further   51  the students’ skills, the teachers usually play   52  while students are arranging flowers. Students are   53  with the music, and they   54  more good ideas for flower-arrangement.
Besides, the teachers   55  teach the students other skills at the   56  time. For example, they ask the students to   57  compositions(作文) about flowers. In this way, students not only   58   art education but also improve(提高) their writing skills.
Several months ago, some foreign teachers   59  the school. When they saw common flowers become more lively and meaningful, they were amazed and interested. They made videos and would play them in class for their own   60  after they returned home.

单项选择题

欲进行胃癌危险因素的病例对照研究，下列不能作为对照的是

A．支气管炎病人

B．胃病病人

C．意外损伤病人

D．肠道传染病病人

E．眼病病人