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问题 选择题

如图所示，在匀强磁场中，AB为粗细均匀的铁芯，C为AB的中点．输出电压恒为U的电源接A、B两端时，铁芯受到的安培力为F；若接A、C两端时，铁芯受到的安培力为（　　）

A．2F

B．F

C．

F
2

D．

F
4

答案

根据安培力大小公式可知，输出电压恒为U的电源接A、B两端时，铁芯受到的安培力：F=B

U
R
L，

接A、C两端时，铁芯受到的安培力，则有：：F′=B

U
R
2
×
L
2
=F，故B正确，ACD错误；

故选：B

单项选择题 A1型题

下列哪项不是预防职业性汞中毒的措施（）

A.以气动仪表代替汞仪表

B.改善作业环境条件，使空气中汞的浓度不超过0.01mg／m

C.车间温度控制在18℃以下

D.戴防毒口罩

E.改善作业环境条件，使空气中汞的浓度不超过0.05mg／m
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单项选择题

Traditional structured analysis techniques focus upon the flow of (71) within a system. Object - oriented analysis emphasizes the building of real - world models. It examines requirements from the perspective of the classes and objects found in the vocabulary of the (72) domain.

Traditional system design method emphasizes the proper and effective structure of a complex system. Object -oriented design method encompasses the process of object -oriented decomposition and a (73) for depicting both logical and physical as well as static and dynamic models of the system under design.

Object - oriented programming is a method of implementation in which programs are organized as cooperative collections of objects, each of which represents an (74) of some class, and whose classes are all members of a hierarchy of classes united via (75) relationships.

72（）

A．problem

B．solution

C．data

D．program
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