试题与答案

如图所示，一块通电的铜板放在磁场中，板面垂直于磁场，板内通有如图所示方向的电流，

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题型：多选题

题目：

如图所示，一块通电的铜板放在磁场中，板面垂直于磁场，板内通有如图所示方向的电流，a、b是铜板左、右边缘的两点，则（　　）

A．电势φa＞φb

B．电势φa＜φb

C．电流增大时，|φa-φb|不变

D．其他条件不变，只将铜板改为中性NaCl水溶液时，φa=φb

答案：

A、电流方向竖直向上，则电子从上往下流，根据左手定则，电子向左侧偏转，则左侧聚集较多的电子，右侧失去电子带正电，所以b点的电势高于a点的电势．故A错误，B正确．

C、仅电流增大时，电子的运动速度增加，受到的洛伦兹力增大，根据qvB=q

U
d
，知U=Bdv，则电势差增大，即|Ua-Ub|增大．故C错误．

D、其他条件不变，只将铜板改为中性NaCl水溶液时，根据左手定则知，正负离子都向左偏，不产生霍尔效应，a、b电势相等．故D正确．

故选：BD．

考点：电磁感应现象的综合应用
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