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【题目】如图所示,把一重力不计的通电直导线AB水平放在蹄形磁铁磁极的正上方,导线可以在空间自由运动,当导线通以图示方向电流I时,导线的运动情况是从上往下看)(

A顺时针方向转动,同时下降

B顺时针方向转动,同时上升

C逆时针方向转动,同时下降

D逆时针方向转动,同时上升

【答案】C

【解析】如图所示,将导线AB分成左、中、右三部分中间一段开始时电流方向与磁场方向一致,不受力;左端一段所在处的磁场方向斜向上,根据左手定则其受力方向向外;右端一段所在处的磁场方向斜向下,受力方向向里当转过一定角度时,中间一段电流不再与磁场方向平行,由左手定则可知其受力方向向下,所以从上往下看导线将一边逆时针方向转动,一边向下运动,C正确

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