如图所示，两金属杆AB和CD长均为L，电阻均为R，质量分别为3m和m．用两根质量

发布时间：2017-07-06 14:52 │ 来源：www.tikuol.com

题型：问答题

问题：

如图所示，两金属杆AB和CD长均为L，电阻均为R，质量分别为3m和m．用两根质量和电阻均可忽略的不可伸长的柔软导线将它们连成闭合回路，并悬挂在水平、光滑、不导电的圆棒两侧．在金属杆AB下方距离为h处有高度为H（H＞h）匀强磁场，磁感应强度大小为B，方向与回路平面垂直，此时，CD刚好处于磁场的下边界．现从静止开始释放金属杆AB，经过一段时间下落到磁场的上边界，加速度恰好为零，此后便进入磁场．求金属杆AB

（1）进入磁场前流过的电量；

（2）释放瞬间每根导线的拉力；

（3）穿过磁场区域的过程，回路中产生的焦耳热．

完型填空。
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