题目内容
(10分)如图所示,abcd是一边长为l的匀质正方形导线框,总电阻为R,今使线框以恒定速度v水平向右穿过方向垂直于纸面向里的匀强磁场区域.已知磁感应强度为B,磁场宽度为3l,求线框在进入磁场区和穿出磁场区两个过程中a b两点间电势差的大小.
![](http://thumb.zyjl.cn/pic2/upload/papers/20140825/201408250033236181822.jpg)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140825/201408250033236181822.jpg)
导线框在进入磁场区过程中
,导线框在穿出磁场区过程中![](http://thumb.zyjl.cn/pic2/upload/papers/20140825/20140825003323649757.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140825/201408250033236816833.jpg)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140825/20140825003323634789.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140825/20140825003323649757.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140825/201408250033236816833.jpg)
试题分析:导线框在进入磁场区过程中,ab相当于电源,等效电路如图甲所示.外电路总电阻为
![](http://thumb.zyjl.cn/pic2/upload/papers/20140825/20140825003323696599.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140825/20140825003323712510.png)
则Uab两端电压为
![](http://thumb.zyjl.cn/pic2/upload/papers/20140825/20140825003323743995.png)
导线框全部进入过程中,磁通量不变,感应电流
![](http://thumb.zyjl.cn/pic2/upload/papers/20140825/20140825003323759344.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140825/20140825003323774745.png)
导线框在穿出磁场区过程中,cd相当于电源,等效电路如图乙所示.外电路总电阻为
![](http://thumb.zyjl.cn/pic2/upload/papers/20140825/20140825003323805620.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140825/20140825003323712510.png)
由法拉第电磁感应定律和闭合电路欧姆定律
![](http://thumb.zyjl.cn/pic2/upload/papers/20140825/20140825003323837555.png)
![](http://thumb.zyjl.cn/pic2/upload/papers/20140825/201408250033238521029.png)
则Uab两端电压为
![](http://thumb.zyjl.cn/pic2/upload/papers/20140825/20140825003323868966.png)
![](http://thumb.zyjl.cn/images/loading.gif)
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