题目内容
(10分)如图所示,质量为m的单匝正方形线圈,其边长为L,在距底边2L的匀强磁场
上方由静止开始自由下落,设线圈下落过程中线框平面始终位于纸面内且底边保持水平,当线框的底边刚进入磁场区域时,恰能在匀强磁场中做匀速运动。若磁场的磁感应强度为B,求:(1)线圈的电阻多大?
(2)线圈进入磁场的过程中单
位时间内有多少机械能转化为电能?![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241245271623387.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082412452714685.gif)
(2)线圈进入磁场的过程中单
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082412452714665.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241245271623387.jpg)
(10分)(1)
,mg=BIL,
…………3分
上式联立得:
,………………2分
(2)P=mgv,所以
…………
5分
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124527177330.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124527489364.gif)
上式联立得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124527817673.gif)
(2)P=mgv,所以
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824124527832527.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082412452784872.gif)
略
![](http://thumb2018.1010pic.com/images/loading.gif)
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