题目内容
一个质量
、长
、宽
、电阻
的矩形线圈,从
高处由静止开始自由下落,进入一个匀强磁场,如图12-4-15所示.线圈下边刚进入磁场时,由于磁场力作用,线圈正好作匀速运动,求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241139471723807.jpg)
(1)磁场的磁感应强度B
(2)如果线圈下边通过磁场所经历的时间
,求磁场区域的高度![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113947203218.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113946579559.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113946595396.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113946610415.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113946626302.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113946642404.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241139471723807.jpg)
(1)磁场的磁感应强度B
(2)如果线圈下边通过磁场所经历的时间
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113947188410.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113947203218.gif)
0.4T 1.55m
(1)线框进入磁场时的速度
,刚进入磁场时线圈正好作匀速运动,
所以进入磁场时受力平衡
则 ![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113947250730.gif)
(2)由于线圈进入磁场时是匀速运动,线圈全部进入磁场的时间![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113947281712.gif)
由于整个线圈全部进入磁场后,闭合回路中没有磁通量的变化,所以没有感应电流,此时线圈不受安培力,故线圈只受重力的作用.线圈全部进入磁场后的运动情况是:以
的初速度做匀加速运动,加速度是
,而加速运动的时间![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113947344557.gif)
线圈全部进入磁场时到刚好将要开始离开磁场时线圈移动的位移![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113947359635.gif)
代人解得:H=1.05m 故![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113947375789.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113947219603.gif)
所以进入磁场时受力平衡
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113947234707.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113947250730.gif)
(2)由于线圈进入磁场时是匀速运动,线圈全部进入磁场的时间
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113947281712.gif)
由于整个线圈全部进入磁场后,闭合回路中没有磁通量的变化,所以没有感应电流,此时线圈不受安培力,故线圈只受重力的作用.线圈全部进入磁场后的运动情况是:以
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113947312423.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113947328512.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113947344557.gif)
线圈全部进入磁场时到刚好将要开始离开磁场时线圈移动的位移
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113947359635.gif)
代人解得:H=1.05m 故
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113947375789.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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