题目内容
如图所示,质量为M的导体棒ab,垂直放在相距为l的平行光滑金属轨道上。导轨平面与水平面的夹角为θ,并处于磁感应强度大小为B、方向垂直与导轨平面向上的匀强磁场中,左侧是水平放置、间距为d的平行金属板,R和Rx分别表示定值电阻和滑动变阻器的阻值,不计其他电阻。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242118213368604.png)
(1)调节Rx=R,释放导体棒,当棒沿导轨匀速下滑时,求通过棒的电流I及棒的速率v。
(2)改变Rx,待棒沿导轨再次匀速下滑后,将由放射源产生的α射线水平射入金属板间,若它能匀速通过,求此时的Rx。(已知质子质量为mP,设质子质量与中子质量相等,质子带电量为e)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242118213368604.png)
(1)调节Rx=R,释放导体棒,当棒沿导轨匀速下滑时,求通过棒的电流I及棒的速率v。
(2)改变Rx,待棒沿导轨再次匀速下滑后,将由放射源产生的α射线水平射入金属板间,若它能匀速通过,求此时的Rx。(已知质子质量为mP,设质子质量与中子质量相等,质子带电量为e)
(1)
,
(2)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242118235981234.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824211822085338.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824211822880388.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242118235981234.png)
试题分析:(1)当Rx=R棒沿导轨匀速下滑时,由平衡条件
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824211824222299.png)
安培力
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824211824939246.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824211822085338.png)
感应电动势
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824211826624251.png)
电流
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824211827404280.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824211822880388.png)
(2)微粒水平射入金属板间,能匀速通过,由平衡条件
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824211828512305.png)
棒沿导轨匀速,由平衡条件
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824211829573322.png)
金属板间电压
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824211830337261.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824211831632383.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242118235981234.png)
点评:本题考查了电磁感应现象中有关感应电流的计算,通过平衡条件求出金属棒的速度。
![](http://thumb2018.1010pic.com/images/loading.gif)
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