题目内容
如图所示,两根平行放置的导电轨道,间距为L,倾角为θ,轨道间接有电动势为E(内阻不计)的电源.现有一根质量为m、电阻为R的金属杆ab垂直放于导电轨道上静止.轨道的摩擦和电阻均不计.要使ab杆静止,磁感应强度应为____________.![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241209416122417.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241209416122417.jpg)
mgRtanθ/EL
金属杆受力如图所示,导线中的电流
①
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241209416592535.jpg)
根据平衡条件:BIL="mgtanθ " ②
联立①和②得B=mgRtanθ/EL.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120941628290.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241209416592535.jpg)
根据平衡条件:BIL="mgtanθ " ②
联立①和②得B=mgRtanθ/EL.
![](http://thumb2018.1010pic.com/images/loading.gif)
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