题目内容
如图所示,有一垂直于纸向外的有界匀强磁场,磁场的磁感应强度为B,其边界为一边长L的正三角形(边界上有磁场)ABC为三角形的三个顶点.今有一质量为m、电荷量为+q的粒子(不计重力),以速度
,从AB边上的某点P既垂直于AB边又垂直于磁场的方向射入,然后从BC边上某点Q射出.若从P点射入的该粒子能从Q点射出,则
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250048192942127.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004819372695.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004819278828.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250048192942127.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004819325878.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004819341784.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004819356736.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004819372695.png)
AD
试题分析:由半径公式可得粒子在磁场中做圆周运动的半径为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250048194031052.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250048194191152.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250048194508310.png)
当圆心处于O2位置时,粒子从P2射入,打在BC边的Q点,由于此时Q点距离AB最远为圆的半径
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004819465549.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250048194811279.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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