题目内容
(10分)一个质量为m电荷量为q的带电粒子从x轴上的P(a,0)点以速度v,沿与x正方向成60°的方向射入第一象限内的匀强磁场中,并恰好垂直于y轴射出第一象限。求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241224126241363.gif)
(1)匀强磁场的磁感应强度B和射出点的坐标。
(2)带电粒子在磁场中的运动时间是多少?
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241224126241363.gif)
(1)匀强磁场的磁感应强度B和射出点的坐标。
(2)带电粒子在磁场中的运动时间是多少?
(1)(0,
)
(2)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824122412655549.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824122412639267.gif)
(2)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824122412655549.gif)
(1)设磁感应强度为B,粒子在磁场中做匀速圆周运动的半径为r.
由
(1分)
得
(1分)
粒子在磁场中运动情况如图
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241224127174612.jpg)
由几何知识有
(1分)
有上两式得
(1分)
又由几何知识知
(1分)
出射点到O点的距离为
(1分)
所以出射点的坐标为:(0,
)(1分)
(2)设粒子在磁场中做匀速圆周运动的周期为T,则
(1分)
由图知,粒子在磁场中做圆周运动对应的圆心角为
=180o-60o=1200 (1分)
所以,粒子在磁场中运动的时间是
(1分)
由
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824122412671530.gif)
得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824122412686494.gif)
粒子在磁场中运动情况如图
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241224127174612.jpg)
由几何知识有
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824122412733604.gif)
有上两式得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824122412780586.gif)
又由几何知识知
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824122412795680.gif)
出射点到O点的距离为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824122412811544.gif)
所以出射点的坐标为:(0,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824122412639267.gif)
(2)设粒子在磁场中做匀速圆周运动的周期为T,则
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824122412842891.gif)
由图知,粒子在磁场中做圆周运动对应的圆心角为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824122412889200.gif)
所以,粒子在磁场中运动的时间是
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241224129201065.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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