题目内容
(10分)如图所示,虚线所围圆形区域内有方向垂直纸面向里的匀强磁场,磁感应强度为B.一束电子沿圆形区域的直径方向以速度v射入磁场,电子束经过磁场区后,其运动的方向与原入射方向成
角.设电子质量为m,电荷量为e,不计电子之间的相互作用力及所受的重力.求:
(1)电子在磁场中运动的时间t
(2)圆形磁场区域的半径r.![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241517170002801.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151716907291.png)
(1)电子在磁场中运动的时间t
(2)圆形磁场区域的半径r.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241517170002801.png)
(1)
(2)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151717250942.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151717125654.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151717250942.png)
试题分析:1)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151717422674.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151717609742.png)
解得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151717125654.png)
(2)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151717890754.png)
由几何关系得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151718061744.png)
解得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151717250942.png)
点评:需要注意的是粒子在磁场中的运动和速度无关,只和轨迹所对的圆心角有关
![](http://thumb2018.1010pic.com/images/loading.gif)
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