题目内容
如图所示,边长为a的正方形,内部充满垂直纸面向里的匀强磁场,磁感应强度为B,一束电子(质量为m,电量为e)以不同的速度水平射入磁场后,分别从A处和C处射出(不计电子重力)。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115713762773.gif)
求:(1)从A处射出的电子速度为多大
(2)从C处射出的电子经历的时间t
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115713762773.gif)
求:(1)从A处射出的电子速度为多大
(2)从C处射出的电子经历的时间t
(1)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115713778453.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115713793440.gif)
(1)电子从A处射出如图所示,则半径r=![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115713793233.gif)
由洛伦兹力提供向心力得:evB=m![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115713809241.gif)
联立解得 v=![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115713778453.gif)
(2)电子由C射出如图所示,易知圆弧占圆周的![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115713840221.gif)
又电子在磁场中的周期为 T=![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115713856558.gif)
则电子在磁场中的时间为t=
T=![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115713793440.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241157139032566.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115713793233.gif)
由洛伦兹力提供向心力得:evB=m
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115713809241.gif)
联立解得 v=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115713778453.gif)
(2)电子由C射出如图所示,易知圆弧占圆周的
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115713840221.gif)
又电子在磁场中的周期为 T=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115713856558.gif)
则电子在磁场中的时间为t=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115713840221.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115713793440.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241157139032566.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
练习册系列答案
相关题目