题目内容
如图所示真空中在直线DC与EF间宽为d的区域内有强度为B的匀强磁场方向如图,质量m带电+q的粒子以与DC成θ角的速度v0垂直射入磁场中。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241616418253575.jpg)
求(1)要使粒子只能从DC射出,则初速度v0应满足什么条件?
(2)从DC边飞出的粒子飞行的时间是多少?
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241616418253575.jpg)
求(1)要使粒子只能从DC射出,则初速度v0应满足什么条件?
(2)从DC边飞出的粒子飞行的时间是多少?
(1)
(2)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824161642044698.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241616419031103.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824161642044698.png)
试题分析:(1)带电粒子在磁场中从DC射出的临界状态的轨迹图如下图,临界半径R0,由
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824161642262749.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824161642387754.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241616425123440.png)
故粒子只能从DC飞出,必有轨迹半径
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824161642668444.png)
由
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824161642792781.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241616432141129.png)
有:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824161643338169.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241616419031103.png)
(2)运动时间由
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824161643853985.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241616441031080.png)
点评:本题画出轨迹的临界状态图示解题关键,由几何关系找出轨迹半径,由洛伦兹力等于向心力求出粒子速度,由圆心角求出运动时间。
![](http://thumb2018.1010pic.com/images/loading.gif)
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