题目内容
如图所示的狭长区域内有垂直于纸面向里的匀强磁场,区域的左、右两边界均沿竖直方向,磁场磁感应强度的大小为B.某种质量为m,电荷量q的带正电粒子从左边界上的P点以水平向右的初速度v进入磁场区域,该粒子的运动轨迹恰好与磁场右边界相切。重力的影响忽略不计。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241635251524939.jpg)
(1)求该粒子在磁场中做圆周运动的轨道半径和周期;
(2)求磁场左、右两边界之间的距离L;
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241635251524939.jpg)
(1)求该粒子在磁场中做圆周运动的轨道半径和周期;
(2)求磁场左、右两边界之间的距离L;
(1)
,
(2)L![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824163525620608.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824163525261692.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824163525448775.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824163525620608.png)
试题分析:(1)过程中洛伦兹力充当向心力,所以可得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824163525963789.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824163526119697.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824163526306661.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824163526525769.png)
(2)该粒子的运动轨迹恰好与磁场右边界相切,故
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824163526837780.png)
点评:做此类型问题,需要画轨迹,定圆心,求半径
![](http://thumb2018.1010pic.com/images/loading.gif)
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