题目内容
如图17甲所示,静止在匀强磁场中的
Li核俘获一个速度为v0=7.7×104 m/s的中子而发生核反应:
Li+
n→
H+
He,若已知
He的速度v2=2.0×104 m/s,其方向与反应前中子速度方向相同,试求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241358043438988.jpg)
(1)
H的速度大小和方向;
(2)在图乙中,已画出并标明两粒子的运动轨迹,请计算出轨道半径之比;
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824135803781302.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824135803781302.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824135804000268.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824135804078272.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824135804125292.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824135804125292.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241358043438988.jpg)
(1)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824135804078272.png)
(2)在图乙中,已画出并标明两粒子的运动轨迹,请计算出轨道半径之比;
(1) -1.0×103 m/s,方向与v0相反(2) 3∶40
(1)反应前后动量守恒:m0v0=m1v1+m2v2(v1为氚核速度,m0、m1、m2分别代表中子、氚核、氦气质量)
代入数值可解得:v1=-1.0×103 m/s,方向与v0相反.
(2)
H和
He在磁场中均受洛伦兹力f,
做匀速圆周运动的半径之比r1∶r2=
∶
=3∶40.
本题考查核反应前后的带电粒子在磁场中的偏转和动量守恒定律,反应前后动量守恒,列式求解,由带电粒子在磁场中洛伦兹力提供向心力,推导出半径公式求解
代入数值可解得:v1=-1.0×103 m/s,方向与v0相反.
(2)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824135804078272.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824135804125292.png)
做匀速圆周运动的半径之比r1∶r2=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824135804842649.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824135805061679.png)
本题考查核反应前后的带电粒子在磁场中的偏转和动量守恒定律,反应前后动量守恒,列式求解,由带电粒子在磁场中洛伦兹力提供向心力,推导出半径公式求解
![](http://thumb2018.1010pic.com/images/loading.gif)
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