题目内容
(20分)如图所示,直线MN上方存在着垂直纸面向里、磁感应强度为B的匀强磁场,质量为m、电荷量为-q(q>0)的粒子1以速度v1=v0从O点垂直射入磁场,其方向与MN的夹角
=30o;质量为m、电荷量为+q的粒子2以速度
也从O点垂直射入磁场,其方向与MN的夹角
=60o。已知粒子l、2同时到达磁场边界的A、B两点(图中未画出),不计粒子的重力及粒子间的相互作用。
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/2014082500402510020673.png)
(1)请画出粒子1和2在磁场中运动的轨迹;
(2)求两粒子在磁场边界上的穿出点A、B之间的距离d;
(3)求两粒子进入磁场的时间间隔
t;
(4)若MN下方有一匀强电场,使两粒子在电场中相遇,其中的粒子1做匀加速直线运动。求电场强度E的大小。
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004025037310.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004025053551.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004025069339.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/2014082500402510020673.png)
(1)请画出粒子1和2在磁场中运动的轨迹;
(2)求两粒子在磁场边界上的穿出点A、B之间的距离d;
(3)求两粒子进入磁场的时间间隔
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004025115319.png)
(4)若MN下方有一匀强电场,使两粒子在电场中相遇,其中的粒子1做匀加速直线运动。求电场强度E的大小。
试题分析:(1)如图所示(2分)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250040251314960.jpg)
(2)粒子在匀强磁场中做匀速圆周运动
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004025162761.png)
粒子1射出点A与O点的距离
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004025178831.png)
粒子2射出点B与O点的距离
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004025193839.png)
故
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004025209626.png)
代入数据得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004025225820.png)
(3)粒子做圆周运动的周期
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004025240639.png)
设粒子1在磁场中转过的圆心角为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004025256330.png)
则运动的时间
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004025271671.png)
设粒子2在磁场中转过的圆心角为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004025287358.png)
则运动的时间
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004025303710.png)
所以
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250040253181012.png)
(4)由题意得,电场强度的方向应与粒子1穿出磁场方向相反,则粒子1做们加速直线运动,粒子2做类平抛运动。
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250040253344377.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004025349585.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250040253651155.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004025396770.png)
解得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004025583649.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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