题目内容
(1)带电微粒在磁场中运动的速率;
(2)带电微粒在第一次到达y轴上时与O点的距离;
(3)微粒经过磁场打在x轴正方向上的某一点P,P到坐标原点O的距离也为12cm,求磁场的磁感应强度B。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082411532851310393.jpg)
(1)2.5×106m/s (2)12cm (3)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241153285131178.jpg)
(1)
(2分)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241153285457263.jpg)
(2分)
(2分)
射出电场后做匀速直线运动,则在磁场中的速度为2.5×106m/s (2分)
(2)与速度x轴的夹角![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115328591577.gif)
经过电场的偏距
(2分)
故有
(2分)
(3)作出粒子在磁场中的运动轨迹,如图
则
(3分)
因为![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115328654809.gif)
解得
(2分)
根据
(3分)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241153285291021.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241153285457263.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241153285601406.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115328576701.gif)
射出电场后做匀速直线运动,则在磁场中的速度为2.5×106m/s (2分)
(2)与速度x轴的夹角
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115328591577.gif)
经过电场的偏距
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241153286071392.gif)
故有
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241153286231223.gif)
(3)作出粒子在磁场中的运动轨迹,如图
则
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115328638561.gif)
因为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115328654809.gif)
解得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115328654874.gif)
根据
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241153286691300.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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