题目内容
(1)圆形匀强磁场区域的最小面积.
(2)粒子在磁场中运动的时间.
(3)b到O的距离.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241157417801057.gif)
(1)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115741811789.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115741998630.gif)
(1)带电粒子在磁场中运动时,洛仑兹力提供向心力
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241157420141638.gif)
(1) (2分)
带电粒子在磁场中做匀速圆周运动,连接粒子在磁场区入射点和出射点弦长为:
(2) (2分)
要使圆形匀强磁场区域面积最小,其半径刚好为:
(3) (2分)
其最小面积为:
(1分)
(2)带电粒子在磁场中运行的周期为:
T=2πR/v0="2πm/qB " (4) (2分)
轨迹圆弧对应的圆心角为1200,带电粒子在磁场中运动的时间为
(2分)
(3)由几何关系得ob的距离:
(5) (2分)
由(1)(5)式解得:d=3mv0/qB (1分)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241157420141638.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115742029568.gif)
带电粒子在磁场中做匀速圆周运动,连接粒子在磁场区入射点和出射点弦长为:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115742045618.gif)
要使圆形匀强磁场区域面积最小,其半径刚好为:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115742061408.gif)
|
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115741811789.gif)
(2)带电粒子在磁场中运行的周期为:
T=2πR/v0="2πm/qB " (4) (2分)
轨迹圆弧对应的圆心角为1200,带电粒子在磁场中运动的时间为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115741998630.gif)
(3)由几何关系得ob的距离:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115742107608.gif)
由(1)(5)式解得:d=3mv0/qB (1分)
![](http://thumb2018.1010pic.com/images/loading.gif)
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