题目内容
如图所示,在空间有一坐标系xoy,直线OP与x轴正方向的夹角为
,第一象限内有两个方向都垂直纸面向外的匀强磁场区域Ⅰ和Ⅱ,直线OP是他们的边界,OP上方区域Ⅰ中磁场的磁感应强度为B。一质量为m,电荷量为q的质子(不计重力)以速度v从O点沿与OP成
角的方向垂直磁场进入区域Ⅰ,质子先后通过磁场区域Ⅰ和Ⅱ后,恰好垂直打在x轴上的Q点(图中未画出),则: ( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241336013836037.png)
A.粒子在第一象限中运动的时间为![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133601414774.png)
B.粒子在第一象限中运动的时间为![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133601554725.png)
C.Q点的横坐标为![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133601585931.png)
D.Q点的横坐标为![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133601632948.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133601289546.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133601289546.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241336013836037.png)
A.粒子在第一象限中运动的时间为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133601414774.png)
B.粒子在第一象限中运动的时间为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133601554725.png)
C.Q点的横坐标为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133601585931.png)
D.Q点的横坐标为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133601632948.png)
AC
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082413360167911432.png)
由
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241336017101213.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133601757705.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241336017881129.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133601866679.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133601414774.png)
A对,B错;OQ=Rcos30+r,由图知r=R/2,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133601757705.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824133601585931.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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