题目内容
如图10所示,在坐标系xoy平面的x>0区域内,有电场强度E=2×105N/C,方向沿y轴负向的匀强电场和磁感应强度B=0.20 T,方向与xoy平面垂直向里的匀强磁场。在y轴上有一足够长的荧光屏MN,在x轴上的P(10,0)点处有一粒子发射枪连续不断的发射大量质量m=6.4×10-27kg,电量q=3.2×10-19C的带正电粒子,其向x轴方向发射的粒子恰能沿x轴做匀速直线运动。若撤去电场,并使粒子发射枪以P为轴在xoy平面内以角速度ω=2πrad/s逆时针转动(整个装置都处在真空中),求:
(1)带电粒子在磁场中运动的轨迹半径;
(2)荧光屏上闪光点的范围;
(3)荧光屏上闪光点从最高点移动到最低点所用的时间。![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241214270617895.jpg)
(1)带电粒子在磁场中运动的轨迹半径;
(2)荧光屏上闪光点的范围;
(3)荧光屏上闪光点从最高点移动到最低点所用的时间。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241214270617895.jpg)
(1)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121427077319.gif)
(2)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121427202516.gif)
(3)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121427217321.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121427077319.gif)
(2)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121427202516.gif)
(3)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121427217321.gif)
(1)由粒子在复合场中做匀速运动,有:
(1’)
撤去电场后,有
(1’)
∴ 粒子在磁场中运动的轨迹半径
(1’)
(2)画出右图可知,粒子最上端打在A点,最下端打在B点 (2’)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241214272809281.jpg)
(1’)
(1’)
∴![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121427326725.gif)
(3)粒子在磁场中做圆周运动的周期
(1’)
∴粒子在磁场中运动的时间可以忽略不计 (1’)
闪光点从最高点移到最低点的过程中,粒子枪转过的圆心角为
(1’)
∴ 用时
(1’)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121427233447.gif)
撤去电场后,有
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121427248540.gif)
∴ 粒子在磁场中运动的轨迹半径
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241214272641241.gif)
(2)画出右图可知,粒子最上端打在A点,最下端打在B点 (2’)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241214272809281.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121427295655.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121427311298.gif)
∴
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121427326725.gif)
(3)粒子在磁场中做圆周运动的周期
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241214273421556.gif)
∴粒子在磁场中运动的时间可以忽略不计 (1’)
闪光点从最高点移到最低点的过程中,粒子枪转过的圆心角为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121427358447.gif)
∴ 用时
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121427373755.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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