题目内容
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082411541542312939.jpg)
(2)电子打到荧光屏上的位置P偏离荧光屏中心O的距离OP;
(3)若撤去M、N间的电压U2,而在两平行板中的圆形区域内(如图b所示)加一磁感应强度为B=0.001T的匀强磁场,圆形区域的中心正好就是两平行板空间部分的中心,要使电子通过磁场后仍打在荧光屏上的P点处,圆形区域的半径r为多少?(结果中可含有反三角函数)
(1)
(2)7cm(3)1.14cm
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115415438526.gif)
(1)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115415454535.gif)
∴
(6分)
(2)
(6分)
(3)∵
∴
(2分)
(6分)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115415454535.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241154154691085.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115415438526.gif)
(2)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241154155011020.gif)
(3)∵
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115415516600.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115415547850.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241154155471015.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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