题目内容
(12分)如图所示,在虚线所示宽度范围内,用场强为
的匀强电场可使初速度是
的某种正离子偏转
角.在同样宽度范围内,若改用方向垂直纸面向外的匀强磁场,使该离子穿过该区域,并使偏转角也为
,(不计离子的重力)求:
(1)匀强磁场的磁感应强度是多大?
(2)离子穿过电场和磁场的时间之比是多大?
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241312474114618.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131247208318.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131247239323.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131247255297.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131247255297.png)
(1)匀强磁场的磁感应强度是多大?
(2)离子穿过电场和磁场的时间之比是多大?
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241312474114618.jpg)
解:(1)设粒子的质量
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131247427337.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131247458310.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131247489280.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131247520512.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131247536653.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131247567741.png)
由①②③得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131247598935.png)
粒子在磁场中做匀速圆周运动
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131247614780.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131247629624.png)
由⑤⑥解得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131247661910.png)
由④⑦式解得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131247770771.png)
(2)粒子在电场中运动时间
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131247879563.png)
在磁场中运动时间
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131247910726.png)
而
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131248019954.png)
由⑧⑨⑩解出:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131248051688.png)
略
![](http://thumb2018.1010pic.com/images/loading.gif)
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