题目内容
(19分)如图所示,在铅板A上放一个放射源C可向各个方向射出速率为
的
射线,B为金属网,A、B连接在电路上,电源电动势为
,内阻为
,滑动变阻器总阻值为
,图中滑动变阻器滑片置于中点,A、B间距为d,M为荧光屏(足够大),它紧挨者金属网外侧,已知
粒子的质量为
,不计
射线所形成的电流对电路的影响,求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250015012891833.png)
(1)闭合开关S后,AB间的场强的大小是多少?
(2)
粒子到达金属网B的最长时间?
(3)切断开关S,并撤去金属网B,加上垂直纸面向内、范围足够大的匀强磁场,磁感应强度大小为B,设加上B后
粒子仍能到达荧光屏。这时在竖直方向上能观察到荧光屏亮区的长度是多少?
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001501102265.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001501133339.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001501149318.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001501164260.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001501242303.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001501133339.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001501258337.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001501133339.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250015012891833.png)
(1)闭合开关S后,AB间的场强的大小是多少?
(2)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001501133339.png)
(3)切断开关S,并撤去金属网B,加上垂直纸面向内、范围足够大的匀强磁场,磁感应强度大小为B,设加上B后
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001501133339.png)
(1)
(2)
(3)![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250015013831096.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001501336998.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250015013521124.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250015013831096.png)
试题分析: (1)由闭合电路欧姆定律得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001501398616.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250015013981081.png)
则电场强度:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250015014141204.png)
(2)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001501133339.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250015014611269.png)
分析可知,沿A板方向射出的
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001501133339.png)
根据运动学公式:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001501492668.png)
则
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250015015231373.png)
(3)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001501133339.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001501554754.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001501570671.png)
荧光亮斑区的上边界就是沿A板射出的
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001501133339.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250015016175735.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001501726808.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250015017421462.png)
荧光亮斑区的下边界就是
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001501133339.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001501773789.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250015017881092.png)
在竖直方向上亮斑区的长度为:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250015018041362.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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