题目内容
电路如图所示,电源电动势
,内阻
,电阻
,
,
,C为平行板电容器,其电容C=3.0pF,虚线到两极板距离相等,极板长
,两极板的间距
。
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250016441404089.jpg)
(1)若开关S处于断开状态,则当其闭合后,求流过R4的总电量为多少?
(2)若开关S断开时,有一带电微粒沿虚线方向以
的初速度射入C的电场中,刚好沿虚线匀速运动,问:当开关S闭合后,此带电微粒以相同初速度沿虚线方向射入C的电场中,能否从C的电场中射出?(要求写出计算和分析过程,g取
)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001644031553.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001644047452.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001644062518.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001644078608.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001644093529.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001644109524.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001644125600.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250016441404089.jpg)
(1)若开关S处于断开状态,则当其闭合后,求流过R4的总电量为多少?
(2)若开关S断开时,有一带电微粒沿虚线方向以
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001644156635.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001644171538.png)
(1)
;(2)不能从C的电场中射出.
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001644187635.png)
试题分析:(1)S断开时,电阻R3两端电压为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250016442031102.png)
S闭合后,外阻为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250016442181047.png)
路端电压为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001644234905.png)
电阻R3两端电压为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001644249996.png)
则所求流过R4的总电量为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250016442651096.png)
(2)设微粒质量为m,电量为q,当开关S断开时有
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001644281796.png)
当开关S闭合后,设微粒加速度为a,则
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001644296932.png)
假设微粒能从C的电场中射出,则水平方向
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001644312515.png)
竖直方向
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001644327648.png)
由以上各式得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001644343168.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001644359798.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001644374431.png)
故微粒不能从C的电场中射出。
![](http://thumb2018.1010pic.com/images/loading.gif)
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