题目内容
如图所示,在真空室中有一水平放置的不带电平行板电容器,板间距离为d,电容为C,上板B接地。现有大量质量均为m、带电量均为q的小油滴,以相同的初速度持续不断地从两板正中间沿图中虚线所示方向射入,第一滴油滴正好落到下板A的正中央P点。如果能落到A板的油滴仅有N滴,且第N+1滴油滴刚好能飞离电场,假定落到A板的油滴的电量能被板全部吸收,不考虑油滴间的相互作用,重力加速度为g,则下列说法正确的是( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241316471521692.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241316471521692.png)
A.落到A板的油滴数![]() |
B.落到A板的油滴数![]() |
C.第N+1滴油滴通过电场的整个过程所增加的动能等于![]() |
D.第N+1滴油滴通过电场的整个过程所减少的机械能等于![]() |
A
没有电荷时:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131647480545.png)
落到A板N滴油滴时:
联立解得:
,A对。
第N+1滴油滴通过电场的整个过程,根据动能定理:![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241316475731150.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241316476201252.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241316476511414.png)
,C错;
减少的机械能等于克服电场力做的功。
,D错。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131647464720.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131647480545.png)
落到A板N滴油滴时:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131647511502.png)
联立解得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131647308560.png)
第N+1滴油滴通过电场的整个过程,根据动能定理:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241316475731150.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241316476201252.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241316476511414.png)
,C错;
减少的机械能等于克服电场力做的功。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824131647698911.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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