题目内容
如图所示,虚线框内有匀强电场,AA′、BB′、CC′是该电场的三个等势面,相邻等势面间的距离为0.5cm,其中BB′为零势面。一个质量为m,电量为q的粒子沿AA′方向以初动能EK自图中的p点进入电场,刚好从C′点离开电场。已知PA′=2cm,粒子的重力忽略不计,下列说法正确的是( ).
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241513343722305.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241513343722305.jpg)
A.该粒子通过零势面时的动能是1.25EK |
B.该粒子在p点的电势能是0.5EK |
C.该粒子达到C′点时的动能是1.5EK |
D.该粒子达到C′点时的电势能是0.5EK |
B
试题分析:根据等势面的分布情况和粒子的轨迹分析可知:粒子做类平抛运动,水平方向做匀速直线运动,竖直方向做匀加速直线运动.粒子从A到C,水平位移为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151334404491.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151334528476.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151334638492.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151334700628.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151334747350.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151334809344.png)
AC、粒子做类平抛运动,水平方向做匀速直线运动,有
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151334638492.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151334700628.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151335028484.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151335106455.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151334809344.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151335293817.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151334809344.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241513355111097.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151335605447.png)
B、BB'为零势能面,由上可知,粒子经过等势面BB'时总能量为是
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151335605447.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151335964665.png)
D、根据能量守恒得,该粒子到达
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151334809344.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151336291904.png)
故选B
点评:本题首先要分析出粒子做类平抛运动,关键是研究粒子经过BB'面时总能量,根据能量守恒研究经过其他等势面时的电势能
![](http://thumb2018.1010pic.com/images/loading.gif)
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