题目内容
如图5所示,静止的电子在加速电压U1的作用下从O经P板的小孔射出,又垂直进入平行金属板间的电场,在偏转电压U2的作用下偏转一段距离.现使U1加倍,要想使电子的运动轨迹不发生变化,应该 ( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241414511843055.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241414511843055.png)
A.使U2加倍 |
B.使U2变为原来的4倍 |
C.使U2变为原来的![]() |
D.使U2变为原来的1/2 |
A
要使电子的运动轨迹不变,则应使电子进入偏转电场后任一水平位移x所对应的偏转距离y保持不变.由y=
at2=
·
·(
)2=
和qU1=
mv02得y=
,可见在x、y一定时,U2∝U1.故A项正确.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141451278338.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141451278338.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141451371699.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141451512418.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141451590919.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141451278338.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141451699717.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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