题目内容
如图所示为示波管的示意图,要使屏上的光点P向下偏移的距离增大,可以( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082412353590522207.png)
A.增大加速电压U1 | B.减小加速电压U1 |
C.增大偏转电压U2 | D.减小偏转电压U2 |
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082412353590522207.png)
BC
根据偏转方向做匀加速运动,分析电子的偏转位移的关系式,根据关系式来分析偏转位移与哪些物理量有关.
解:电子在加速电场中加速,根据动能定理可得,
eU1=
mv02
所以电子进入偏转电场时速度的大小为,
v0=![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123536123603.png)
电子进入偏转电场后的偏转的位移为,
h=
at2=![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123536108338.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241235361861069.png)
所以要使屏上的光点P向下偏移的距离增大,可以增大U2或减小U1,
故选BC
解:电子在加速电场中加速,根据动能定理可得,
eU1=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123536108338.png)
所以电子进入偏转电场时速度的大小为,
v0=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123536123603.png)
电子进入偏转电场后的偏转的位移为,
h=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123536108338.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824123536108338.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241235361861069.png)
所以要使屏上的光点P向下偏移的距离增大,可以增大U2或减小U1,
故选BC
![](http://thumb2018.1010pic.com/images/loading.gif)
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