题目内容
示波器可以视为加速电场与偏转电场的组合,若已知前者的电压为U1,后者电压为U2,极板长为L,板间距为d,且电子加速前初速可忽略.则示波器的灵敏度(偏转电场中每单位偏转电压所引起的偏转量h/U称为“灵敏度”)与加速电场、偏转电场的关系正确的是( ).
A.L越大,灵敏度越大 | B.d越大,灵敏度越大 |
C.U1越大,灵敏度越小 | D.灵敏度与U1_无关 |
A C
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=
,
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/20140824/20140824125442320338.png)
(
)2=
=
,
所以示波管的灵敏度
=
,
所以要提高示波管的灵敏度可以增大l,减小d和减小U1,所以AC正确.
故选AC.
eU1=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125442320338.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/20140824/20140824125442351603.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/20140824/20140824125442320338.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125442320338.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125442429515.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125442460384.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125442491831.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125442523590.png)
所以示波管的灵敏度
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125442538417.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125442554547.png)
所以要提高示波管的灵敏度可以增大l,减小d和减小U1,所以AC正确.
故选AC.
![](http://thumb2018.1010pic.com/images/loading.gif)
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