题目内容
真空中一平行板电容器,两极板分别由铂和钾(其极限波长分别为λ1和λ2)制成,板面积为S,间距为d.设影响电容器电容因素的表达式为εS/d (其中ε为常数),现用波长为λ(λ1<λ<λ2)的单色光持续照射两板内表面,则电容器的最终带电量为
A.dhc(λ–λ1)/eεSλλ1 | B.dhc(λ2–λ)/eεSλλ2 |
C.εShc (λ2–λ)/edλλ2 | D.εShc (λ–λ1)/edλλ1 |
C
试题分析:铂的极限波长为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824202214335349.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824202215333375.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824202216285535.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824202216925502.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242022175021394.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824202218063448.png)
光电子不断从钾极板发出,又不断到达铂极板,使电容器带电不断增加,电压也不断增大,这个电压是使光电子减速的反向电压.当某时刻,光电子恰好到达铂极板时其速度减为零,则电容器的电量达到最大值Q=CU(这里的电压U相当于反向截止电压.)
由动能定理可以得到:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242022191551059.png)
平行板电容器的电容:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824202220154685.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242022209181152.png)
故选C
点评:本题难度较大,将光电效应和电容器、带电粒子在电场中的运动联系起来.解决本题时可用排除法:根据
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824202216285535.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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