题目内容
如图所示的匀强电场中,有a、b、c三点,ab=5cm,bc=12cm,其中ab沿电场方向,bc和电场方向成60°角,一电子(其电荷量为e=1.6×10-19C)从a移到b电场力做功为Wab=3.2×10-18J求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241519088062527.jpg)
(1)匀强电场的场强大小及方向;
(2)电子从b移到c,电场力对它做功;
(3)a、c两点的电势差Uac等于多少?
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241519088062527.jpg)
(1)匀强电场的场强大小及方向;
(2)电子从b移到c,电场力对它做功;
(3)a、c两点的电势差Uac等于多少?
(1)400V/m b指向a(向左或水平向左都正确)(2)3.84×10—18J (3)—44V
试题分析:(1)电子从a移到b电场力做正功,可知电场力方向向右,则电场强度方向水平向左.电子从a移到b电场力做功为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151908868773.png)
电场强度E=400N/C
(2)从b到c,电场力做功是
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241519089621119.png)
(3)电子从a移到c,电场力做功
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241519091331121.png)
电子电势能减小
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151909211649.png)
设
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151909570465.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151909679663.png)
a、c两点的电势差
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151909742890.png)
点评:注意在涉及电势能的公式物理量一般代入符号运算,涉及电场力的公式一般不代入符号运算.
![](http://thumb2018.1010pic.com/images/loading.gif)
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