题目内容
.如图所示,电源电动势为E,内阻为r,合上开关S后各电灯都能发光.如果某一时刻灯L1的灯丝烧断,之后各灯虽亮度变化,但并未损坏,则( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241320477515531.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241320477515531.png)
A.L3变亮,L2、L4变暗 | B.L2、L3变亮,L4变暗 |
C.L4变亮,L2、L3变暗 | D.L3、L4变亮,L2变暗 |
B
L1的灯丝烧断即该支路断路,即
并联电路的总电阻增大,所以电路的路端总电阻增大,故电路路端电压增大,即
两端的电压增大,通过
的电流增大,所以
变亮,因为电路的总电流减小,所以通过
支路的电流减小,故通过
的电流减小,所以
变暗,
两端的电压减小,又因为
支路两端电压增大,所以
两端电压升高,即通过
的电流相比于
烧断前的电流是变大了,故
变亮,所以B正确。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132047970441.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132048001350.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132048001350.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132048001350.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132048095435.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132048126326.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132048126326.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132048126326.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132048095435.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132048578341.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132048578341.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132048625313.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824132048656343.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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