题目内容
如图甲所示,理想变压器原线圈有100匝,其两端接图乙正弦式电压,副线圈有20匝,其两端接有三盏相同的灯泡L1、L2和L3,电阻均为2Ω,电键S闭合,交流电流表视为理想电表,导线电阻不计。下列说法正确的是
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082421092212112833.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082421092212112833.jpg)
A.副线圈的交变电流频率为0.05 Hz |
B.灯泡L2的电功率为0.25 W |
C.若将电键S断开,电流表的示数增大 |
D.若将电键S断开,灯泡L1的电功率增大 |
B
试题分析:变压器不改变交流电的频率,故副线圈交流电频率等于原线圈交流电频率为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824210922136585.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242109236181109.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824210924664341.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824210925459839.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824210924664341.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824210927144945.png)
若将电键S断开,副线圈中电阻增大,电压不变,所以电流减小,故原线圈中电流减小,C错误
通过灯泡
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824210927877263.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824210928657452.png)
故选B
点评:注意交流电有效值的转换,变压器不改变交流电频率,这一点需要注意
![](http://thumb2018.1010pic.com/images/loading.gif)
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