题目内容
如图所示,一正弦交流电瞬时值为
,通过一个理想电流表,接在一个理想的降压变压器两端。以下说法正确的是
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250048121963071.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004812165952.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250048121963071.jpg)
A.流过r的电流方向每秒钟变化50次 |
B.变压器原线圈匝数小于副线圈匝数 |
C.开关从断开到闭合时,电流表示数变小 |
D.开关闭合前后,AB两端电功率可能相等 |
D
试题分析:由交变电流表达式可知些交流电的周期为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004812211821.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250048122271016.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250048122581315.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004812274932.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004812289516.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004812305436.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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