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,接在一个理想变压器两端,变压器起到降压作用。开关闭合前后,AB两端电功率相等,以下说法正确的是
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250043152654522.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004315249940.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250043152654522.png)
A.流过r的电流方向每秒钟变化50次 | B.变压器原线圈匝数大于副线圈匝数 |
C.开关从断开到闭合时,电流表示数变小 | D.![]() |
BD
试题分析:由
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004315249940.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004315327636.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004315343631.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004315359629.png)
闭合后,副线圈中的总电流为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004315374767.png)
由题意
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004315390735.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004315281516.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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