题目内容
(14分)如图所示,用一台变压器给100盏220V,60W的电灯供电,变压器的初级线圈匝数与次级线圈的匝数之比是3。初级线圈的输入电压是660V,次级线圈的电阻为0.2Ω。求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250001366554602.png)
(l)空载时次级线圈的端电压和输出功率;
(2)接通时次级线圈的端电压;
(3)每盏灯的实际功率.
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250001366554602.png)
(l)空载时次级线圈的端电压和输出功率;
(2)接通时次级线圈的端电压;
(3)每盏灯的实际功率.
(1)220V 0 (2)214.68V (3)57.1W
试题分析:(1)将变压器视为理想变压器。设空载时次级线圈的端电压为U2。
由
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000136671691.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000136687680.png)
因为空载,次级线圈的负载电阻R2→∞,次级线圈中的电流为零I2=0,P=I2U2=0
(2)接通电路后,100盏灯并联的总电阻为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250001367021543.png)
次级线圈中的电流
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000136718918.png)
次级线圈的端电压U′2=I2R外=214.68(V)
(3)每盏灯的实际功率
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250001367331703.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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