题目内容
如图17-4-7所示,理想变压器原副线圈的匝数比为1∶2,电源电压为220 V,A是额定电流为I0=1 A的保险丝,R为可调电阻,为不使原线圈中电流超过I1,R的阻值最低不小于多少欧?
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241216402541922.gif)
图17-4-7
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241216402541922.gif)
图17-4-7
880 Ω
由于保险丝的额定电流为I0=1 A,所以原线圈中允许输入的最大电流I1=I0=1 A(有效值),则变压器的最大输入功率为
P1=U1I1=220×1 W=220 W
由![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082412164027073.gif)
,得电阻R两端电压为
U2=
×220 V=440 V![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082412164027073.gif)
由于P入=P出,则变压器最大输出功率
P2=P1=220 W
由P2=
,知P2最大时,R最小,则R的最小值为
R=
Ω=880 Ω
P1=U1I1=220×1 W=220 W
由
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082412164027073.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241216402851302.jpg)
U2=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121640395506.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082412164027073.gif)
由于P入=P出,则变压器最大输出功率
P2=P1=220 W
由P2=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121640426297.gif)
R=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121640535631.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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