题目内容
(2011·淄博模拟) (12分)如图所示,理想变压器B的原线圈跟副线圈的匝数比n1∶n2=2∶1,交流电源电压U=311sin100πt V,F为熔断电流为I0="1.0" A的保险丝,负载为一可变电阻.
(1)当电阻R="100" Ω时,保险丝能否被熔断?
(2)要使保险丝不被熔断,电阻R的阻值应不小于多少?变压器输出的电功率不能超过多少?![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241409370155420.png)
(1)当电阻R="100" Ω时,保险丝能否被熔断?
(2)要使保险丝不被熔断,电阻R的阻值应不小于多少?变压器输出的电功率不能超过多少?
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241409370155420.png)
(1)保险丝不会熔断 (2)电阻R的阻值不能小于55 Ω
电功率不能大于220 W
电功率不能大于220 W
原线圈电压的有效值为U1=
V="220" V
由
=
得副线圈两端的电压
U2=
U1=
×220 V="110" V
(1)当R="100" Ω时,副线圈中电流
I2=
=
A="1.10" A. (3分)
由U1I1="U2I2" 得原线圈中的电流为
I1=
I2=
×1.10 A="0.55" A,由于I1<I0 (熔断电流),故保险丝不会熔断. (2分)
(2)设电阻R取某一值R0时,原线圈中的电流I1刚好到达熔断电流I0,即I1="1.0" A,则副线圈中的电流为
I2=
I1=
·I1=2×1.0 A="2.0" A
变阻器阻值为:R0=
=
Ω=55Ω (3分)
此时变压器的输出功率为
P2=I2·U2=2.0×110 W="220" W (2分)
可见,要使保险丝F不被熔断,电阻R的阻值不能小于55 Ω,
输出的电功率不能大于220 W. (2分)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140937109268.png)
由
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140937187280.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140937265220.png)
U2=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140937343225.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140937390165.png)
(1)当R="100" Ω时,副线圈中电流
I2=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140937468250.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140937561179.png)
由U1I1="U2I2" 得原线圈中的电流为
I1=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140937655253.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140937749217.png)
(2)设电阻R取某一值R0时,原线圈中的电流I1刚好到达熔断电流I0,即I1="1.0" A,则副线圈中的电流为
I2=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140937842255.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140937920235.png)
变阻器阻值为:R0=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140937967262.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140938061242.png)
此时变压器的输出功率为
P2=I2·U2=2.0×110 W="220" W (2分)
可见,要使保险丝F不被熔断,电阻R的阻值不能小于55 Ω,
输出的电功率不能大于220 W. (2分)
![](http://thumb2018.1010pic.com/images/loading.gif)
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