题目内容
如图,理想变压器原、副线圈匝数 n1: n2 : n3 =" 3" : 2 : 1 ,副线圈 n2接有 “8V 8 W ” 的灯泡 Ll、L2,副线圈n3上接有 “6 V 9W ”的灯L3、L4.原线圈上接有电阻 R1 = 3
,当 a 、 b端接入交变电源后, Ll、L2 正常发光,则交变电源的输出功率为( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241150504234802.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115050407335.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241150504234802.png)
A.72W | B.36 W | C.34W | D.24 W |
B
由题意可知n2的输出电压为8V;因电压之比等于匝数之比,故输入电压为
×8=12V;
则n3输出电压U3=
×12=4V;
由功率P=
可知,灯泡L3、L4的电阻为
=4Ω,且都正常发光,
则n3输出的功率2P实=2
=2×
=8W;
则可知变压器的总功率P总=2×8+8=24W;
由P=UI可得:输入端电流为I=
=2A;
则R1消耗的功率P1=I2R1=12W;
则交变电流输出的功率为12+24W=36W;
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115050454278.png)
则n3输出电压U3=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115050470263.png)
由功率P=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115050548336.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115050563327.png)
则n3输出的功率2P实=2
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115050594358.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115050610342.png)
则可知变压器的总功率P总=2×8+8=24W;
由P=UI可得:输入端电流为I=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115050672369.png)
则R1消耗的功率P1=I2R1=12W;
则交变电流输出的功率为12+24W=36W;
![](http://thumb2018.1010pic.com/images/loading.gif)
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