题目内容
(10分)有一台内阻为1Ω的发电机,供给一学校照明用电,如图所示。升压变压器原、副线圈匝数比为1:4,降压变压器原、副线圈匝数比为4:1,输电线的总电阻为4Ω。全校共有22个班,每班有“220V,40W”灯6盏,若保证全部电灯正常发光,则
(1)发电机的输出功率多大?
(2)发电机的电动势多大?
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241538234587156.jpg)
(1)发电机的输出功率多大?
(2)发电机的电动势多大?
(1) 5424W (2) 250 V (3) 97%.
试题分析:⑴由题意知 U4="220" V
则
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241538235511322.png)
由由降压变压器变压关系:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153823692725.png)
得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241538238481018.png)
由降压变压器变流关系:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153823988601.png)
得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153824082855.png)
又因为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241538241601189.png)
由升压变压器变压关系:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153824581653.png)
得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153824643611.png)
由升压变压器变流关系:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153824721614.png)
得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153824768533.png)
所以:(1)发电机的电动势:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824153824877848.png)
(2)发动机的输出功率
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241538250331045.png)
点评:难度中等,对于远距离输电的功率问题,要从能量守恒定律入手,对于匝数比的问题,线路上损耗的功率往往是该种类型题的突破口
![](http://thumb2018.1010pic.com/images/loading.gif)
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