题目内容
(8分)如图所示,电源电动势为E=20V,内阻r=1
,一个“8V,16W”的电灯与一个电动机串联在电源上,电动机线圈内阻为r0=2
,已知在电键闭合后电灯能正常发光,求:
(1)电动机两端电压U
(2)电动机输出的机械功率
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241306003131383.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130600157333.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130600157333.png)
(1)电动机两端电压U
(2)电动机输出的机械功率
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241306003131383.png)
(1)10V(2)12W
(1)电灯正常发光,由P=UI得,电流I=![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130600422828.png)
由闭合电路欧姆定律知:E=U灯+U+Ir
U="E-" U灯- Ir=20-8-2
1=10V
(2)电动机总功率P=UI=10
2=20W
热功率P热=I2r0=22
2=8W
机械功率为P机=P-P热=12W
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130600422828.png)
由闭合电路欧姆定律知:E=U灯+U+Ir
U="E-" U灯- Ir=20-8-2
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130600453214.png)
(2)电动机总功率P=UI=10
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130600453214.png)
热功率P热=I2r0=22
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130600453214.png)
机械功率为P机=P-P热=12W
![](http://thumb2018.1010pic.com/images/loading.gif)
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