题目内容
如图4-3所示,是用直流电动机提升重物的装置,重物质量
,电源电动势
,内电阻
,电动机的内电阻
。阻力不计。当匀速提升重物时,电路中电流强度
。取
,试求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241137371933080.gif)
小题1:(1)电源的总功率和输出功率;
小题2:(2)重物上升的速度。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113737052461.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113737083318.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113737130291.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113737146396.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113737161256.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113737161475.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241137371933080.gif)
小题1:(1)电源的总功率和输出功率;
小题2:(2)重物上升的速度。
小题1:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113737208983.gif)
小题2:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241137372241027.gif)
电源输出的总能量,一部分消耗于自身内阻,其余全部输出传给电动机。电动机获得的电能,一部分转化为电动机的内能,其余的全部转化为机械能。
(1)电源的总功率为:![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113737239739.gif)
电源的输出功率为:![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113737208983.gif)
(2)电动机的输入功率为:![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113737255522.gif)
电动机的热功率:![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113737286755.gif)
电动机的输出功率等于它对重物做功的功率,即![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113737286526.gif)
所以,
(1)电源的总功率为:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113737239739.gif)
电源的输出功率为:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113737208983.gif)
(2)电动机的输入功率为:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113737255522.gif)
电动机的热功率:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113737286755.gif)
电动机的输出功率等于它对重物做功的功率,即
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113737286526.gif)
所以,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241137373021027.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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