题目内容
如图所示,粗细均匀的U型玻璃管竖直放置,左端封闭,右端开口且足够长,开始左端空气柱长20cm,两管水银面等高.从右侧管口缓慢加入水银,左管内气柱长变为15cm.温度不变,大气压强为p0=75cmHg.
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250012211862045.jpg)
①加入水银的长度;
②此过程封闭气体吸热还是放热,并说明理由.
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250012211862045.jpg)
①加入水银的长度;
②此过程封闭气体吸热还是放热,并说明理由.
①35cm ②放热
试题分析:①以左端封闭气体为研究对象,设末状态右侧管内水银面比左侧高h,
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001221202428.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001221217594.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001221217773.png)
加入的水银柱长为x,
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001221233760.png)
解得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001221248435.png)
②由于气体温度不变,所以内能不变,外界对气体做正功,根据热力学第一定律
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001221264692.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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