题干

物理课上老师做了下列实验(实验环境气压一个标准大气压).

⑴问同学借来一个用过的透明塑料袋,往里面滴入几滴酒精;

⑵把袋口扎紧;

⑶再放入80℃以上的热水中,发现塑料袋明显鼓起(如图);

⑷从热水中拿出鼓起的塑料袋,放入冷水中,发现塑料袋又变瘪了.

老师就说以上过程是因为酒精发生了________两种物态变化.但小明觉得操作(2)之前应该增加一个步骤:____,否则塑料袋鼓起来有可能是因为____这样实验结果就不准确了.

上一题 下一题 0.0难度 选择题 更新时间:2019-06-26 11:36:47

答案(点此获取答案解析)

汽化,液化,将塑料袋挤瘪尽量排出空气,空气的热胀冷缩

同类题2

阅读下面材料,在空白处填入适当的内容(1个单词)或括号内单词的正确形式。

             A mong all the fast growing science and technology, the research of human genes, ____biological engineering as people call it, is drawing more and more attentionnow. Sometimes it is a hot topic ____(discuss) by people.

          The greatest thing that gene technology can do is to cure serious diseases thatdoctors at present can almost do nothing with, such as cancer and heartdisease. Every year, millions of people are murdered by these two ____(kill).And to date, doctors have not found ____ effective way to cure them. But if thegene technology ____(apply) , not only these two diseases can be curedcompletely, ____(bring) happiness and more living days to the patients, butalso the great amount of money people spent on curing their diseases can besaved, so ____ benefits the economy as well. In addition, human life span(寿命) can be prolonged.

         Gene   technology can help people to give birth to more healthy and clever children.Some families, with the English imperial(皇室)family being a good example, have hereditary diseases. This means theirchildren will for sure have the family disease, ____ is a great trouble forthese families. In the past, doctors could do nothing about hereditarydiseases, ____ gene technology can solve this problem ____(perfect). Thescientist just needs to find the wrong gene and correct it, and a healthy childwill be born.