问题 实验题

为了探究给物质加热方法,某同学做如下实验:取三支试管,各加入3 mL水。1号试管的底部放在酒精灯上方约3 cm处加热;2号试管的底部与酒精灯灯芯接触加热;3号试管的底部放在酒精灯外焰部分加热。记录上述三种情况下将水加热至沸腾时所用的时间,分别是60s、35s、27s。

请你完成下列问题:

(1)分析上述实验结果,你认为给物质加热时应该用酒精灯哪一层火焰?为什么?

(2)加热试管里的液体时,要注意什么问题?(至少答出三点)

(3)在加热时,操作不当常常引起试管炸裂,请和其他同学交流总结可能的原因。

答案

(1)外焰部分,因为用外焰加热同样多的水至沸腾所用时间最短,说明外焰温度最高。

(2)液体体积不要超过试管容积的1/3,试管夹应夹在试管口1/3处,试管要倾斜,与桌面成45°角,管口不准对着有人的地方,要先预热再集中加热。

(3)加热时试管外壁有水未擦干,试管底部接触了灯芯,没有先对试管进行预热就集中在试管底部加热。

双选题
阅读理解

Just how far does the euro(欧元) have to fall before Europe actually becomes reasonable?

Anyone traveling to the old continent from the U.S. in recent years has learned the hard way how expensive it is. The situation has improved in the last couple of months, thanks to the Greek financial crisis. But it still has a way to go.

Alarm about Greece—and other financially unstable countries in Europe—has dragged down the euro sharply. In November, before the crisis struck, you needed about $1.49 to buy one euro. Today you need only about $1.36. That's a 9% cut.

What does that mean for you, the would-be traveler? It's a big sale.

As recently as November, when the euro was flying high, the OECD estimated that countries like France, Italy and Germany were about a third more expensive than the U.S. Not all European countries were quite as expensive for the American visitor: Greece only cost about 17% more than the US, while the Czech Republic (which is not part of the eurozone) was actually about 15% cheaper than back home.

Fast-forward two months, and the situation looks somewhat better.

At current exchange rates, places like France will still cost you about 23% more than the U.S., but cheaper countries such as Spain and Greece are now only about 6% more expensive. The Czech Republic's a fifth cheaper than the U.S.

European prices will only break even(持平) with the U.S. if the euro falls to about $1.10, says the OECD. But is it going to get there?

Greece's financial crisis may or may not be over. Members of a labor union just occupied part of the finance ministry to protest against the planned austerity(紧缩) measures. No, it doesn't inspire confidence!

Julian Jessop, chief international economist at the Capital Economics consultancy in London, sees the euro falling to $1.25 by year-end. “We still think the euro should be a lot lower,” he says. “We think the outlook for the European economy is a lot worse than for the U.S. And Greece is only a symptom of a wider problem: Does the eurozone make sense as a currency union?” If he's right, you may want to wait to change your money or book a trip.

67.   In the passage the writer offers some suggestions to the travellers from______.

A.USA           B.Europe             C.Greece             D.China

68.   The underlined word “it” in the passage refers to ______.

A.the planned austerity measures

B.Greece’s financial crisis

C.the protest from a labor union

D.the decline of the euro in value

69.   Julian Jessop has a negative attitude toward the euro because he thinks ______.

A.Greece’s financial crisis may not be over

B.the euro will drop to $ 1.25 by the end of the year

C.the European economy is a lot worse than the US’

D.the other European countries have a similar problem like Greece

70.   The purpose of the author writing the passage is to tell the readers that ______.

A.the euro shall be further reasonably lowered

B.travelers to Europe will save less in the future

C.the economic situation in Europe is worsening

D.the Greek financial crisis influences the whole Europe