问题 问答题

小李在一次实验中使用酒精灯,可是怎么也点不着,这是怎么回事呢?小李想探究个明白,于是进行了如下实验:①检查灯内是否还有足量的酒精,发现酒精量充足;②将灯内的酒精倒出少量点燃,能很好地燃烧;③挤压灯头处的灯芯,点燃挤出的一点液体,其不能燃烧;④将灯帽盖好放置几小时后,或直接在灯头上滴几滴酒精,酒精灯能正常燃烧;⑤去学校图书馆查阅了有关资料,记录了如下有关信息:酒精(学名乙醇)是元色透明、具有特殊香味的液体.它易挥发,能与水以任意比互溶,并能溶解多种有机物…实验室备用酒精一般是95%的工业酒精.酒精的沸点为78.5℃,水的沸点为100℃…

请回答下列问题.

(1)通过实验①能得出什么结论?

(2)小李设计进行实验②的目的是什么?

(3)实验③挤出的一点液体不能燃烧的原因可能是什么?

(4)通过以上探究活动,小李最终可以得出的结论是什么?

(5)实验④中,将灯帽盖好放置几小时后再点时,灯为什么便能正常燃烧?

(6)由此实验反思,实验时应该注意什么?

答案

(1)酒精灯不会被点燃,首先应该检查酒精是否用完了,若没有用完,则就是其他原因了,所以酒精灯没被点燃不是由于灯体内酒精量过少造成的;

(2)将灯内的酒精倒出少量点燃,看能否很好的燃烧,若能燃烧,则说明不是酒精灯内的酒精出了问题,所以目的是检查酒精灯内的酒精是否可以燃烧;

(3)挤压灯头处的灯芯,点燃挤出的液体,其不能燃烧,说明点燃的液体不是酒精,而是其它物质,因为酒精灯中的酒精是95%的工业酒精,酒精的沸点为:78℃,水的沸点:100℃,可见酒精比水更易挥发,所以酒精灯芯挤出的液体含酒精量非常低,故答案为:盖上灯帽后,酒精就不容易挥发,灯芯上水的含量不会增加,所以容易点燃;

(4)综合分析可知,酒精灯点不着的原因是:没有盖上灯帽,使得灯芯上的酒精挥发.故答案为:顶部灯芯处的酒精挥发,造成该处酒精中水的含量增高;

(5)从酒精没有挥发分析,盖上灯帽的原因是防止酒精挥发,灯芯上就不会留下较多水分,所以酒精灯就容易点燃;

(6)酒精灯用完后要及时盖上灯帽,防止酒精挥发和不易点燃.

故答案为:

(1)酒精灯没被点燃不是由于灯体内酒精量过少造成的;

(2)检查酒精灯内的酒精是否可以燃烧;

(3)顶部灯芯处的酒精挥发,造成该处酒精中水的含量增高;

(4)没有盖上灯帽,使得灯芯上的酒精挥发,灯芯处残留的水过多,所以点不着;

(5)防止酒精挥发,灯芯上就不会留下较多水分,所以酒精灯就容易点燃;

(6)酒精灯用完后要及时盖上灯帽.

单项选择题
阅读理解

Directions: Read the following passage. Answer the questions according to the information given in the

passage and the required words limit.

     Even plant can run a fever, especially when they're under attack by insects or disease. But unlike human,

plants can have their temperature taken from 3,000 feet away straight up. A decade ago, adopting the infrared

(红外线) scanning technology developed for military purposes and other satellites, physicist Stephen Paley

came up with a quick way to take the temperature of crops to determine which ones are under stress. The

goal was to let farmers precisely target pesticide (杀虫剂) spraying rather than rain poison on a whole field,

which invariably includes plants that don't have pest (害虫) problems.

     Even better, Paley's Remote Scanning Services Company could detect crop problems before they became

visible to the eye. Mounted on a plane flown at 3,000 feet at night, an infrared scanner measured the heat sent

out by crops. The data were transformed into a color-coded map showing where plants were running "fevers".

Farmers could then spot-spray, using 50 to 70 percent less pesticide that they otherwise would.

     The bad news is that Paley's company closed down in 1984, after only three years. Farmers resisted the

new technology and long-term backers were hard to find. But with the renewed concern about pesticides on

produce, and refinements (改进) ininfrared scanning, Paley hopes to get back into operation. Agriculture

experts have no doubt the technology works."This technique can be used on 75 percent of agricultural land

in the United States," says George Oerther of Texas A& M, who recently retired from the Department of

Agriculture, thinks remote infrared crop scanning could be adopted by the end of the decade. But only if Paley

finds the financial backing which he failed to obtain 10 years ago.

1. In what situation will plants have a fever? (No more than 8 words)

    ________________________________________________________________________________________

2. How can we apply pesticide spraying precisely? (No more than 10 words)

    ________________________________________________________________________________________

3. Why may infrared scanning technology by brought back into operation? (No more than 13 words)

    ________________________________________________________________________________________

4. What is the biggest problem that might prevent bringing infrared scanning technology back? (No more than

    7 words)

    ________________________________________________________________________________________