题干

小明同学从玩具电动机中拆下一段细铜丝(漆包线),经测量长度为 h 米。

他想进一步测量其体积,家里没有量筒,身边的测量工具仅有毫米刻度尺,怎样用刻度尺测量其体积呢?请你帮助他写出实验步骤,并列出计算方法。(测量所得的结果可以用字母表示)。

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答案(点此获取答案解析)

①把铜丝线紧密缠绕到铅笔上,一共缠 n 匝。②用刻度尺测量出 n 匝的长度是 L。③计算铜丝的半径 r =L/2n④计算铜丝的底面积:S=π×r2=π×L2/4n2⑤计算漆包线的体积:V=Sh =πhL2/4n2

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    People who do not get enough vitamin A in their diet may develop night blindness. But in the developing world, a lack of vitamin A causes much more serious harm to children. The world Health Organization links the lack of vitamin A to as many as 250,000 child deaths every year.

    One excellent source of vitamin A is found in newly developed sweet potatoes with orange flesh. Orange sweet potatoes contain high levels of beta-carotene, which the body changes into vitamin A. Experts say orange sweet potatoes could help the Africans who are lacking in vitamin A. But, first, more people will need to be persuaded to eat them. Sweet potatoes need a better image in Africa. Jan Low with the International Potato Center says, “We do have an image problem with sweet potatoes. In many African countries, they are seen as a crop of the poor.”

    Ms. Low explains that sweet potatoes are mainly grown by poor women to feed their families in case another crop fails. The sweet potatoes commonly grown in Africa have white or yellow flesh. But they are low in vitamin A.

    Jan Low took part in a project to study how to market orange sweet potatoes to Africans best. She worked on an information campaign(活动) in Mozambique and Uganda. The campaign included radio messages about the nutritional(营养的) benefits of the orange sweet potato. They advertised its ability to “fight diseases, make you strong, clear you skin and make you look healthy”. In areas without radio, the campaigners spread the message through theater. The performances included singing, dancing and storytelling. And everywhere they went, the campaigners wore orange T-shirts and hats. They even drove orange cars.

    Dan Gustafson heads the Washington office of the United Nations Food and Agriculture Organization. He mentions the efforts in the past to increase the popularity of other nutritious crops. He says most of these efforts failed because organizers of the campaigns did not consider what people wanted to eat. People want to eat what they are familiar with. But Mr. Gustafson sees a better chance for the efforts to increase the popularity of the orange sweet potato in Africa. Except for the color, the orange sweet potato is almost the same as what people already eat. Dan Gustafson says, “I think this time the campaigners will succeed, because they have made enough advertisements and the difference between the vegetable they have advertised and what people already eat is not a radical one.”