问题 问答题 简答题

影响漏磁场强度的因素有哪些,为什么漏磁只能检测铁磁性材料?

答案

参考答案:

影响缺陷漏磁场的因素有:材料的此特性、磁化强度以及缺陷本身的性质,如缺陷的形状、大小、深度、走向等。

漏磁检测只是针对铁磁性材料。因为非铁磁性材料的磁导率约等于1,与所处环境的磁导率基本相同,这样缺陷周围的磁场就不会因为磁导率变化而变化,从而也就不会产生漏磁场。

阅读理解

阅读理解

     In Yemen, you always see one type of vehicle on the road:the water truck.They travel mountain roads

and cross deserts to bring Yemenis the goods more valuable than oil.It is one that only the rich can afford, with the supply regularly  being cut off.Others must rely on scarce rain or charity to  fight thirst.

     Experts say Yemen is going to be the first country in the world to run out of water.The capital, Sanaa, will run out of drinking water as early as 2025, says a report by the World Bank.

     Hannan, an 18yearold from Lahej, said that only the rich could prepare for cuts in supply."In a good

week we'll have a water supply all week but then the following week there will be water only for a day or

two, " she said.

     She and her husband, a factory worker, pay 3,000 riyals (99 yuan) for a week's supply of water

from a touring water  truck when the taps run dry.With an income of only 20,000 riyals (660 yuan) a

month, this means the family often spend half their money on water.

     "There are a lot of people who can't afford it and they have to rely on their neighbors to help, " she

said.

     The average person in Yemen survives on onefifth of what the World Health Organization considers

to be enough water.

     In Taiz, in the south, tap water is available only once every 45 days.In the mountainous Malhan district

in the north, women and children climb a 1,500m mountain to collect water from a spring, often in the

small hours to avoid long queues.

     Yemen is located in Southwest Asia, bordering the Arabian and Red Sea.Yemeni people have lived

on scarce water supplies for thousands of years but that problem has been made serious by conflict in the

area, the fastgrowing population and the use of water to grow a drug called qat.With one of the world's

highest rates of population growth-3.46 percent, Yemen is the poorest Arab country.

     The government is considering desalinating (淡化) seawater, but this would be expensive and it may

now be too late.The only other solution is to cut down on farming, but that means importing even more

food.

1. The passage aims to________.

A. analyze the reasons why Yemen lacks water

B. suggest some solutions to the water issue in Yemen

C. present how serious the water problem is in Yemen

D. encourage the world to help Yemenis who are suffering from water shortages

2. When Hannan said that only the rich could prepare for cuts in supply, she meant that________.

A. rich people drank more water than the poor

B. rich people could buy water from the water trucks if there was a water supply cut

C. she had a rich neighbor who often helped her during water supply cuts

D. the rich were not affected by water supply cuts

3. Which of the following may be a reason why Yemen is short of water?

A. The country has had no rain for a long time.

B. The population of Yemen is growing fast.

C. The government has failed to reduce farming.

D. People can't afford the water from government water trucks.

4. The best title for the passage is "________".

A. Never take water for granted

B. The water truck-the commonest sight in Yemen

C. The first country to run out of water in the world

D. No water for Yemen

单项选择题