问题 问答题

阅读短文,回答下列问题,

分子或原子是构成物质材料的基元,基元中电子绕原子核的运转形成了电流,该电流产生的磁场,使每个基元都相当于一个微小磁体,由大量的基元组成一个集团结构,集团中的所有基元产生的磁场都同方向整齐排列,这样的集团叫做磁畴.

物体中含有大量的磁畴,但绝大多数的物体中,磁畴磁场的指向是杂乱无章的,结果使各个磁场几乎完全被抵消,所以,这些物体的磁性很弱,往往检测不到.

在铁块被磁化之前,众多磁畴磁场的指向是杂乱无章的,当被磁化后,一些磁畴产生的磁场和另一些磁畴产生的磁场都沿着相同的方向排列,这时,铁块就是有很强且持久的磁性.

在受到剧烈振动或高温下,磁畴磁场整齐排列的方向又会变成杂乱无章,使磁铁的磁性减弱,甚至消失.

(1)未被磁化的铁块没有磁性是因为磁畴磁场的指向______;

(2)为防止磁铁退磁,使用磁铁时应避免______、______;

(3)磁铁的磁场,本质上也是由______产生的.

答案

(1)由题意可知,物体原来不带电的原因是磁畴磁场的指向杂乱无章;

(2)在受到剧烈振动或高温下,磁畴磁场整齐排列的方向又会变成杂乱无章,使磁铁的磁性减弱,甚至消失;故磁铁应避免剧烈振动和高温;

(3)由题意可知,磁畴是由于电子绕原子核形成的,故磁场形成的本质是电流产生的;

故答案为:(1)杂乱无章;(2)高温、剧烈振动;(3)电流.

阅读理解

Perfect Disaster

All around us buildings shook. We decided to leave the town. We stopped once we had left the buildings behind us. The carts were moving in opposite directions, though the ground was perfectly flat, and they wouldn't stay in place even with their wheels blocked by stones.

In addition, it seemed as though the sea was being sucked(吸) backwards, as if it were being pushed back by the shaking of the land. Certainly the shoreline moved outwards, and many sea animals were left on dry sand.

Behind us were frightening dark clouds that opened up to show fire—like lightning, but bigger. Not long after that the clouds reached down to the ground and covered the sea. Now came the dust, though still thin. I looked back. A dense cloud appeared behind us, following us like a flood pouring across the land. Then a darkness came that was not like a moonless or cloudy night, but more like being in a closed and unlighted room. You could hear women and children crying, men shouting. Some were calling for parents, others for children; they could only recognize them by their voices.

Darkness and ashes came again, a great weight of them. We stood up and shook the ash off again and again; otherwise we would have been covered with it and crushed by the weight.

At last the cloud became thinner and thinner until it was no more than smoke or fog. Soon there was real daylight. The sight that met our still terrified eyes was a changed world, buried in ash like snow.

―from Pliny's letter to a friend

小题1:Pliny left the town after _____.  

A.the eruption

B.the sky became dark

C.the buildings began shaking

D.the sea went back小题2:The carts wouldn't stay still because _____.

A.the earth was shaking

B.the sea sucked them backwards

C.the wheels had stones under them

D.the lightening frightened the horses小题3:The reason why it was dark is that _____.

A.it was very late at night

B.clouds of ash covered the sun

C.there was a very bad storm

D.there was no moon that night小题4:People tried to find their relations by calling out their names and      .

A.listening to their voices

B.running about looking for them

C.shaking the ash off people

D.watching people as they ran past

单项选择题