问题 问答题 简答题

什么叫磁感应强度?如何用公式表示?

答案

参考答案:

①磁感应强度是表示磁场中某点磁场强弱和方向的物理量,它是一个矢量。

②公式:B=△Fl(I△L)。式中:△L—与磁场方向垂直的很小的一段导线长度,m;l—通过导线的电流,A;△F——长度为△L的导线通以电流I时,在磁场中所受的力,N。B的单位为特斯拉(T)。

阅读理解

阅读理解。

    Round eyes, round head, round ears, round body! What is this lovely little animal?

    He looks like a bear. But he is not a bear. He's a KOALA.

    People in Australia love koala and take care of them. They have set up places for them to live safely. No

one can kill them for their pretty fur (毛片). When a koala is born,he has no fur. And he is not as big as

your little toe (脚趾)! The mother koala has a pocket in the front of her body. The baby goes into this warm

pocket. There he stays for six months.

    When the baby leaves the pocket, he has much fur. And he is about as big as your shoe. He climbs to his

mother's back. He rides there while she teaches him how to find food. Mrs. Koala is a loving mother. She

takes good care of her baby. But when he is bad, she beats him! The baby cries just as a small child does.

If he keeps on crying, his mother beats him again. When he stops crying, she takes him in her arms. And

then they both go to sleep for a while.

    The koala could not live without a special kind of tree. The tree gives him both his home and his food.

For most of the day the koala sleeps in the tree.

    At night the koala looks for food. He may go miles to find it. He likes only the bark (树皮) and the leaves

of the tree. He eats nothing else. And he eats more than two pounds each night!

    How lovely the koalas really are!

1.People in Australia ______. [ ]

A.keep koalas in their home

B.put koala in the tree

C.set up places for koalas to live safely

D.raise baby koalas in their pockets

2.After his born, the baby koala lives in his mother's pocket ______. [ ]

A.for six days

B.for six months

C.for a night

D.all his life

3.What does the mother koala usually do when her baby is bad? [ ]

A.She takes him in her pocket.

B.She keeps him on her back.

C.She makes him cry.

D.She beats him.

4.Koalas cannot live without a special kind of tree because ______. [ ]

A.they have to keep cool under the tree

B.they eat the fruit on the tree

C.they stay in the tree all the time

D.they live in the tree and get food from it

5.What is the text mainly about? [ ]

A.How people in Australia protect koalas.

B.Lovely koalas in Australia.

C.Koalas cannot live without a special kind of tree.

D.The way mother koalas take care of their babies.

名词解释