问题 选择题

如图所示,匀强磁场的磁感强度B=2.0T,指向x轴的正方向,且ab=40cm,bc=30cm,ae=50cm,通过面积S(aefd)的磁通量Φ为(  )

A.0

B.0.24Wb

C.0.18Wb

D.0.3Wb

答案

面积S(aefd)与匀强磁场方向的夹角未知,因此可将面积S(aefd)投影到与x轴垂直的abcd上,aefd的有效面积就是abcd的面积,

所以穿过矩形线圈的磁通量是Φ=BS=2.0×0.4×0.3=0.24Wb,因此ACD错误;B正确;

故选:B

阅读理解

Many people go to school for an education. They learn languages, history, geography, physics, chemistry and mathematics. Others go to school to learn a skill so that they can make a living. School education is very important and useful. Yet no one can learn everything from school. A teacher, no matter how much he knows, cannot teach his students everything they want to know. The teacher’s job is to show his students how to learn. He teaches them how to read and how to think. So, much more is to be learned outside school by the students themselves.

It is always more important to know how to study by oneself than to memorize (记住) some facts or a formula (公式). It is usually quite easy to learn a certain fact in history or a formula in mathematics. But it is very difficult to use a formula in working out a maths problem. Great scientists, such as Einstein, Newton and Galileo didn’t get everything from school. But they were all so successful. They invented so many things for mankind.   Above all, they knew how to use their brains.

小题1: Whether he is more ________or less, a teacher can’t teach his students everything they want to know.

A.important

B.useful

C.difficulty

D.knowledgeable (有知识的)小题2:A teacher’s job is mainly to train his students to master the ability of __________.

A.learning by themselves

B.making a living

C.reading and thinking

D.studying all the subjects小题3: The reason for scientists’ success is that _______.

A.they read books that were not taught at school

B.they worked all their lives

C.they wasted not a single moment

D.they knew how to use their brains

单项选择题