问题 选择题

如图11所示,在平面直角坐标系中有一个垂直于纸面向里的圆形匀强磁场,其边界过原点O和y轴上的点a(0,L).一质量为m、电荷量为e的电子从a点以初速度v0平行于x轴正方向射入磁场,并从x轴上的b点射出磁场,此时速度方向与x轴正方向的夹角为60°.下列说法中正确的是         (  )   

A.电子在磁场中运动的时间为

B.电子在磁场中运动的时间为

C.磁场区域的圆心坐标()

D.电子在磁场中做圆周运动的圆心坐标为(0,-2L)

答案

BC

由图可以计算出电子做圆周运动的半径为2L,故在磁场中运动的时间为t=,A错,B正确;ab是磁场区域圆的直径,故圆心坐标为(L,),电子在磁场中做圆周运动的圆心为O′,计算出其坐标为(0,-L),所以C正确,D错误.

阅读理解

阅读理解。

    Recently, children's literature (文学) has become more and more popular. In fact, children's literature

has been welcomed by both children and adults. People have tried to find out why adults love children's

literature just like children themselves. But there is no final answer.

    Children's literature is very different from adult's literature. Most of it is fantasy (幻想). That means

children can use their imagination. They can enjoy the fantasy world, which is never boring. The most

important thing is that the world is bright and hopeful. In the fantasy world, dead people can be alive again

and broken legs can grow once more. Right always beats wrong in the end. 

    Children's literature can also influence children a lot in education. When they read, their knowledge is

increased and children know more about the truth. For a child who just learns to read, understanding the

meaning of a word may be greater than learning the word itself.

    Children's literature is not only for children. A large number of adults like it too. Not only young adults,

parents and teachers, but also other people of all ages enjoy it. Both children and adults who love children's

literature can get much pleasure from it.

根据短文内容回答问题。

1. Is children's literature becoming more popular now?

                                                                                                                                   

2. What's the fantasy world like?

                                                                                                                                   

3. What does the sentence "Right always beats wrong in the end" mean in Chinese?

                                                                                                                                    

4. How does children's literature influence children in education?

                                                                                                                                    

5. How do the people feel when they read children's literature?

                                                                                                                                    

选择题