问题 选择题

如图所示,在半径为R的圆内有一磁感应强度为B的向外的匀强磁场,一质量为m、电量为q的粒子(不计重力),从A点对着圆心方向垂直射入磁场,从C点飞出,则下列说法不正确的是(  )

A.粒子带正电

B.带电粒子从C点飞出时,偏转角为60°

C.粒子的轨道半径为R

D.粒子在磁场中运动的时间为

πm
3Bq

答案

A、带电粒子沿半径方向入射,如图可知,经过磁场偏转60°后又沿半径方向出射,从而画出圆弧对应的弦,确定圆弧的圆心,根据左手定则可知,粒子带正电,故A正确;

B、带电粒子沿半径方向入射,如图可知,经过磁场偏转60°后又沿半径方向出射,故B正确;

C、带电粒子沿半径方向入射,经过磁场偏转后又沿半径方向出射,从而画出圆弧对应的弦,确定圆弧的圆心,根据几何关系可知,r=Rtan60°=

3
R.故C错误;

D、带电粒子沿半径方向入射,经过磁场偏转60°后又沿半径方向出射,从而画出圆弧对应的弦,确定圆弧的圆心,算出圆心角θ.再根据周期公式T=

θ
t,则运动的时间为
πm
3Bq
.故D正确;

本题选择不正确的,故选:C

阅读理解

E

Humans are naturally drawn to other life forms and the worlds outside of our own. We take delight in the existence of creatures and even whole socicties beyond our everyday lives.

This sense of wonder is universal look at the efforts that scientists have made to find out whether life of some kind exists on Mars, and the popularity of fantasy(幻想) litcrature or movies like The lord of the Rings, This sense of wonder drous us to each other, to the world around us, and to the world of make-believe. But have we gone to far in creating worlds of fantasy that we are missing the phcasure of other worlds that alrewly exist all around us?

Human beings, as biologists have suggested, possess an inborn desire to connect with and understand other life forms, However, people, especially in big cities, often lead rather isolated lices. In a study of British schoolchildren, it was found that children bye age eight were much more familiar with hurmans for television shows and cideo games than with common wildlife. Without modern technology ,a amall pond could be an amazing world filled with strange and beautiful plants, insects,birds,and animals. When we lack meaningful interaction (交互) with the world around us, and sometimes ecen with our families and friends , we seek to understand and communicate with things that exist only in our imaginations or on a computer screen

The world of make-believe is not neccsanly bad, But when the world of  famsity becomes the only outlet (出路) our sense of wonder ,then we are really missing something, We are missing a connection with the living world. Other wonderful worderful worlds exist all around us. But even more interesting is that if we look closely enough ,we can see that these worlds, in a broad sense , are really part of our own.

72.The popularity of  The Lord of the rings proves     

A.the close connestion between man and the fantasy world

B.the wonderful achievements of fantasy literature

C.the fine taste of moviegoers around the world

D.the general existence of the sense of curiosity

73.What can we infer from the underlineed sentence in Paragraph 3?

A.People are fra less familiar with the world of fantasy.

B.The world around us could serve as a sound of  wonder.

C.The world of fantasy can be mirred by  a small and lively pond.

D.Modern technology prevents us from developing our sense of wonder.

74. If our sense of wonder relics totally on the world of make-believe. we will_______.

A.fail to appreciate the joy in our lives

B.be confused by the world of make-believe

C.miss the chance to recognizc the fantas world

D.be tranped by other worlds exsting all around us

75. What is the main purpose of the passage?

A.To show us the hidden beauty in our world.

B.To warn us not to get lost in the fantasy wonder

C.To argue against the misuse of the sense of wonder

D.To discuss the influence of the world of make-believe

单项选择题