问题 问答题

如图所示,A.B为相距较近的一对平行金属板,长度为l,间距为2d.一束相同的带电粒子(不计重力),以初速v0从A.B正中左端的O点射入A.B间,v0的方向与两板平行.如果在A.B间加上方向竖直向上、大小为E的匀强电场,则粒子束恰好从A板右端的a点射出;如果在A.B间加上方向垂直纸面向外、大小为B的匀强磁场,则粒子束将恰好从B板右端的b点射出.

(1)求E与B之比.

(2)如果同时加上上述的匀强电场和匀强磁场,粒子束是否沿直线OO’运动?若不是,它将向哪个方向偏转?

 

答案

((1)   (2) 粒子将向上偏转

、(1)加电场时,作类平抛运动,有

加磁场时,作匀速圆周运动,轨迹如图,(R-d)2+l2=R2,R=mv0/qB.

由以上各式解得

(2)若同时加上上述的电场和磁场,粒子刚进入时,受到的电场力大小为F=Eq,方向向上;受到的磁场力大小为F=Bqv0,由于,所以,因此粒子将向上偏转.

阅读理解

There are stories about two US Presidents,Andrew Jackson and Martin Van Buren,which attempt to explain the American English term OK. We don't know if either story is true,but they are both interesting.

The first explanation is based on the fact that President Jackson had very little education. In fact,he had difficulty reading and writing. When important papers came to Jackson,he tried to read them and then had his assistants explain what they said. If he approved of a paper, he would write “all correct” on it. The problem was that he didn't know how to spell. So what he really wrote was “ol korekt”. After a while,he shortened that term to “OK”.

The second explanation is based on the place where President Van Buren was born,Kinderhook,New York. Van Buren's friends organized a club to help him become president. They called the club the Old Kinderhook Club,and anyone who supported Van Buren was called “OK”.

小题1:The author ________.

A.believes both of the stories

B.doesn't believe a word of the stories

C.is not sure whether the stories are true

D.is telling the stories just for fun小题2:According to the passage,President Jackson ________.

A.couldn't draw up any documents at all

B.wasn't good at reading,writing or spelling

C. often had his assistants sign documents for him

D.didn't like to read important papers by himself小题3:According to the first story, the term “OK”________.

A.was approved of by President Jackson

B.was the title of some official documents

C.was first used by President Jackson

D.was an old way to spell “all correct”小题4:According to the second story,the term “OK” ________.

A.was the short way to say “Old Kinderhook Club”

B.meant the place where President Van Buren was born

C.was the name of Van Buren's club

D.was used to call Van Buren's supporters in the election

单项选择题