问题 填空题

一束质量为m、电量为q的带电粒子以平行于两极板的速度v0进入匀强电场,如图所示,如果两极板间电压为U,两极板间的距离为d,板长为L,设粒子束不会击中极板,则粒子从进入电场到飞出极板时电势能的变化量为______(粒子的重力忽略不计)

答案

粒子在电场中做类平抛运动,根据牛顿第二定律与运动学公式可得,经过电场后的偏转位移y=

1
2
at2=
1
2
qU
md
(
L
v0
)2

而电场中,电势能的变化量等于电场力做功的多少,即△E=W=qEy=q

U
d
y

由以上两式,综合而得,飞出极板时电势能的变化量为

q2U2L2
2md2
v20

故答案为:

q2U2L2
2md2
v20

阅读理解

阅读理解。

      Computer technology (技术) has become an important part of people's life. This technology has its

own special words. One well-known computer word is Google. It is the name of a popular "search engine

(引擎)" for the Internet.

      People use the search engine to find information about almost any subject on the Internet. The people

who started the company named it Google because in math Google is a very large number-one hundred

zeros follow the number one. When you "Google" a subject, you can get a lot of information about it.

      If you Google someone, you might find that person's name on a blog. A blog (博客) is short for a Web

log. It is a personal Web page. Some people write blogs to express their opinions and ideas over the Internet.

Some use them to share their lives with faraway friends or family. Others write blogs to help them deal with

sickness, money problems or to choose movies to see or books to read. Some people add information to their

blogs every day. People who have blogs are called bloggers.

根据短文内容,判断句子的正(T)误(F)。

( )1.Google and Blog are two kinds of popular search engine.

(     )2.One can use Google to search the Internet for all information he wants.

(     )3.People may use Google to share their opinions or ask others for help.

(     )4.Bloggers should add information to their blogs every day.

(     )5.From the passage we can infer (推断) that computer technology is changing people's life.

单项选择题