问题 选择题

关于电流,下列说法中正确的是(    )

A.导线内自由电子的定向移动速率等于电流的传导速率

B.电子运动的速率越大,电流越大

C.电流是一个矢量,其方向就是正电荷的定向移动方向

D.在国际单位制中,电流是一个基本物理量,其单位“安培”是基本单位

答案

答案:D

题目分析:A、导线内自由电子的定向移动速率,一般为10-5m/s的数量级,电流的传导速率等于光速;错误

B、由电流微观表达式可知,电子运动的速率越大,电流不一定越大;错误

C、电流随有方向,但是电流求和是代数求和,则电流为有方向的标量;错误

D、在国际单位制中,电流是一个基本物理量,其单位“安培”是基本单位;正确

故选D

点评:注意区分电子定向移动速率、电子热运动速率和电流传导速率。

阅读理解

阅读理解

    "Who needs  a  shopping mall (购物中心 ) if you have Taobao?" says Wang Lin,28,a writer in

Beijing. Taobao ,China's largest online shopping site(网上购物网站),has become an important part

of Wang Lin's life. She spends lots of money on Taobao. A growing number of Chinese Internet users

like Wang have found the joys of online shopping. Most online shoppers are students or young workers. More women shop on line than men. Clothing and home-use products are the most popular on line. It

was reported that more than 250 billion yuan, was spent on online shopping last year,80% through

Taobao. Taobao means "looking for treasure" in Chinese. People can find almost everything they need

on Taobao,from clothes to books,from candies to DVD players. " You may question the security of

online shopping," Wang Lin said,"It's very safe and convenient. Unless you receive the products from

the sellers and are satisfied with them,the shop owner will not get the money. You can also get your

money back if you want to return the products. "

1. What are the most popular on line? 

A. Candles and DVD players.

B. Clothes and books

C. Clothing and home-use products

2. Taobao is       .

A. a shopping mall

B. an online shopper

C. an online shopping site

3. Most online shoppers are          .

A.young

B.old

C.babies

4.What does the underlined word "security" mean?

A.质量

B.安全

C.信誉

5. Which  is the best title (标题) of the passage?

A. Wang Lin's life

B. Online shopping in China

C. Shopping on line is not safe

多项选择题