问题 选择题

如图所示,a.b直线分别表示由两种材料制成的两条长度相同,粗细均匀的电阻丝甲乙的伏安特性曲线,下列判断中正确的是(  )

A.a代表的电阻丝较粗

B.b代表的电阻丝较粗

C.两根电阻丝的阻值相等

D.图线表示的电阻丝的阻值与流过的电流成正比

答案

A、B、C导线的电阻R=

U
I
,由数学知识知:图线斜率的倒数表示电阻,图线a的斜率小于b的斜率,所以a的电阻大于b的电阻,根据电阻定律R=ρ
L
S
得知,长度相同,材料相同,a的横截面积小,b的横截面积大.故A、C错误,B正确.

D、电阻的大小与电压、电流无关.它是比值定义的,故D错误.

故选B.

解答题
阅读理解

阅读理解。

     Women have jumped ahead of men for the first time in using the Internet to do their holiday shopping,

according to a study published last week in the US.

     For Years men have been more likely to shop on the Internet than women, but during the 2011 holiday season 58 percent of those making online purchases(购买) were women.

     "It shows how mainstream the Internet is becoming", said Lee Rainie, director of the Pew Internet and American Life Project group, which carried out the study.

      Rainie said it was only a matter of time before women shoppers caught up with men. This is because

women traditionally make decisions about spending.

      Users were more likely to shop online to save time. Internet users between the ages of 18 and 29

were responsible for some of the most dramatic increases in the online gift-buying population this time

around.

      However, three-quarters of the US Internet users did not buy holiday gifts online in 2011. They

worried about credit card security(安全), or just compared online prices with off-line prices, then

dashed off to the shops to get the best deals.

     "But even if shoppers don't buy online, websites are becoming promotion tools for stores," said Dan

Hess, vice president of Comscore Networks Inc. Hess said that actually most stores' websites can make

customers fully believe the security of their credit card numbers. And most are able to ensure that gifts

arrive on time. "It's all about making the shopping experience more efficient, more reliable and more

comfortable." Hess said.

1. Which of the following statements is true?

A. More women shopped online than men in 2011.

B. There were fewer women online shoppers than men in 2011.

C. Most of the Internet users between the ages of 18 and 29 are women.

D. People in the US were more likely to buy gifts online.

2. From the passage we can infer that________.

A. men usually decide how to spend money in the family  

B. women usually decide what to buy in the family

C. the Internet is used in all the shops.                

D. more and more shops will sell their goods online.

3. According to Dan Hess, shopping online is ___________.

A. unsafe

B. convenient

C. a waste of time

D. cheaper

4. What can we know from the passage?

A. American people only buy gifts in holidays.  

B. Shopping online is fun for women.

C. Shopping off-line provides better service.  

D. Young people like to do gift-shopping online.