问题 选择题

李慧同学为了测一只正在煲粥的电饭煲的实际电功率,她关闭了家中其他所有家用电器,这时她家标有“3000revs/(kW•h)”字样的电能表的转盘每分钟转过15圈,则这只电饭煲当时的实际电功率为(  )

A.15W

B.200W

C.300W

D.3000W

答案

这只电饭煲在1分钟内消耗的电能:W=

15r
3000r/kW•h
=0.005kW•h,

这只电饭煲当时的实际电功率:P=

W
t
=
0.005kW•h
1
60
h
=0.3kW=300W.

故选 C.

单项选择题
单项选择题

My Space and other Web sites have unleashed a potent new phenomenon of social networking in cyberspace, (1) at the same time, a growing body of evidence is suggesting that traditional social (2) play a surprisingly powerful and under-recognized role in influencing how people behave.

The latest research comes from Dr. Nicholas A. Christakis, at the Harvard Medical School, and Dr. James H. Fowler, at the University of California at San Diego. The (3) reported last summer that obesity appeared to (4) from one person to another (5) social networks, almost like a virus or a fad. In a follow-up to that provocative research, the team has produced (6) findings about another major health (7) : smoking. In a study published last week in the New England Journal of Medicine, the team found that a person’s decision to (8) the habit is ply affected by (9) other people in their social network quit—even people they do not know. And, surprisingly, entire networks of smokers appear to quit virtually (10)

For (11) of their studies, they (12) of detailed records kept between 1971 and 2003 about 5,124 people who participated in the landmark Framingham Heart Study. Because many of the subjects had ties to the Boston suburb of Framingham, Mass. , many of the participants were (13) somehow—through spouses, neighbors, friends, co-workers—enabling the researchers to study a network that (14) 12,067 people.

Taken together, these studies are (15) a growing recognition that many behaviors are (16) by social networks in (17) that have not been fully understood. And (18) may be possible, the researchers say, to harness the power of these networks for many (19) , such as encouraging safe sex, getting more people to exercise or even (20) crime.

1()

A.so

B.but

C.as

D.although