问题 选择题

如图1所示,理想变压器原、副线圈匝数比为10:1,R1=20Ω,R2=30Ω,C为电容器.已知通过R1的正弦交流电如图2所示,则(  )

A.交流电的频率为0.02HZ

B.原线圈输入电压的最大值为200

2
V

C.电阻R1的电功率约为10W

D.通过R2的电流始终为零

答案

A、根据变压器原理可知原副线圈中电流的周期、频率相同,周期为0.02s、频率为50赫兹,A错.

B、由图乙可知通过R1的电流最大值为Im=1A、根据欧姆定律可知其最大电压为Um=20V,再根据原副线圈的电压之比等于匝数之比可知原线圈输入电压的最大值为200V,B错误;

C、根据正弦交流电的峰值和有效值关系可知电阻R1的电流有效值为I=

Im
2
=
1
2
A,电阻R1的电功率为P=I2R1=10W,故C正确;

D、因为电容器有通交流、阻直流的作用,则有电流通过R3和电容器,D错误;

故选C.

阅读理解

It is not only experts in China who are arguing over whether women should work after marriage or not. Worldwide this question is being discussed as an interestingly large number of married women enter the workplace. Take the United States for example. Since 1960, the percentage of married women in the work force has jumped from 31.9 per cent to 59.4 per cent.

American women first moved into the paid labour force during the World War II, when men left their jobs to fight. In the last fifty years, more and more women have worked outside the home. And over these years of developing, Americans have changed their social values as a result. In 1975, women aged 35 and above made up half of all working women. And by 1980, 60 per cent were women at the age of 45 and above.

Now in Japan, women’s work group is M-shaped with middle-aged women and those aged 20-25 at the two peaks. According to statistics(统计), 37.7 per cent of Japanese women at childbearing age(25-29) still engaged themselves in work in 1980. and the number reached 50 per cent the next year.

Being a housewife has always been regarded as a “graceful occupation” in Japan. Some young Japanese women believe it is good to be a “ professional housewife”. However, old attitudes have been changing everywhere, and sometimes just out of economic necessary. In recent years, a great number of city housewives have poured out of homes to take part time jobs. Even the UN has given its support.. The 34th Congress of the United Nations in 1979 put forward the decision for formal agreement on the getting rid of discrimination(歧视) against women.

So far, most UN members have agreed on it, but some still haven’t,  including the United States.

小题1:From the first passage, we can learn that ________________.

A.experts encourage women to take paying jobs.

B.men encourage women to take paying jobs

C.government encourage women to take paying jobs.

D.more and more people begin to care about women’s life小题2:In the United States _________________.

A.married women are lazier than their husbands.

B.Husbands are lazier than their wives

C.Few married women used to work outside

D.More married women used to work outside小题3:Married women in Japan________________.

A, all work outside their homes     

B. seldom work outside their homes

C. have different opinions on their working outside 

D. all do housework at their homes

小题4:More and more women have taken jobs outside for the reason that ____________.

A.they have no children to take care of

B.they have no housework to do

C.they want to make more friends

D.they want to improve their living conditions

问答题