问题 选择题

利用如图7所示的电流互感器可以测量被测电路中的大电流,若互感器原、副线圈的匝数比n1∶n2=1∶100,交流电流表A的示数是50 mA,则                    (  )

A.被测电路的电流的有效值为5 A

B.被测电路的电流的平均值为0.5 A

C.被测电路的电流的最大值为5A

D.原、副线圈中的电流同时达到最大值

答案

AC

交流电流表示数为副线圈中电流的有效值,即I2=50 mA=0.05 A,根据得,I1=5 A,A正确B错误;原线圈(被测电路)中电流的最大值I1mI1=5A,C项正确;原线圈中电流最大时,线圈中磁通量的变化率等于零,此时副线圈中的电流最小;原线圈中电流等于0时,磁通量的变化率最大,副线圈中电流最大;所以原、副线圈中的电流有相位差,故不能同时达到最大值,D项错误.

阅读理解

阅读理解

    The garden city was largely the invention of Ebenezer Howard (1850-1928). After immigrating from

England to the USA, and an unsuccessful attempt to make a living as a farmer, he moved to Chicago,

where he saw the reconstruction of the city after the disastrous fire of 1871.In those days, it was

nicknamed "the   Garden City",almost certainly the source of Howard's name for his later building plan

of towns.Returning to  London, Howard developed his design in the 1880s and 1890s, drawing_on ideas

that were popular at the time, but creating a unique combination of designs.

      The nineteenthcentury poor city was in many ways a terrible place, dirty and crowded; but it offered

economic and social opportunities.At the same time, the British countryside was in fact equally unattractive: though it promised fresh air and nature, it suffered from agricultural depression(萧条) and it offered neither enough work and wages, nor much social life.Howard's idea was to combine the best of town and country in a new kind of settlement,the garden city.Howard's idea was that a group of people should set up a

company, borrowing money to establish a garden city in the depressed countryside, far enough from

existing cities to make sure that the land was bought at the bottom price.

     Garden cities would provide a central public open space, radial avenues and connecting industries.

They would be surrounded by a much larger area of green belt, also owned by the company, containing

not merely farms but also some industrial institutions.As more and more people moved in, the garden city would reach its planned limit-Howard suggested 32,000 people; then, another would be started a short

distance away.Thus, over time, there would develop a vast planned house collection, extending almost

without limit; within it, each garden city would offer a wide range of jobs and services, but each would

also be connected to the others by a rapid transportation system,thus giving all the economic and social

opportunities of a big city.

1. How did Howard get the name for his building plan of garden cities?

A. Through his observation of the country life.

B. Through the combination of different ideas.

C. By taking other people's advice.

D. By using the nickname of the reconstructed Chicago.

2. The underlined phrase "drawing on" in Paragraph 1 probably means________.

A. making use of  

B. making comments on

C. giving an explanation of  

D. giving a description of

3. According to Howard, garden cities should be built______.

A. as far as possible from existing cities

B. in the countryside where the land was cheap

C. in the countryside where agriculture was developed

D. near cities where employment opportunities already existed

4. What can we learn about garden cities from the last paragraph?

A. Their number would continue to rise.

B. Each one would continue to become larger.

C. People would live and work in the same place.

D. Each one would contain a certain type of business.

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