问题 填空题

一用电器的电阻是20Ω,通过该电阻的电流是0.3A,用电压表测量该电阻两端的电压,则电压表的量程应选______;当通过该用电器的电流增加一倍,则用电器的电阻为______Ω,两端的电压为______v.

答案

(1)导体两端的电压U=IR=0.3A×20Ω=6V,电压表应选0~15V量程;

(2)通过该用电器的电流增加一倍时,导体的材料、长度、横截面积不变,导体的电阻不变,电阻为20Ω;

(3)通过用电器的电流增加一倍时,流过用电器的电流I′=2I=2×0.3A=0.6A,两端电压U=I′R=0.6A×20Ω=12V;

故答案为:0~15V;20;12.

选择题
阅读理解

As De Witt Wallace lay in bed recovering from injuries that he unfortunately came by in World War I, he found there was a wealth of interesting information to read. Realizing few people would have the time to get through all this information, he knew exactly what to do. In 1920, this young American submitted a sample magazine containing shortened articles to publishers across America. However, all turned him down.

Undeterred, De Witt and his new bride Lila Bell Acheson published the first issue of Reader’s Digest in February 1922. Working from home, the Wallaces printed 5,000 copies, which were sold by mail to 1,500 people and priced at 25 cents. From these humble beginnings grew the world’s most widely–read magazine.

The magazine became popular and, by 1935, sales topped one million. In 1938, the first international edition was published in the United Kingdom. During World War Ⅱ, editions were published for the first time in Latin America and Sweden. After the war Reader’s Digest moved into Australia, Belgium, Canada, Denmark, Finland, France, Germany, Italy, Norway, South Africa and Switzerland. In 1950, Reader’s Digest published its shortened Books (now known as Select Editions in Australia). In 1959, music, the first non–print product line, was introduced. In 1962, Reader’s Digest revolutionized direct mail by introducing easy–to–enter Sweepstakes and a year later the first Reader’s Digest general book was published. In 1986, video was added to the Reader’s Digest product line.

In 1973, the Wallaces gave up active management of Reader’s Digest. De Witt died in 1981, aged 91; Lila in 1984, aged 94. With no heirs(继承人) to the Wallace empire to take control, Reader’s Digest became a public company in the early 1990s and is now headed by a Chief Executive Office and Chairman of the Board.

小题1:What is the purpose of De Witt Wallace creating the earliest magazine?

A.To become wealthy.

B.To offer people information.

C.To heal the wounds from the war.

D.To turn down uninteresting stories.小题2:When did De Will make his first trial of the magazine?

A.Before World War I.

B.In 1920.

C.In 1922.

D.In 1935.小题3:What is mainly talked about in the first two paragraphs?

A.The first issue of Reader’s Digest.

B.The first trial of De Witt Wallace’s dream.

C.De Witt Wallace’s character and marriage.

D.The humble beginnings of Reader’s Digest.小题4:Which of the following is the right order for the history of Reader’s Digest?

a.The Select Edition came out.

b.The Wallaces retired from the management of Reader’s Digest.

c.The magazine sold over million copies.

d.The product line was improved by means of videos.

e.Editions in other languages were published.

A.c — e — a — b — d

B.e — a — c — b — d

C.c — e — a — d — b

D.a — c — e — d — b小题5:What can be known about Reader’s Digest from the passage?

A.Reader’s Digest only published shortened or general books.

B.After World War ⅡReader’s Digest was published all over the world.

C.Reader’s Digest was first private–owned and later public–owned.

D.Reader’s Digest has always been headed by a Chief Executive Office