问题 问答题 论述题

电气设备中的铜铝接头,为什么不直接连接?

答案

参考答案:

如把铜和铝用简单的机械方法连接在一起,特别是在潮湿并含盐分的环境中(空气中总含有一定水分和少量的可溶性无机盐类),铜、铝这对接头就相当于浸泡在电解液内的一对电极,便会形成电位差(相当于1.68V原电池)。在原电池作用下,铝会很快地丧失电子而被腐蚀掉,从而使电气接头慢慢松弛,造成接触电阻增大。当流过电流时,接头发热,温度升高还会引起铝本身的塑性变形,更使接头部分的接触电阻增大。如此恶性循环,直到接头烧毁为止。因此,电气设备的铜、铝接头应采用经闪光焊接在一起的“铜铝过渡接头”后再分别连接。

阅读理解

阅读理解。

     Like most teenagers in the world, Joso Montanaro a teen artist in Brazil, likes reading and drawing

cartoons. But he is special-his drawings get published (出版).

     Montanaro is now drawing cartoons for Folha. Folha is Brazil's largest newspaper and is known for its

cartoons.

     Montanaro has already been working at Folha for two years. Each week he draws two, there or four

cartoons and sends them to the paper. From those editors choose one for the next day's page. Montanaro

draws about the news of the day. Recently he worked on The Wave-a drawing of the tsunami (海啸) that hit

Japan. Montanaro also likes to draw cartoons about the funny things that happen in Brazilian politics (政治).

     "I like doing political drawings because you can joke about somebody bigger than you." Montanaro says.

     Folha's art director, Mario Kanno, says editors saw something new and different in Montanaro's work."We

brought him in with this idea to show that, yes, young people also read newspapers and can show their ideas

on politics,"Kanno says.

     Montanaro's love for cartoons began when be was only 7 or 8 year old. His dad bought him comics.

Montanaro says these books gave him the ideas that got him drawing. "I think those great works have really

helped me," he says."They remind me that I should draw something in my book every day."

1. What is Montanaro doing for Folha now?

A. He is publishing story books.

B. He is drawing cartoons.

C. He is sending newspapers.

D. He is writing articles.

2. Which of the following is NOT true according to the passage?

A. Folha is famous for its cartoons.

B. Folha is the largest newspaper in Brazil.

C. Montanaro draws one cartoon for Folha every week.

D. Montanaro began to work for Folha two years ago.

3. Why does Montanaro like drawing political cartoons?

A. Because he can show his ideas on politics.

B. Because he is very interested in political jobs.

C. Because he thinks it's easier to draw political cartoons.

D. Because he can make fun of some important people.

4. What made Montanaro draw and helped him a lot in his drawings?

A. The comics his dad bought him.

B. His interest in cartoon films.

C. The fun of drawing cartoons.

D. His dad's ideas about cartoons.

5. What's the best title for this passage?

A. Folha's art director.

B. Brazil's largest newspaper.

C. Teen artist in Brazil.

D. Montanaro's great father.

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