问题 问答题 简答题

什么是晶体压电效应?请举例说明。

答案

参考答案:

当某些晶体沿一定方向伸长或压缩时,在其表面上会产生电荷,这种效应称为压电效应。一些晶体当不受外力作用时,晶体的正负电荷中心相重合,单位体积中的电距等于零,晶体对外不呈现极性,而在外力作用下晶体形变时,正负电荷的中心发生分离,这是单位体积的电锯不再等于零,晶体表现出极性。另外一些晶体由于具有中心对称的结构,无论外力如何作用,晶体正负电荷的中心总是重合在一起,因此这些晶体不会出现压电效应。

阅读理解

阅读理解。

     On a Friday night, a poor young violinist was playing his violin at the entrance of the sub-way station.

The music was so great that people slowed down to listen and put some money into his hat.

     The next day, the violinist came to the entrance again. He put down his hat as usual. Be-side the hat

was a piece of paper with some words on it. It said, A George Sang has put an important thing into my

hat by mistake.

     "Welcome to claim it." Soon the people were attracted by the words and wondered what it could be.

After a while a man rushed through the crowd, took it! violinist's shoulders and said, "I knew you would

certainly come here." The violinist asked, "Did you lose something?" "Lottery." The violinist took out

lottery ticket with Sang's name on it. Sang took it and danced happily.

     Sang was an office worker. He bought the lottery and won a prize of $500,000. But when he gave $50

to the violinist for his wonderful music, the lottery ticket was thrown in, too. The violinist was a college

student. This morning, he was going to fly to Vienna for high education. However, when he found the

ticket, he cancelled the flight and returned to the entrance.

     Later someone asked the violinist why he didn't take the lottery ticket to pay the tuition fee. He said,

"Although I don't have much money, I live happily. If lose honesty, I won't be happy forever."

1. Why did the young man play the violin at the entrance?

A. For pleasure.

B. To earn money.

C. For love.

2. What did George Sang put into the violinist's hat on a Friday night by mistake?

A. Money.

B. Lottery.

C. Money and lottery.

3. George Sang was very _____ to see the young violinist the next day.

A. worried

B. sorry

C. happy

4. What does the underlined word "cancelled" in the fourth paragraph mean?

A. 增加

B. 取消

C. 上升

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

A. The Meaning of Honesty.

B. An Office Worker and a Lottery Ticket.

C. The Wonderful Violin Play.

单项选择题