问题 选择题

下列关于电磁波的正确认识有(  )

A.在真空中电磁波的传播速度跟光速相等

B.赫兹预言了电磁波的存在,20多年后麦克斯韦用实验证实

C.电磁波和机械波都依靠介质来传播

D.只要空间某个区域存在电场和磁场,就能产生电磁波

答案

A、光就是一种电磁波,所以电磁波的传播速度与光速相同,故A正确;

B、麦克斯韦预言了电磁波的存在,20多年后赫兹用实验证实,故B错误;

C、电磁波是物质,故其传播不需要介质,而机械波的传播需要介质,故C错误;

D、电磁波是电磁场的一种运动形态.电与磁可说是一体两面,变化的电场会产生磁场(即电流会产生磁场),变化的磁场则会产生电场.变化的电场和变化的磁场构成了一个不可分离的统一的场,这就是电磁场,而变化的电磁场在空间的传播形成了电磁波,电磁的变动就如同微风轻拂水面产生水波一般,因此被称为电磁波,也常称为电波.故D错误;

故选A.

单项选择题
阅读理解

阅读理解。

     Nikkli was brought up from a vey early age by her father while her sister was raised by her mother.

Nikki spent a very small amount of time with her mum and sister when she was about 6 years old, but

soon after contact stopped when communication broke down between her parents.

     She never felt she wanted to find her family while she was growing up. But now with a husband and

a son, she decided it was the right time.

     Nikki didn't know where to start, but her husband's mum had used 192. com for finding people

before and recommended it to her. With the help of her son, she started by searching for her sister's

full name on the electoral roll (选民登记册) without a location, because she had no idea where she

lived, even her date of birth. From that one search, the site returned two results listed in the area they

used to live.

     Nikki decided to call the first number. To her absolute surprise, it was her long lost sister! So after

20 years, it was one phone call that helped her contact her sister! Her sister then passed her number

on to her mother, who called Nikki straight away, and it was like they had never been apart.

     Her mum was so glad to find out Nikki was well that they arranged to meet everyone that Saturday

(3 days after the phone call) where she was reunited with her sister and met her two nephews for the

first time. Nikki also found out she had a half (同父异母的) sister and brother.

     When talking about the reunion, Nikki said, "192.com made finding my long lost family very easy.

I was not on any social networking sites before and surprisingly neither was my sister or mum, so we

would never have found each other that way."

     Nikki will be spending her first Christmas tighter with the other side of her family this year.

1. What did Nikki know about her sister before her searching? 

A. Her address.  

B. Her birthday.  

C. Her name.  

D. Her telephone number.

2. It can be inferred from Paragraph 4 that _________.

A. Nikki's mum has a bad memory now

B. Nikki is about 26 years old now

C. Nikki's sister lives with her mum together

D. Nikki dialed another phone number to contact her mum

3. What can we learn about Nikki from the passage?

A. She knows much about the Internet.

B. Her sister has not got married so far.

C. Her mum got birth to four children in all.

D. She got in touch with her mum on Monday.

4. All of the following made contributions to Nikki's reunion with her family EXCEPT _______.  

A. her father    

B. 192.com      

C. her son      

D. her mother-in-law

5. The text is mainly about _______. 

A. how to find a family member

B. a wonderful Christmas

C. how important the electoral roll is

D. a family reunion thanks to 192.com