问题 选择题

下列关于电场线的说法中,正确的是(  )

A.电场线是电场中真实存在的线

B.电场线上任何一点的切线方向总是与置于该点的点电荷的受力方向一致

C.电场中各点的电场强度的大小总是沿着电场线方向减小

D.电场线是从正电荷出发到负电荷终止的曲线

答案

A、电场线是形象地描述电场而假想的曲线,是不存在的.故A错误;

B、电场线的方向是正电荷所受电场力的方向,与负电荷所受电场力的方向相反,故B错误;

C、电场线的疏密代表电场的强弱,故电场线越密的地方场强越强,电场强度大小与电场线方向无关,故C错误;

D、电场线始于正电荷(或无穷远)止于负电荷(或无穷远),故D正确.

故选D.

完形填空

短文填空 阅读下则短文,然后在空白处写出适当的单词,单词首字母已给出。[有的词请注意词形的变化!] (共12个空,做对一个得1分,共10分)

How times flies! Junior 3 students will take the senior high school student entrance exam. They are studying hard for this big challenge, and they are also 小题1:w     about it. Do they have time to do something to celebrate their middle school years? Many do.

Liu Jia, 14, from Beijing said that in her class students are 小题2:w     goodbye messages or letters for each other. They are also giving photos to each other.

“Even the head teacher has a project,” said Liu. “She 小题3:p     to put all our class photos onto a CD and give each student one.”

Li Wei, 14, in Xianning, Hubei said that their English teacher Ms Deng asks them to write what they want to be when they小题4:g     up on the paper. She likes her students to come back after they graduate, and share their teen-time dreams together. Doing that 小题5:e     her students to work harder for their future.

Chen Ze, 15, in Guangzhou said his classmates are making “lucky stars” as graduation 小题6:g     . The cheerful stars are 小题7:m     of colored paper.

“小题8:B     you make a lucky star, you write some words for the person on the paper,” said Chen. “He or she can read the words after they open the star.”

In Xiao Xing’s school, each Junior 3 student will get a yearbook, in which the graduation classes will put their photos and self-introductions(自我介绍).

Xiao said, “ We have written a 小题9:p     in the ancient style as the self-introduction!”

“Our class may be not the one with the best school grade but it must be the 小题10:m    creative one,” said Xiao. “ I feel 小题11:p     of studying in such a class!”

What good ideas! I think all those will 小题12:r     them of their good days.

名词解释