问题 计算题

(14分)如图所示,匀强电场中有a、b、c三点,ab=5cm,bc=12cm,其中ab沿电场方向,bc和电场方向成60º角,一个电荷量为q=4×10─8C的正电荷从a移到b,电场力做功为W1=1.2×10─7J,求:

(1)匀强电场的场强E;

(2)电荷从b移到c,电场力做的功W2

(3)a、c两点的电势差Uac。

答案

(1)60V/m (2)1.44×10─7J   (3)6.6V

题目分析:(1)设ab间距为d1,则有:W1=qEd1

解得:=60V/m

设bc两点沿场强方向的距离为d2,则有:=1.44×10─7J。

(3)电荷从a移到c电场力做功为:W=W1+W2=qUac

所以:=6.6V。

阅读理解

Can you understand the beginning of this essay?

“My smmr hols wr CWOTT. B4, we usd 2go2 NY 2C my bro, his GF & 3 kds FTF.”

The Scottish teacher who received it in class had no idea what the girl who wrote it meant. The essay was written in a form of English used in cell phone text messages. Text messages (also called SMS2) through cell phones became very popular in the late 1990s. At first, mobile phone companies thought that text messaging would be a good way to send messages to customers, but customers quickly began to use the text messaging service to send messages to each other. Teenagers in particular enjoyed using text messaging, and they began to create a new language for messages called texting.

A text message is limited to 160 characters, including letters, spaces, and numbers, so messages must be kept short. In addition, typing on the small keypad of a cell phone is difficult, so it’s common to make words shorter. In texting, a single letter or number can represent a word, like “r” for “are,”“u” for “you,” and “2” for “to.” Several letters can also represent a phrase, like “lol” for “laughing out loud.” Another characteristic of texting is the leaving out of letters in a word, like spelling “please” as “pls.”

Some parents and teachers worry that texting will make children bad spellers and bad writers. The student who wrote the essay at the top of this page said writing that way was more comfortable for her. (The essay said, “My summer holidays were a complete waste of time. Before, we used to go to New York to see my brother, his girlfriend, and their three kids face to face.”)

Not everyone agrees that texting is a bad thing. Some experts say languages always evolve, and this is just another way for English to change. Other people believe texting will disappear soon. New technology for voice messages may soon make text messages a thing of the past.

小题1:What is the writer’s opinion of text messaging?

A.It is fun and easy to do.

B.It is not bad for children.

C.It will make children bad writers.

D.The writer does not give an opinion.小题2:Which characteristic of texting is NOT described in the passage?

A.Using phrases to represent essays

B.Using numbers to represent words

C.Using letters to represent phrases

D.Using letters to represent words小题3:Which of the following was most probably the title of the student’s essay?

A.My Gr8 Tchr

B.CU in LA

C.My GF

D.My Smmr Hols小题4:   Why do some people think that texting is bad?

A.It costs too much.

B.It’s too difficult to type.

C.Children won’t learn to write correctly.

D.It’s not comfortable.小题5:Why aren’t some people worried about the effect of texting?

A.Not many people use texting.

B.Spelling in English is too difficult.

C.Children quickly become bored with texting.

D.Texting will disappear because of new technology.

单项选择题