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问题 计算题

如图所示的电路中各元件值分别为：R1=R2=10Ω，R3=R4=20Ω，电容C= 300μF，电源电动势E=6V，内阻不计，原先双掷开关S与触点2接触，当开关S从与触点2接触改为与触点1接触，且电路稳定后，试求：

（1）电容器C所带电荷量；

（2）若开关从与触点1接触改为触点2接触，直到电流变为零时为止，求通过电阻R1的电荷量。

答案

解：（1）S与触点1接触时，回路电流

电容器两极间电压Uc=I（R2+R3）=3 V

电容器的带电荷量Q=CUc=9×10-4 C

（2）4.5×10-4 C

阅读理解

Many children think mobile phones are cool. They come in fun colors and let you talk with friends anytime and anywhere.

In the U.S., more than 90 million people use mobile phones. Many of these people are children. For children, mobile phones are more than phone calls. They are fashionable.

Most mobile phone users don’t think about the health problems caused(引起) by mobile phones. Some scientists say that mobile phones give off radiation(辐射) that might be bad for the users. One newest study shows that mobile phone radiation might raise(增加) a person’s chance of getting some kinds of cancer(癌症). Other scientists say mobile phones don’t’ threaten people’s health. They say that they have not found any link(联系) between phone use and cancer.

Scientists say that people can protect (保护) themselves from mobile phone radiation. One way is to use a headset(耳机). Or people can make shorter call.

小题1:Many children like mobile phones because they think mobile phones are _________.

A．cool

B．small

C．cheap

D．their toys小题2:Many of the mobile phone users in the U.S. are ___________.

A．girls

B．boys

C．scientists

D．children小题3:Some scientists think mobile phones aren’t _________ for users health. They causes some kinds of cancer

A．bad

B．good

C．wrong

D．helpful小题4:The underlined word “threaten” in the passage means ____________.

A．威胁.

B．担心

C．治疗

D．证实小题5:What should people do to protect themselves from mobile phone radiation?

A．Make longer calls

B．Use a headset

C．Make shorter calls

D．Both B and C
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单项选择题

文化的繁荣离不开文化人的______，从某种意义上说，文化人自身______的高低直接影响着文化产品的高下。
依次填入划横线部分最恰当的一项是( )。

A．付出 操守
B．支撑 品位
C．奉献 造诣
D．奋斗 修养
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