问题 问答题

人是被电“吸“住了吗?

常听人们有这种说法:触电时人被电吸住了,抽不开.

实际上这个说法是错误的.人手触电时,由于电流的刺激,手会由痉挛到麻痹.即使发出抽回手的指令,无奈手已无法执行这一指令了.调查表明,绝大多数触电死亡者,都是手的掌心或手指与掌心的同侧部位触电.刚触电时,手因条件反射而弯曲,而弯曲的方向恰使手不自觉地握住了导线. 这样,加长了触电时间,手很快地痉挛以致麻痹. 这时即使想到应松开手指、抽回手臂,已不可能,形似被“吸住“了.如若触电时间再长一点,人的中枢神经都已麻痹,此时更不会抽手了. 这些过程都是在较短的时间内发生的.

如手的背面触电,对一般的民用电,则不容易导致死亡,有经验的电工为了判断用电器是否漏电而手边又无线电笔,有时就用食指指甲一面去轻触用电器外壳. 若漏电,则食指将因条件反向而弯曲,弯曲的方向又恰是脱离用电器的方向. 这样,触电时间很短,不致有危险.当然,电压很高,这样作也会发生危险,所以,一定要注意用电安全.

①家庭电路中,输电线进户后,在接用电器之前,还要经过一些装置,这些装置的顺序是( ______)

A.电能表、保险盒、总开关            B.电能表、总开关、保险盒

C.总开关、电能表、保险盒            D.总开关、保险盒、电能表

②下列能引起触电事故的是 ( ______)

A、两手同时接触一节干电池的两极

B、人站在干燥的木凳上,一只手单接触火线

C、人站在地面上,双手同时分别接触家庭电路中的火线和零线

D、人站在地面上,双手同时接触家庭电路中的零线

③关于安全用电,你能说出几条建议吗?

答案

(1)进户线首先进入电能表,这样防止一些人私自拆接电能表;总开关接在电能表的后面,能使整个家庭电路在检修时断开总开关,而不影响其他用户;保险丝要接在总开关的后面,当保险丝熔断后更换保险丝时更安全;后面再接入家用电器.

(2)A、一节干电池的电压是1.5V,小于人体的安全电压,不会对人体造成危害.不符合题意.

B、人站在干木凳上,接触火线,在人体上不能形成通路,不会对人体造成危害.不符合题意.

C、人站在地面上,双手同时分别接触家庭电路中的火线和零线,火线和零线之间的电压是220V,加在人体的电压是220V,超过人体的安全电压,会对人体造成危害.符合题意.

D、人站在地面上,双手同时接触家庭电路中的零线,大地和零线之间的电压是0V,不会对人体造成危害.不符合题意.

(3)不要用湿手摸插头;不要在电线上晾衣服;电视天线远离电线;金属外壳的用电器一定使用三孔插座;不靠近断开的高压线;有人触电时不要用手直接拉,首先切断电源.

故答案为:①B;②C;③不要用湿手摸插头;不要在电线上晾衣服;电视天线远离电线;金属外壳的用电器一定使用三孔插座.(答案不唯一)

阅读理解

阅读理解。

     Very few people enjoy exams. I don't, either. And although I tell myself not to worry about them, I always

do! So I am not surprised that my students worry about them, too, even though they usually don't need to.

Because they are afraid of failing. However, since it is hard not to worry at all, we all must try not to worry

too much. Why? Because worrying makes exams worse! How to do this?

     1. Ask the teacher about how to revise and about exam skills- how to work when you are in the exam.

     2. Good students don't wait until the week before an exam. They study all through the year. It is not

possible to learn everything at the last minute. So don't leave it till then!

    3. If you start planning and working for each exam early and you make sure that you understand what

you are studying, then, when it is over, you'll be able to say, "What a good exam that was!"

     4. Take a short rest during your time of work and revision. If your mind is tired, it will not remember well.

Work at the time when you know you will work at your best.

     5. If you are studying in the evening, don't go straight to bed afterwards. Your mind will still be "going

round and round" - thinking too much. Do something else, maybe walk or get exercise. Choose something

that will relax you, and make you think of other things.

    6. If you feel bad, talk to someone about your worries. But don't be too relaxed! Some stress over exams

makes you work hard for them.

1. How does the writer feel about exams?

A. Excited.

B. Bored.

C. Worried.

D. Surprised.

2. Why are the students afraid of exams?

A. Because they are afraid of failing.

B. Because they want to get full marks.

C. Because exams are usually hard.

D. Because they think their teachers will be angry with them they can't pass the exams.

3. Which is NOT mentioned (提到) in the passage?

A. Good students don't wait until the week before an exam.

B. Start planning and working for each exam early.

C. If you don't know how to work for an exam,ask the teach about it.

D. You should sleep well before the exam.

4. According to the passage, if you feel bad, you'd better ______.

A. take a short rest

B. tell someone about your worries

C. walk or get exercise

D. keep busy working and forget your worries

5. The writer of the passage is probably a ______.

A. student

B. teacher

C. journalist

D. scientist

选择题