问题 问答题 简答题

试电笔有哪些用途?

答案

参考答案:

试电笔除能测量物体是否带电以外,还有以下几个用途:

(1)可以测量线路中任何导线之间是否同相或异相。(其方法是:站在一个与大地绝缘的物体上,两手各持一支试电笔,然后在待测的两根导线上进行测试,如果两支试电笔发光很亮,则这两要导线是异相,否则即同相)。

(2)可以辨别交流电和直流电。(在测试时如果电笔氖管中的两个极(管的两端)都发光,则是交流电。如果两个极只有一个极发光,则是直流电)。

(3)可判断直流电的正负极(接在直流电路上测试氖管发亮的一极是负极,不发亮的一极是正极)

(4)能判断直流是否接地。(在对地绝缘的直流系统中,可站在地上用试电笔接触直流系统中的正极或负极,如果试电笔氖管不亮,则没有接地现象,如果发亮,则说明接地存在,其发亮如在笔尖一端,则说明正极接地,如发亮在手指一端,则是负极接地)。

单项选择题
阅读理解

阅读理解。

     Buster Brown was a thief-and a good one,too,he thought.  He'd never been caught by the police

because he never took chances. He was always Prepared for any unforeseen event or emergency.

     Confidently,he stood outside the house Of his intended victim (受害者) and read the sign On the

front gate of the house. "Don't worry about the dog-be aware of the owner!"  it said. Buster smiled

and found his way in.

     The house looked quite normal outside,but inside it was very exotic with fascinating objects on

display. As he began putting them into his bag,a dog came into the room. It stopped when it saw

Buster, then wagged its tail madly and went over to. him,licking his outstretched hand. "Good boy,"

Buater whispered. "What a great guard dog you are-trying to lick me to death."

     Satisfied he'd made friends with the dog,Bluster began to wander round the house,choosing items

to put in his bag. His skilled eye picked out only the best antiques (古董): a pair of silver candleholders,

a silver tea-and-coffee service,etc.. His new friend,the dog,sat and watched, as if wondering what was

happening.

     "Well, boy," Buster whispered,finally. "That might do. Any more and I won't be able to carry it!" He

swung the heavy bag onto his shoulders, just as the lights came on, nearly blinding him. He shielded his

eyes with his hand.

     "You're a very silly person," the figure in the doorway said, his voice dry em dust. As the man came

closer, Buster could see he was well dressed. His face seemed familiar, but Buster couldn't quite place

where he had seen him before.

     "You should have taken more notice of the sign outside," the man rasped." I knew about this

attempted robbery last week and I also know you will end up behind bars for 20 years. Fancy trying to

rob the house of the world's greatest fortune-teller!"

1. Why was Buster so confident?

A. He was not afraid of dogs.

B. He knew the owner of the house lived alone.

C. He had never been caught by the police.

D. The house had no security alarm.

2. Which of the definitions is closest in meeting to the word "exotic" in the third paragraph?

A. Messy and untidy.

B. Rich and expensive.

C. Comfortable and calming.

D. Foreign and unusual.

3. How did Buster decide which objects to take?

A. He took those that were easy to carry in his bag.

B. He took only the best antiques.

C. He took those that he knew he could sell easily.

D. He looked for silver objects.

4. What punishment waits for Buster Brown?

A. A prison sentence with hard labour.

B. A long prison sentence.

C. A heavy fine.

D. Community service for 20 years.