问题 问答题 论述题

用电流表测量电路中电流时,不慎将电流表与负载(负载电阻很大)并联,会产生什么后果?

答案

参考答案:

电流表的内阻是很小的,如果误将电流表与负载并联,电路的等效负载电阻应是电流表内阻与负载电阻并联。由于电流表内阻小,并联后的等效电阻数值很小,使回路中电流增大,远远大于负载的正常电流此电流几乎全部从电流表上流过,完全可能超过电流表最大量程许多倍,造成电流表损坏。另外,由于电路中电流很大,电源设备也可能因超负荷而出现故障。

阅读理解

阅读理解。

    One afternoon, Henry, an old man from America, telephoned from the airport to tell me that he had arrived.

He was going to stay with me. I was still at the office at the time, but I had prepared for his coming. After

explaining where my new house was, I told him where I had left the key. As I was likely to be home rather late,

I asked him to go into the kitchen and help himself to food and drink.

    Two hours later my friend telephoned me from the flat. At the moment, he said, he was listening to some of

my records after having just had a truly wonderful meal. He had cooked two eggs and had helped himself to

some cold chicken from the refrigerator.

     Now, he said, he was drinking a glass of orange juice and he hoped I would join him. When I asked him if

he had reached the flat without difficulty he answered that he had not been able to find the key, but luckily the

living-room window just by the apple tree had been left open and he had climbed in. I listened to all this in

surprise. There is no apple tree in front of my living-room, but there is one in front of my neighbour's!

1. I knew that Henry would _____. [ ]

A. call at my office

B. arrive

C. telephone me from the airport

D. meet my neighbour

2. I asked him to go into the kitchen and help himself to food and drink because _____. [ ]

A. he was very hungry

B. he liked good food

C. I would very probably be home late

D. I disliked being bothered

3. Henry said he was listening to some of the records _____. [ ]

A. before he had a meal

B. because he had nothing to do

C. because he wasn' t hungry

D. after he had had a wonderful meal

4. When Henry telephoned me from the flat he was _____. [ ]

A. listening to some records

B. drinking a glass of orange juice

C. doing nothing

D. both A and B

5. Henry entered the house _____. [ ]

A. without difficulty

B. as he had been told to

C. through the open window

D. by opening the door with the key

判断题