问题 计算题

在图中,R1=5Ω,R2=10Ω,当开关S闭合时,电流表的示数为0.6A。

求(1)电源电压;

(2)R1支路的电流。

答案

6V;1.2A

题目分析:由电路分析可知,两电阻并联,电流表A与R2串联,故A测量R2的电流,

根据题意,已知R2的电阻和通过R2的电流,所以即可求出R2的两端电压,根据并联电路电压特点,各支路电压均相等,所以可知R1支路的电压,再根据欧姆定律,即可求出通过R1支路的电流。

(1)由题意可知,通过R2的电流

根据欧姆定律I=可得

电源电压U=I2R2=0.6A×10Ω=6V

(2)通过R1支路的电流

点评:本题为一综合题,均为简单应用,故难度不大.

单项选择题
阅读理解

Reading comprehension

     Last week I visited one of my old neighborhoods in Washington D.C. I had not been there for twenty

years and as I walked along the street, my mind was flooded by memories of the past. I saw the old

apartment building where I had lived and the playground where I had played. As I viewed these once

familiar surroundings, images of myself as a child there came to mind. However, what I saw and what I

remembered were not the same. I sadly realized that the best memories are those left untouched.

     My old apartment building, as I remember, was bright and alive. It was more than just a place to live.

It was a movie house, a space station, or whatever my young mind could imagine. I would steal away

with my friends and play in the basement. This was always exciting because it was so cool and dark, and

there were so many things there to hide among. There was a small river in the back of the building. We

would go there to lie in the shade of trees and enjoy ourselves.

     However, what I saw was completely different. The apartment building was now in disrepair. What

was once more than a place to live looked hardly worth living in. The windows were all broken. The

once clean walls were covered with dirty marks. The river was hardly recognizable. The water was

polluted and the trees and flowers were all dead. The once sweet-smelling river now smelled terrible. It

was really heartbreaking to see all this.

     I do not regret having seen my old neighborhood. However, I do not think my innocent childhood

memories can ever be the same. I suppose it is true when they say, "You can never go home again."

1. In the first two paragraphs of the passage the writer tries to tell us that ________.

A. he had lived in Washington D.C. for twenty years

B. he was very imaginative when he was a child

C. he had had pleasant memories of his old neighborhood

D. he had come from a very poor neighborhood

2. How did the writer feel when he visited his old neighborhood in Washington D.C.?

A. Greatly surprised.

B. Very regretful.

C. Quite excited.

D. Very sad.

3. On his visit to his hometown, the writer found the old apartment building ________.

A. seemed unfit to live in

B. had been repaired

C. could hardly be recognized

D. looked dirty and smelt horrible

4. "You can never go home again" in the last sentence of this passage means that ________.

A. one should never revisit his hometown after many years of absence

B. one will never find his hometown the same as it was in his childhood memory

C. a visit to one's hometown will bring back one's pleasant memories of home

D. a visit to one's hometown will bring back many sad memories