问题 问答题

定值电阻R1和R2并联后,接在电压可调的电源两端,电路中的干路电流I随电源电压U变化关系的图象如图所示.已知R1=20Ω,则R2=______Ω.

答案

由图象可知,当电源的电压U=6V时,干路电流I=0.5A,

根据欧姆定律可得,并联电路的总电阻:

R=

U
I
=
6v
0.5A
=12Ω,

∵并联电路中总电阻的倒数等于各分电阻的倒数之和,

1
R
=
1
R1
+
1
R2
,即
1
12Ω
=
1
20Ω
+
1
R2

解得:R2=30Ω.

故答案为:30.

阅读理解

阅读理解

     At this moment in different places of the world people are doing different things.

     In Beijing it's early morning. People are sleeping.

     In London people are leaving work to go home. They are waiting for buses or trains. Some people

are driving their cars. Some are having afternoon tea at home or walking to the pubs(酒吧) to have a

drink.

     In Moscow it's evening and people are having supper at home or in restaurants.

     Some are going to watch a ballet(芭蕾舞). Some are drinking in the pubs.

     In Los Angeles(洛杉矾) it's morning. People are working in their offices. Children are starting their

lessons.

     New York is noon now. People aren't working but having lunch. They are eating hamburgers or hot

dogs and drinking coffee or Coke. Some people are seeing friends or shopping.

1. According to the passage we can see that at night some people in Moscow like to __________.

A. go to watch a ballet

B. do shopping

C. wait for buses

D. go to the library

2. When children in Los Angeles are starting their lesson, people in Beijing are __________.

A. playing basketball

B. seeing films

C. having lessons

D. sleeping

3. From the passage, we can see the time in New York now is __________.

A. 6:00

B. 9:00

C. 10:00

D. 12:00

4. We know that London is 3 hours __________.

A. earlier than Moscow

B. later than Moscow

C. earlier than Los Angeles

D. later than Los Angeles

5. This passage mainly talks about __________.

A. science

B. holiday

C. time difference(区别)

D. life in western countries

单项选择题