问题 计算题

如图所示的电路中,电源电压不变,电阻R1=20Ω。当开关S接位置1时,电流表的示数为0.6A;当开关S接位置2时,电流表的示数为0.2A。求:

(1)电源电压。

(2)开关S接位置2时,电阻R2消耗的电功率。

答案

解:

(1)U=I1R1=0.6A×20Ω=12V;

(2)当开关接位置2时, U1=I1R1=0.2A×20Ω=4V

U2=U-U1=12V-4V=8V

P2 =I2U2=0.2A×8V=1.6W。

阅读理解

Dear Abby,

I'm a helpless mother. My son Tom is 15 years old. I find that the older he grows, the less we talk. I feel very sad and I really need help.

My first problem is about his hobbies. He spends almost all his spare time on computer games. When he gets home, he always turns on the computer and closes the door. I'm getting worried about him, especially when his English teacher tells me he always gets low marks in the English exams.

Second, he likes new technology, but I don't have enough money and I can't afford all the things he wants.

Recently, I've found that he is always alone. I've never seen him talking to his friends on the phone or going out with anyone on weekends. That is the last problem I have.

What should I do to help him? Please give me some advice.

A helpless mother

小题1:The helpless mother has         problems.

A.two

B.three

C.four

D.five小题2:Tom           for almost all his spare time at home.

A.plays computer games

B.talks with his mother

C.does his homework

D.practises typing (打字)小题3:From the passage we know that Tom's mother           .

A.is not worried about Tom

B.feels very happy

C.is not rich

D.likes new technology小题4:The helpless mother asks Abby to             

A.play with Tom

B.talk to Tom

C.buy what Tom wants

D.give her some advice小题5:Which of the following is TRUE about Tom?

A.He is 14 years old.

B.He is not good at English.

C.He often phones to his friends.

D.He likes going out on weekends.

问答题