题干

在如图所示的电路中,定值电阻R2阻值为10欧,电源电压为3伏且保持不变,当电键S闭合后,干路中的电流为1安,求:

①通过电阻R2的电流;

②电路消耗的总电功率.

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答案(点此获取答案解析)

解:由电路图可知,当电键S闭合后,两电阻并联,电流表A测R2支路的电流.

①因并联电路中各支路两端的电压相等,

所以,通过电阻R2的电流:

I2= =

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I liked buying clothes, so I had a lot of clothes! One day, I looked at my closet(衣橱) and it   26   me. Pictures of homeless kids came into my mind. I thought of them begging(乞讨) on the streets with pretty old   27  , so I decided to do something for them. 

I took several bags and   28   them with clothes, leaving my closet half full.  

It was in the afternoon. I saw some   29   kids on the street. They were like   30   without a shepherd(牧羊人). My heart   31  .

I handed two big boys the   32  , and they asked, “What are these?”

I said, “They are all yours. You share these with your family. Okay?” 

They didn’t   33   for a few minutes, but when they did, my   34   was full of a different feeling, like two big arms hugged(拥抱) my heart.

“Thank you. We will also   35   these with them!” they looked at the other kids on the street and said.  

I was very moved by the experience, and I hope everyone would love to clear their closets for homeless children. 

26A. worried                B. surprised                  C. liked                

27 A. toys                     B. friends                         C. clothes             

28 A. covered               B. carried                         C. filled               

29A. small                    B. homeless                  C. different           

30 A. girls                    B. boys                        C. sheep

31 A. beat                     B. jumped                    C. broke               

32 A. bags                    B. pictures                    C. hopes        

33 A. speak                   B. see                           C. cry                  

34 A. hand                    B. life                          C. heart

35 A. have                    B. take                         C. share