问题 计算题

有一个灯泡,它的电阻是10Ω,把灯泡两端加6V电压时,灯泡能正常工作.如果把灯泡接在9V的电源上,仍使灯泡正常发光,应给灯泡串联一个多大的电阻?

答案

解:灯泡正常发光时的电压为UL=6V

当把灯泡接在9V的电源上,仍使灯泡正常发光时

则:=,即=

所以R=5Ω

阅读理解

阅读短文,选择正确答案。

       Mike lives in a small town. He works in the zoo and loves the animals very much. And he has a dog, he

always plays with it, he often saves (节约) money to buy some nice food for it.

       One day a friend of his asks him to dinner. He goes there with his dog. When they are eating, he throws

some meat, fish, chicken and cakes to it. 

       His friend asks, "You love your dog very much, don't you?" "Yes," Mike says. "And it is very clever. If you

give it some money, it can buy some newspapers for you." So his friend gives the dog some money and it goes

out at once.

       An hour later the dog doesn't come back. Mike looks worried and asks, "How much do you give my dog?"

"Ten dollars," answers his friend. "You give it too much," says Mike. "I think it must go to a movie now."

1. Mike often buys some nice food for _______. [ ]

A. the animals

B. his dog

C. his friend

D. himself

2. For dinner Mike throws some ______ to his dog. [ ]

A. food

B. fruit

C. money

D. newspapers

3. The dog is very clever because ______. [ ]

A. it always plays with Mike

B. it knows how to save money

C. it can buy some newspapers for people

D. it can read newspapers

4. The dog doesn't come back because ______. [ ]

A. it is in the zoo

B. it goes to a movie

C. it is lost (失踪,迷路)

D. it buys the newspapers

5. Which of the following is NOT right? [ ]

A. Mike likes the animals very much.

B. The dog can help Mike do something.

C. Mike's friend gives the dog ten dollars.

D. Mike's friend wants to go to a movie.

实验题