问题 实验题

某课外兴趣小组在做测定“小灯泡的电功率”实验时,所用器材有电压为6V的电源,额定电压为2.5V的小灯泡,以及符合实验要求的滑动变阻器、电表、开关和导线。如图a是没有连接完的实物电路。

(1)请你用笔画线代替导线,将实物电路连接完整;

(2)连好电路后,闭合开关,移动滑片P,发现小灯泡始终不亮,但电压表有示数,电流表无示数,则故障的原因可能是                           

(3)排除故障后闭合开关,移动滑片P到某处,电压表的示数为2.2V,要测量小灯泡的额定功率,应将滑片P向     端滑动(选填“左”或“右”),直到电压表的示数为     V,记录电流表的示数;

(4)通过移动滑片P,分别记下了多组对应的电压表和电流表的读数,并绘制成了如图b所示的U-I图像。根据U-I图像提供的信息,可计算出小灯泡的额定功率是        W。

答案

(1)图略 (2)小灯泡断路 (3)右  2.5 (4)0.5W 

(1)小灯泡的额定电压是2.5V,所以电压表选择0~3V量程即可,灯泡右端接线柱解电压表3V接线柱,电路图如图所示:

(2)移动变阻器滑片P,发现小灯泡始终不亮,但电压表有示数,电流表无示数,则故障的原因可能是小灯泡断路.

(3)电压表的示数为2.2V,小于额定电压,滑动变阻器滑片向右移动,使接入电路的电阻变小,电流变大,灯泡两端的电压变大,达到额定电压.

(4)由图象知U=2.5V时,I=0.2A,则小灯泡的额定功率P=UI=2.5V×0.2A=0.5W

阅读理解

阅读理解。

     A king gave his daughter a beautiful necklace. However , the necklace was stolen. So the kingtold

his people to look for it and said that he would give $ 50,000 to anyone who found it.

     One day, a man was walking along a dirty river. Suddenly , he saw the shining necklace in the river.

He decided to pick it up so that he could get the $ 50,000.

     He put his hand into the dirty river, but anyhow he couldn't get the necklace. He looked again and

the necklace was still there. He tried again. This time he walked into the river and put his whole arm in

to pick it up. But he still missed the necklace. Then again,he saw that the necklace was still right there.

So he became very angry.

     Just then, a boy saw him and asked him what was the matter. The man didn't tell the boy, thinking

that the boy might take the necklace for himself.

The boy could see that this man was in trouble. So he asked the man again and said that the would not

tell anyone about it. Thinking for a few minutes, the man decided to trust the boy. After telling the boy

what he was doing, the boy said, "Maybe you should try looking up into the tree."The man looked up

and saw that the necklace was shining in the tree.

1. What happened to the necklace?

A. It was broken.

B. It was stolen.

C. It was dirty.    

D. It was lent to the boy.

2. How did the man feel when he saw the necklace was still in the river after trying two times to get it?

A. He felt proud.

B. He felt happy.

C. He felt frightened.

D. He felt angry.

3. Why didn't the man tell the boy his trouble at first?

A. Because he didn't know the boy.

B. Because he haven't seen the boy before.

C. Because he thought the boy might take the necklace for himself.

D. Because the boy was the owner of the necklace.

4. Where did the man find the necklace at last?

A. In the dirty river.

B. In the tree.

C. In the boy's hand.

D. In the boy's house.

5. The writer wants to tell us that ______.

A. the necklace is very expensive

B. we shouldn 't put the necklace into the river

C. trusting others sometimes brings us good luck

D. we should never trust others because they can bring us bad luck

单项选择题