问题 问答题

如图a为一个电灯两端电压与通过它的电流的变化关系曲线.由图可知,两者不成线性关系,这是由于焦耳热使灯丝的温度发生了变化的缘故,参考这条曲线回答下列问题(不计电流表和电池的内阻).

(1)若把三个这样的电灯串联后,接到电动势为12V的电源上,求流过灯泡的电流和每个灯泡的电阻;

(2)如图b所示,将两个这样的灯泡并联后再与10Ω的定值电阻串联,接在电动势为8V的电源上,求通过电流表的电流值以及每个灯的实际功率.

答案

(1)把三个这样的电灯串联后,每只灯泡的实际电压为

12
3
V=4V,再在图甲上可以查到每只电灯加上4V实际电压时的工作电流为I=0.4A,则此时每只电灯的实际电阻R=
U
I
=
4
0.4
Ω=10Ω.

(2)在题乙图中的混联电路中,设每只电灯加上的实际电压和实际电流分别为U和I.在这个闭合电路中,有

E=U+2IR0

代入数据并整理得,U=8-20I

这是一个直线方程,把该直线在题甲图上画出,如图所示.

这两条曲线的交点为U=2V、I=0.3A,同时满足了电路结构和元件的要求,此时通过电流表的电流值IA=2I=0.6A.

每只灯泡的实际功率P=UI=2×0.3=0.6W

答:

(1)若把三个这样的电灯串联后,接到电动势为12V的电源上,流过灯泡的电流为0.4A,每个灯泡的电阻为10Ω;

(2)如图乙所示,将两个这样的灯泡并联后再与10Ω的定值电阻串联,接在电动势为8V的电源上,通过电流表的电流值是0.3A,每个灯的实际功率为0.6W.

阅读理解

阅读理解

       BEIJING, June 11(Xinhua)一The Red Cross Society of China(RCSC)is planning to spend 2. 5 billion yuan (362. 32 million U. S. dollars)on reconstruction projects(重建工程)in areas hit by the May 12

earthquake.   

       The money would be the first part to go to reconstruction in quake areas from the donations the

RCSC had received so far, the organization said in a statement(声明)here on Wednesday. About 1. 8

billion yuan would go to the worst hit southwestern Sichuan Province, 460 million yuan to northwestern

Gansu Province and 240 million to Shaanxi Province.

       The funds would be spent in building hospitals,schools,houses and quake prevention facilities

(防震设施).

       The RCSC would first think of lonely areas and people in need,including orphans(孤儿), the

disabled and elderly who lost family members,the statement said.

       So far,the RCSC had received 4. 12 billion yuan of donations and 900 million yuan had been spent

in helping people hit by the earthquake.

       The rest of the donations would go to reconstruction projects,the statement said.

1. How much donation has the RCSC received so far?

A. 2. 5 billion yuan      

B. 240 million yuan

C. 4. 12 billion yuan    

D. 900 million yuan

2. For the reconstruction projects,how much would go to Sichuan Province?

A. 1. 8 billion yuan      

B. 460 million yuan

C. 240 million yuan      

D. 2. 5 billion yuan

3. Which province was the most seriously hit the May 12 earthquake?       

A. Gansu    

B. Jiangsu    

C. Sichuan  

D. Shaanxi

4. The money would first be spent to help_______.

A. orphans,homeless people and the disabled

B. any people in need

C. children and the elderly

D. we don't know  

单项选择题