问题 实验题

如图甲所示为一个LED节能灯,它是用高亮度白色发光二极管做光源.某校科技活动组用以下方法来研究家用电灯和LED节能灯的发光效率:将额定功率均为15W的普通节能灯、白炽灯和LED节能灯依次接入同一照明电路,分别开灯10 min,让温度计的玻璃泡放在距离亮灯大约2 cm处,测出各自的温度.然后,把光敏电阻与电流表按图乙连成电路(该光敏电阻的阻值与光照强度成反比),再在暗室中将这三盏灯依次接入同一照明电路,并放在光敏电阻正上方30 cm处的同一位置,读出相应的电流,

根据他们的实验记录完成下列问题:

(1)电流通过电灯电能转化为______能和______能。

(2)电能转化为内能最多的是______灯;发光亮度最大的是______灯.

(3)从表中数据看出,灯附近的温度越低,图乙电路中电流表的示数就越__________,这说明灯将电能转化为光能越_____________.

(4)l5W的LED节能灯的发光亮度大约与_______W普通节能灯相当.

答案

(1)光能;内能(2)白炽灯;LED节能灯(3)大;多(4)60

题目分析:(1)用电器工作的过程,就是电流做功的过程,也是电能转化成其他形式能的过程;电流通过电能转化成光能和内能;

(2)电能转化为内能多说明在相等的时间内产生的热量多,即温度变化的多,由表中数据可见,在相等的时间内白炽灯使温度计示数上升的最多,故温度变化的也最多,所以电能转化为内能最多的是白炽灯.比较亮度可以比较光照的强度,光照强度与光敏电阻的阻值有关,阻值的大小可以由电流表的示数来判定.电流越大的电路中的电阻越小,又因为光敏电阻的阻值与光照强度成反比;所以电流表示数越大的光照强度越强,由表可知电流表示数最大的为LED节能灯,故发光亮度最大的是LED节能灯.

(3)由表中数据可知:LED节能灯的温度最低,而且电流表示数最大;电流表示数越大的,电阻阻值越小,则灯泡的光照强度也越强;因此灯附近的温度越低,图乙电路中电流表示数就越大,灯将电能转化为光能越多.

(4)灯越亮,灯产生的热量越少,温度越低,光敏电阻阻值越大,电流表示数越小,也就是说灯的亮度与电流表的示数成正比;因为相同功率的LED节能灯是普通节能灯光照强度的4倍,所以15W的LED节能灯的发光亮度大约与60W普通节能灯相当.故答案为:(1)光能;内能(2)白炽灯;LED节能灯(3)大;多(4)60.

阅读理解

阅读理解。

     Traveling to every part of the world gets easier, but how well do we know and understand each other. Here's a simple test. Imagine you are planning to hold  a  meeting at four  o'clock. What time  should you

expect your foreign business friends to arrive?  If  they  are  Germans,  they'll arrive on time.  If  they  are

Americans, they'll probably be  15  minutes early.  If they are Englishmen, they'll be 15 minutes late,  and

you should allow up to an hour for the Italians.

     The British seemed to think since the English language was widely used  in  the world,  people  would

always understand what they do.  However, they found they were completely wrong.  For example,  the

British are happy to have a business lunch and discuss business matters and have a drink during the meal.

The Japanese prefer not to work while eating.   Lunch is a time for them to relax and get  to  know  each

other and they don't drink at lunchtime. The Germans like to talk business before dinner. The French like

to eat first and talk afterwards. They have to be well fed and watered before they discuss anything.

1. What do the Germans prefer when they go to a meeting?

A. They prefer to be on time.

B. They prefer to arrive very early.

C. They prefer to arrive very late.

D. They prefer to arrive a little late.

2. According to the text, if a group of Englishmen, Americans and Italians hold a meeting, who will be the last to arrive? 

A. The Englishmen.

B. The Americans.

C. The Italians.

D. Both the Englishmen and the Italians.

3. What do the Japanese like to do at lunchtime?  

A. To drink.

B. To get to know each other.  

C. To talk business.

D. To eat only.

4. According to the writer, the British like to ________. 

A. arrive on time and talk business during the meal

B. arrive earliest and hate talking business at a meal

C. arrive 15 minutes late and talk business after the meal

D. arrive a few minutes late and discuss business during the meal

5. By giving us the two examples, the writer means to show us that _______. 

A. different countries have different cultures in different parts of the world

B. the Germans are more serious and have good living habits

C. the Italians are careless people and they are never on time for everything

D. the French people are very lazy. They prefer eating and drinking more

填空题