问题 问答题

小明同学把两个额定电压相同的小灯泡串联在电路中,如图所示,他发现L1比L2亮,于是他认为L1的额定功率比L2的大.请你设计一个实验,证明他这种说法是否正确.(设灯丝电阻不变)

(1)在如图所示的器材基础上,要完成实验,还需要的器材有______.

(2)简述实验操作步骤______.

(3)分析与结论______.

答案

(1)要测量电功率,需要用到电流表和电压表分别测出电流和电压,根据公式P=UI计算得出;

(2)(3)将电流表串联在电路中,测出电路中的电流,便可知两灯泡的电流I;

分别将电压表与两灯泡并联,测出两灯泡两灯泡两端的电压U1、U2,则可根据P1=U1I、P2=U2I计算出功率比较得出结论;

故答案为:(1)电流表、电压表;

(2)①把调节好的电流表串联在电路中,测出电路中的电流为I,记录在表格中;

②把调节好的电压表分别并联在L1、L2两端,测出它们两端的电压分别为U1、U2,记录在表格中;

③利用R=

U
I
分别算出L1、L2的阻值为R1、R2

(3)利用P=

U2
R
(或P=UI)分别算出L1、L2的额定功率为P1、P2,比较P1、P2的大小,从而证明小明的说法是否正确.

阅读理解

阅读下面短文,简要回答所给问题。

It was near Christmas during my first semester teaching at a new school.I loved my small special class more than any group I had taught in the past.They were hungry for knowledge and I was enjoying teaching.

Other teachers had told me that our children were from poor families and not to expect any child to bring a Christmas gift.In fact,I wasn't expecting any gifts.

Imagine my surprise when every child brought me a gift on the day before our holiday break.First,I got a much­loved stuffed monkey from a shy girl.I was told,“He is my favorite,but I love you and I want him to be with you,Miss Taylor.”How thrilled I was!

Next came a new set of Christmas tree lights that was “missing” from a mother's cupboard.

Finally,I came to one little boy's gift which I had never received.It was an old,dirty and broken Christmas story book.Just when I wanted to express my happiness,I was interrupted(打断)by the giver,“And see,it is new!It still has the price tag.”

When other children laughed at him,I stopped them and said,“Oh,books are good in that way.The story is always new if you have not read it before.Now,let's share one together.”Everyone listened quietly as I read the most wonderful Christmas story of my life.

I still keep those Christmas gifts.They always remind me of my lovely kids.

小题1:Why did the teacher like her small special class?

____________________________________________________

小题2:When did the children bring their teacher gifts?

__________________________________________________________

小题3:Who sent a stuffed monkey to the teacher?

_______________________________________________________

小题4:Was the Christmas story book new?

________________________________________________________

小题5:How did the teacher feel when she got the gifts?

单项选择题