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某同学利用电压表和电阻箱测定一种特殊电池的电动势 （电动势E大约在9V左右，内阻r约为50Ω），已知该电池 允许输出的最大电流为l50mA．该同学利用如图（a）所示的电路进行实验，图（a）中电压表的内阻约为2KΩ，R为电阻箱．阻值范围0～9999Ω，R0是定值电阻，起保护电路的作用．

（1）实验室备有的定值电阻尺．有以下几种规格：

A．2Ω    B．20Ω    C．200Ω  D．2000Ω，本实验应选______（填入相应的字母）作为保护电阻．

（2）在图（b）的实物图中，已正确地连接了部分电路，请完成余下电路的连接．

（3）该同学完成电路的连接后，闭合开关s，调节电阻箱的阻值；读取电压表的示数，其中电压表的某一次偏转如图（c）所示，其读数为______．

（4）改变电阻箱阻值，取得多组数据，作出了如图（d）所示的图线，则根据该同学所作出的图线可求得该电池的电动势E为______V，内阻r为______Ω．（结果保留两位有效数字） （5）用该电路测电动势与内阻，测量和真实值的关系E测______E真，r测______r真（填“大于”、“小于”或“等于”）

答案

（1）当电阻箱的电阻调为零时，电路中电流最大，根据闭合电路欧姆定律得

    Im=

E
R0+r

得R0=10Ω

所以实验应选B．

（2）根据电路图连接实物图，电动势E大约在9V左右，电压表应选择15V的量程，如图：

（3）电压表应选择15V的量程，所以读数为6.5V，

（4）闭合开关，调整电阻箱的阻值，读出电压表的示数，再改变电阻箱的电阻，得出多组数据．根据

1
U
=
1
E
+
r
E
1
R0+R
，知图线的纵轴截距表示电动势的倒数，图线的斜率等于
r
E
．

有：

1
E
=0.1，解得E=10V．

r
E
=5，解得r=50Ω．

（5）如果考虑电压表的内阻，根据实验的原理E=U+（

U
R0+R
+
U
Rv
）r，得：
1
U
=
1
E
（1+
r
Rv
）+
r
E
?
1
R0+R
，

考虑电压表的内阻，此时图线的纵轴截距表示

1
E
（1+
r
Rv
），所以E测小于E真，r测小于r真．

故答案为：（1）B．（2）（3）6.5 v  （4）10，50Ω  （5）小于，小于

阅读理解
Reading is a good habit, but the problem is there’s too much to read these days and too little time to read every word of it. There are hundreds of skills to help you read more in less time. Here are two skills that I think are especially good.
Preview — if it’s long and hard. Previewing is especially useful for getting a general idea of heavy reading like long magazine articles and business reports.
Here’s how to preview.
Read the first two paragraphs and the last two paragraphs carefully.
Then read only the first sentence of the other paragraphs.
Previewing doesn’t give you all the details. It keeps you from spending time on things you don’t really want － or need － or read.
Skim － if it’s short and simple. Skimming is a good way to get a general idea of light reading like popular magazines or the sports and entertainment of your daily paper.
Here’s how to skim.
Get your eyes to move fast. Sweep them across each line.
Pick up only a few key words in each line.
Everybody skims differently. You and I may not pick up the same words when we skim the same piece, but we’ll get a similar idea of what it’s all about.
小题1: How many skills does the writer introduce to help us in reading?
A．One.B．Two.C．Three.D．Four.
小题2: What should you do if you read a long article according to the writer?
A．Read every word of it.B．Read all the details.
C．Pick up a few key words in each line.
D．Read the first and the last two paragraphs carefully.
小题3: If you read a simple article, which reading skill is better to get the general idea?
A．Previewing.B．Skimming.C．Reading.D．Sweeping.
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材料分析题

材料一：当我国经济增长由偏快转为过热，价格上涨压力加大时，面对通货膨胀苗头的不断加剧，国家通过减少经济建设支出，增加了对房地产企业的税负，降低部分商品出口退税率等措施，稳定物价，促进国民经济健康发展。

材料二：2009年世界经济金融危机日趋严峻，为抵御国际经济环境对我国的不利影响，国家采取灵活审慎的宏观经济政策，以应对复杂多变的形势。如连续多次下调人民币利率和存款准备金率、提高部分商品出口退税率、下调证券（股票）交易印花税税率并改为单边征收、暂免征收个人储蓄存款利息所得税，以及高达4万亿元投资的经济刺激方案等等，都体现了国家努力刺激需求增长、拉动经济发展的决心。

结合上述材料，运用所学的《经济生活》的知识说明国家财政政策是如何控制国民经济平稳运行的？

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