问题 实验题

(5分)在做“测定金属丝的电阻率”的实验中,若待测电阻丝的电阻约为5,要求测量结果尽量准确,提供以下器材供选择:

A.电池组(3V,内阻约1

B.电流表(0—3A,内阻约0.0125

C.电流表(0—0.6A,内阻约0.125

D.电压表(0—3V,内阻约4 k

E.电压表(0—15V,内阻约15 k

F.滑动变阻器(0—20,允许最大电流1A)

G.滑动变阻器(0—2000,允许最大电流0.3A)

H.开关、导线若干

(1)实验时电流表、电压表和滑动变阻器应分别选取                              .(填写仪器前字母代号)

(2)测电阻时,电流表、电压表、待测电阻在组成测量电路时,应采用电流表       (选填“内”或“外”)接法,测量值比真实值偏         (选填“大”或“小”)

答案

(1)   C  D  F      (2)    小  

题目分析:解决本题的关键是掌握器材选取的原则,以及知道电流表内外接的区别,会进行误差分析.

(1)通过安全、精确的原则选择电流表、电压表的量程以及滑动变阻器.由于电动势是3 V,用3 V量程的电压表D;因为电阻丝的电阻大约为5Ω,如果把3 V的电动势全加在电阻丝上,电流才是0.6 A,因此用量程是0.6 A的电流表C;此题中金属丝的电阻大约为5Ω,为了减小实验误差,应选10Ω的滑动变阻器F,所以实验时电流表、电压表和滑动变阻器应分别选取CDF;

(2)因为待测电阻与电流表和电压表内阻相比较,远小于电压表的内阻,属于小电阻,属于电流表采用外接法误差较小.此时由于电压表起分流作用,电流表测量通过电阻的电流偏大,根据欧姆定律,则测量值比真实值偏小.

阅读理解

阅读理解。

     Three key facts about rising sea levels need to be pointed out to the world's politicians and planners:

sea-level rise is now unavoidable (不可避免的), it will happen faster than most of us thought, and it will

go on for a very long time.

     Even if greenhouse gas emissions (排放) stopped tomorrow, the oceans would continue to become

larger as they get warm. The climate scientists estimate that sea-level rise may be in the range of 1 to 2

meters by 2100, with a small risk of an even greater rise.

     For many islands and low-lying regions, even small rises will cause disasters. But for most countries,

the problem is what has been built on that land: New York, Sydney and Tokyo, to mention just a few

cities. Unless something can be done, great areas of urban network will disappear under the waves. It

will take a great engineering effort to protect these cities-an effort that may be beyond economies that

have been brought to their knees.

     None of this means we should fear, and stop trying to forbid emissions. But together with these efforts,

we need to start acting now and we must stop building in danger zones.

     Billions of dollars are being spent on constructing homes, offices and roads in vulnerable (脆弱的)

coastal areas. For instance, the skyscrapers of Shanghai are being built on land that is mere 4 meters

above sea level on average, and they are sinking under the weight of the buildings. Therefore, planning

for new coastal developments is to go against reality. If we want to build a lasting heritage for our children,

we should do so on the plentiful land that is in no danger from the sea. It is one of the effective ways to

slow down climate change, and we should be acting on it now.

1. The most possible reason for the rising of sea levels should be _____.

A. greenhouse gas emission

B. temperature change of the oceans

C. vulnerable coastal area

D. fast urban development and expansion

2. New York, Sydney, and Tokyo are mentioned in this passage to show _____.

A. climate change has been completely out of control

B. modem cities are usually built along the coastline

C. the coastline is very important for modem countries

D. climate change can do harm to economies

3. The effort to protect coastal cities may be beyond economies because _____.

A. much money has been wasted to build coastal cities

B. people have lost confidence in their economies

C. economy development has made climate change worse

D. protecting the cities may cost more than what has been obtained

4. According to the author, we should _____ to deal with sea-level rise.

A. move big cities like New York and Shanghai to higher places

B. stop building skyscrapers in big cities like Sydney and Tokyo

C. build cities on the land free from the danger of sea-level rise

D. be aware of the danger of greenhouse gas emissions into the ocean

填空题