问题 实验题

实验桌上有三个完全相同的烧瓶,烧瓶内装有质量相等的煤油、型号相同的温度计和阻值相等且不变的电阻丝R,如图所示。另外,还有满足实验要求的电源、滑动变阻器和开关各一个,电流表和停表各一块,导线若干。请利用上述实验器材,设计一个实验证明:“保持电阻阻值不变,在相同时间内通过电阻的电流越大,电流通过电阻产生的热量越多”。实验设计中可用煤油升高的温度Δt的大小表示电流通过电阻丝R产生热量的多少。请画出实验电路图,写出实验步骤,画出实验数据记录表格。

答案

(1)首先电流表调零,观察各温度计,待三瓶液体的初温相同,记为t0

(2)如图连接电路,断开开关S,滑动电阻器在最大阻值处;

(3)闭合开关S,调节滑片P,使电流表示数为I1,同时按下停表,经过时间T之后,读取此时温度计示数为t1,将I1和t1记入表格;

(4)断开开关S,拆掉烧瓶甲,然后把烧瓶乙再串联在电路中,滑动电阻器调在最大阻值处;

(5)再闭合开关S,调节滑片P使电流表示数为I2,同时按下停表,经过时间T之后,读取此时温度计示数为t2,将I2和t2记入表格;

(6)仿照步骤(4)和(5),拆掉烧瓶乙,把烧瓶丙串联在电路中,读取电流表示数I3和t3,记入表格中;

(7)由△t1=t1-t0,△t2=t2-t0,△t3=t3-t0算出升高温度△t记入表格。

T/s   
I/A   
△t/℃   

题目分析:由于该题是让我们设计实验证明:保持电阻不变时,在相同时间内通过电阻的电流越大,电流通过电阻产生的热量越多;这是一个定性的关系而非定量,故我们只要做三次实验就可以了,由于题中给出了三个烧瓶,可见分别将这三个烧瓶接入电路中,用滑动变阻器改变电流,用电流表测其电流的大小,用温度计测在相同时间内煤油升高的温度即可,因为煤油升高的温度就代表了电阻产生的热量,而相同的时间可以通过秒表来控制。

阅读理解

     We Americans are wasteful people, not used to saving. Early settlers, our forefathers set us an

example of wasting everything, for they thought nature's resources were so plentiful that none of them

ever imagined that natural materials would be used up in time. Within a few years of the first Virginia

settlement, for example, pioneers burned down their house when they were ready to move west. They

burned down their house with only one aim to get the nails (钉子) for future use . No one ever gave a

thought to the priceless hard woods that went up in smoke. As a people we destroy many valuable

things that other people save. I noticed this when I was living in Britain. I received a letter from one

England's largest banks. It was enclosed in a used envelope that had been readdressed to me. Such a

practice would be unthinkable in the United States. American banks, even the smallest, always use

expensive stationery( 信笺) with the names of all twenty-eight vice-presidents lists on side of the page.

1. The used envelope suggests that______.

A. the English look down upon the Americans

B. the English banks are very poor

C. the English try their best to save

D. the English like using used envelopes

2. Which of the following statements is wrong?

A. The writer lives in Britain now.

B. The American banks use expensive stationery.

C. The Americans are not used to saving.

D. The writer's forefathers burned down their houses in order to get the nails.

3. The purpose of the passage is to _______.

A. wish the Americans not to waste    

B. tell us the English are a good people

C. warn the Americans against saving  

D. encourage people to work hard

单项选择题