问题 问答题

同学们知道,将两个金属电极插入任何一个水果中就可以做成一个水果电池,但日常生活中我们很少用“水果电池”,这是为什么呢?某学习小组的同学准备就此问题进行探究.

(1)同学们通过查阅资料知道将锌、铜两电极插入水果中,电动势大约会有1伏多一点.晓宇同学找来了一个土豆做实验,当用量程为0~3V、内阻约50kΩ的伏特表测其两极时读数为0.96V.但当他将四个这样的水果电池串起来给标称值为“3V,0.5A”的小灯泡供电时,灯泡并不发光.检查灯泡、线路均没有故障,而用伏特表测量其电压确实能达到3V多.据您猜想,出现这种现象的原因应当是:______(不要求写分析、推导过程).

(2)晓宇同学用欧姆表直接测“土豆电池”的两极,读得此时的读数为30Ω.小丽同学用灵敏电流表直接接“土豆电池”的两极,测得电流为0.32mA,根据前面用伏特表测得的0.96V电压,由全电路欧姆定律得:r=

E
I
=
0.96
0.32×10-3
Ω=3.0kΩ.因而晓宇同学说土豆的内阻为30Ω,而小丽同学则说是3kΩ.请你判断,用晓宇或小丽同学的方法测量“土豆电池”的内阻,结果是否准确,为什么?请分别说明理由.

(3)若实验室除了导线和开关外,还有以下一些器材可供选择:

A.电流表A1(量程为0~0.6A,内阻为1Ω)

B.灵敏电流表A2(量程为0~0.6mA,内阻为800Ω)

C.灵敏电流表A3(量程为0~300μA,内阻未知)

D.滑动变阻器R1 (最大阻值约10Ω)

E.滑动变阻器R2(最大阻值约2kΩ)

F.定值电阻(阻值2kΩ)

G.变阻箱(0~9999Ω)

①为了能尽可能准确测定“土豆电池”的电动势和内阻,实验中应选择的器材是______(填器材前的字母代号).

②在右方框中画出应采用的电路.

答案

(1))“苹果电池”的内阻太大,接灯泡时,电流太小,灯泡功率太小,不会发光;

故答案为:“苹果电池”的内阻太大;

(2)晓宇的方法不正确,因水果电池本身有电动势,当用欧姆表直接接“土豆电池”的两极时,欧姆表内部的电源与水果电池的电动势正向或反向串联,影响测量的结果,故测不准;

小丽同学测量的误差也很大.理想状态下用电流表测得的是短路电流,伏特表测得的应当是电源电动势,但由于水果电池的内阻很大,伏特表的内阻不是远大于水果电池的内阻,故其测得的电动势误差大,算得的内阻亦不准确.

小丽同学的测量为扣除电流计内电阻;

(3))①安阻法测电源电动势与内阻需要电阻箱与电流表,由题意可知,水果电池内阻很大,通过水果电池的最大电流较小,为保证安全并精确测量,电流表可选B、灵敏电流表A2(量程为0~0.6mA,内阻为800Ω),因此实验器材可选:B、G.

②安阻法测电源电动势与内阻的实验电路图如图所示.

故答案为:(1)水果电池的内阻太大.

(2)晓宇的方法不正确,因水果电池本身有电动势,当用欧姆表直接接“土豆电池”的两极时,欧姆表内部的电源与水果电池的电动势正向或反向串联,影响测量的结果,故测不准.

小丽同学测量的误差也很大.理想状态下用电流表测得的是短路电流,伏特表测得的应当是电源电动势,但由于水果电池的内阻很大,伏特表的内阻不是远大于水果电池的内阻,故其测得的电动势误差大,算得的内阻亦不准确.

(3)①B,G;②如图所示.

阅读理解

One day when some government officials were rebuilding a barn(谷仓), they found a mouse hole in a corner and they used smoke to force the mice inside the hole to come out. A while later they indeed saw mice running out, one after another. Then, everyone thought that all the mice had ran away. But just as they began to clean up, they saw two mice squeezing(挤)out at the mouth of the hole. With some efforts, the mice finally got out. However, it was strange that after they came out of the hole, they did not run away immediately. Instead, one ran after the other near the mouth of the hole. It seemed that one was trying to bite the tail of the other.

Everyone was puzzled, so they stepped nearer to take a look. They realized that one of the mice was blind and could not see anything, and the other was trying to allow the blind mouse to bite on his tail so that he could pull the blind one with him to run away.

After seeing what happened, everyone was silent and lost in thought. During the meal time, the group of people sat down in a circle and started to chat about what happened to the two mice.

One serious American official said: "I think the relationship between those two mice was that of king and guard." The others thought for a while and said: "That was why!"

A smart French said: "I think the relationship between those two mice was that of husband and wife." Again the others thought for a while, and all felt it meaningful.

A Japanese said: "I think the relationship between those two mice was that of mother and son." Once again the others thought for a while, and felt this was more reasonable. So they expressed agreement another time.

At that moment, one Chinese asked: "Why did those two mice have to have a certain relationship?"

Suddenly, the group looked back at the Chinese and didn't say any words. The American official, the French and the Japanese who had spoken earlier all lowered their heads in shyness, and did not dare to answer.

In fact, the true love is not built on friendship, loyalty(忠诚) or blood relationship. Instead, it is based on no relationship.

小题1:Neither of the two mice ran away immediately because_______.

A.one was trying to help the blind one

B.one was biting the other

C.the mouth of the hole was too small

D.they were not afraid of smoke小题2:Why did they lower their heads in shyness according to the passage?

A. Because they did not dare to answer.

B. Because they regretted(后悔)driving a poor blind mouse away.

C. Because they had mistaken the relationship of the mice.

D, Because they did not express themselves much better.

小题3:It is clear that_______.

A.all the mice came out of the hole easily

B.each of the people understood the relationship differently

C.the people wanted to kill the mice with smoke

D.the people knew one of the mice was blind at the first sight小题4:The best title for the passage is_______.

A.Two lovely mice

B.Help produces love

C.Love is all

D.Friends in need

判断题