为测量一只标有“6.3V0.3A“的小灯泡的额定功率，某实验小组设计_爱下问搜题

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问题问答题

为测量一只标有“6.3V0.3A“的小灯泡的额定功率，某实验小组设计了如图的电路图．现有实验器材为：电压表（量程0～3V，0～15V）一块．电流表（量程0～0.6A，0～3A）一块，“10Ω 2A“和“50Ω 1A“的滑动变阻器各一只，电源（电压恒为12V）一个，开关一只，导线若干．实验时，甲同学认为电压表和电流表都应选用小量程，滑动变阻器应选用“50Ω 1A“的；乙同学认为电压表应选用大量程，电流表应选用小量程，滑动变阻器应选用“10Ω2A“的．

请你对两位同学器材选择的合理性作出评价并填在表中

	是否合理	不合理之处	不合理产生的后果
甲
乙

（如合理，不需说明理由；如不合理，请指出不合理之处和产生的后果）．

答案

额定电压为6.3V，电压表选择0～15V量程．

灯泡的额定电流为0.3A，电流表选择0～0.6A量程．

灯泡正常工作时，滑动变阻器电压为：U=U_总-U′=12V-6.3V=5.7V，

所以滑动变阻器电阻为：R=

U

I

=

5.7V

0.3A

=19Ω，

所以“10Ω 2A”的滑动变阻器不能满足实验要求，

所以应选择“50Ω 1A”的滑动变阻器．

甲选择的电压表量程太小，被测电压超过电压表量程，会损坏电压表，

乙选择的滑动变阻器电阻太小，电路电阻太小，电流过大，会烧坏电流表或灯泡或电压表．

故答案为：

	是否合理	不合理之处	不合理产生的后果
甲	不合理	电压表量程太小	可能损坏电压表
乙	不合理	滑动变阻器阻值过小	可能损坏小灯泡

判断题

从发生疯牛病的国家或地区进口化妆品，报检时须提供输出国家或地区的官方的动物检疫证书，证明其中不含牛、羊的脑及神经组织、内脏、胎盘和血液(含提取物)等动物源性成分或所含的上述成分来自于健康的牛、羊。 ( )

完形填空

“Down-to-earth” means someone or something that is honest, practical and easy to deal with. It is   36  to find someone who is down-to-earth. A person who is down-to-earth is easy to talk to and   37  other people as equals. A down-to-earth person is just the   38  of someone who acts important and proud.
Down-to-earth persons   39  be important members of society, of course.   40 they do not let their importance “go to their heads”. They do not   41  themselves to be better persons than others of less importance. Someone who is filled with his own importance and pride, often without cause, is   42  to have “his nose in the air”. There is   43  way a person with his nose in the air can be down-to-earth.
Americans   44  another expression that means almost the same as “down-to-earth”. The expression is “both-feet-on-the-ground”. Someone with both-feet-on-the-ground is a person with a good   45  of reality. He   46  what is called “common sense”. He may have   47 , but he does not allow them to   48  his knowledge of what is real.
The opposite kind of   49  is one who has his “head-in-the-clouds”. A man with his-head-in-the-clouds is a dreamer whose   50  is not in the real world.
51 , such a dreamer can be brought back to earth.   52  words from a teacher can usually bring a day-dreaming student down-to-earth.
Usually, the person who is down-to-earth is very   53  to have both feet on-the –ground. 54  we have both our feet on-the –ground, when we are down-to-earth, we act   55  and openly towards others. Our lives are like the ground below us, solid and strong.

A．understanding

D．expectation

C．achievements

D．disadvantages