利用伏安法测量干电池的电动势和内阻，现有的器材为：
干电池：电动势约为1.5 V，符号
电压表：量程1 V，内阻998.3 Ω，符号
电流表：量程1 A，符号
滑动变阻器：最大阻值10 Ω，符号
电阻箱：最大阻值99999.9 Ω，符号
单刀单掷开关一个，符号
导线若干
(1)设计测量电源电动势和内阻的电路并将它画在下面的方框内．要求在图中标出电压
表、电流表的接线柱的正负．
(2)为了满足本实验要求并保证实验的精确度，电压表量程应扩大为原量程的
____________倍，电阻箱阻值为____________ Ω.
(1)见解析图 (2)2 998.3
(1)电源电动势为1.5 V，而电压表最大量程为1 V，需将电压表扩大量程再用，故
电压表应与电阻箱串联使用，设计电路如右图所示．
(2)为保证实验精确度，应将电压表量程扩大为2 V，即原来的2倍，由
＝
可知，
R＝RV＝998.3 Ω.
| 完形填空。 | ||||
| Man has a big brain (脑). He can think, learn and speak. Scientists once thought that men are different from animals 1 they can think and learn. They know now that dogs, monkeys, birds can learn, too. They are beginning to understand that men are different from animals because they can speak. Animals can't speak. They make noises when they are afraid, or unhappy. Apes (类人猿) can understand some things 2 than man. One or two of them have learned 3 words. But they can not join words to make sentences. They cannot think 4 us because they have 5 language. Language is a wonderful thing. Man has 6 build a modern world because he has language. 7 child can speak his own language very well when he is four or five, 8 no animals learn to speak. 9 do children learn it? Scientists don't really know. 10 happens inside our body when we speak? They don't know. They only know that man can speak because he has a brain. | ||||
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