如图所示，电源电压为6V不变，R1的电阻为12Ω R2的电阻为9Ω，求
（1）开关S2闭合，S1、S3同时断开时，两表的示数分别为多少？
（2）开关S2断开，S1、S3同时闭合时，两表的示数是分别为多少？
1）开关S2闭合，S1、S3同时断开时，R1和R2串联，
电流的大小有：I=
=U R1+R2
=0.29A；6v 12Ω+9Ω
电压表示数：U1=IR1=0.29A×12Ω=3.48v
2）开关S2断开，S1、S3同时闭合时，R1和R2并联，电压表测的仍是电源电压，
所以通过R1的电流：I1=
=U R1
=0.5A．6v 12Ω
答：1）两表的示数分别3.48v，0.29A；2）两表的示数是分别6v，0.5A．
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| The inspector (检查员) of Schools arrived yesterday morning, and he 1 the whole day examining the classes. The headmaster had told us a few days 2 that he was coming. I thought the headmaster was very nervous 3 it, for every day, he came to all the classes, 4 the teachers over and over again what they must do and examined the boys himself to see whether they were 5 for the inspection. He told us in our 6 that we were all fools and would be sure to 7 him lose face before the Inspector. All 8 made us very nervous; and when the Inspector wandered into our class, we were all 9 with fright. I felt all that I 10 knew had been clean forgotten. The Inspector was a tall man. He wore glasses and always 11 very strict. He kept examining the class in English and I was asked to read. I felt very 12 but somehow I managed to get through without any mistakes. Some of the other boys, 13 did not do well and the Inspector looked even more serious than usual, though he did not say 14 . We got along better with History and Geography; but when it came to Maths, he set us to some very 15 problems which we 16 to do; so he looked very black at our teacher. Our teacher was very 17 with us afterwards; but I am sure we should have done 18 if we had not been so 19 . I think I should like to be an inspector when I 20 up. Then everyone would have to be afraid of me! | ||||
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