问题 填空题

在图8所示的电路中,电源电压保持不变。闭合电键S,当滑动变阻器的滑片P自左端向中点移动时,电压表V的示数将   19   ,电流表A与电流表A1示数的差值将   20   。(均选填“变大”、“不变”或“变小”)

 

答案

不变;不变

析:从图可知,滑动变阻器R2与定值电阻R1串联,电流表测量的是整个电路中的电流,电压表V1测量的是电源电压,电压表V2测量滑动变阻器两端的电压.根据欧姆定律和串联电路电压特点表示出滑动变阻器两端的电压,当滑动变阻器的滑片P自左端向中点移动时,得出电压表V2的示数变化和电路中电流之间的关系,再根据定值电阻的阻值不变判断电压表V2示数的变化值与电流表A示数变化值的比值的变化.

解答:解:因电源的电源U不变,电压表V1的实数不变;

又因电压表V2测量的是滑动变阻器两端的电压U2

根据串联电路电压特点和欧姆定律可知U2=U-U1=U-IR1

当滑动变阻器的滑片P自左端向中点移动时,

电压表V2的示数变化为△U2=△IR1,即=R1

因定值电阻R1的阻值不变,所以电压表V2示数的变化值与电流表A示数变化值的比值不变.

故答案为:不变;不变.

完形填空

One Saturday afternoon, Kate went to buy something for her sister and herself.
As Kate was coming out of a 1, a young lady walked towards her. She said she was Miss Green --- a good friend of Kate’s sister. Kate 2 her. Then she called a taxi to send Kate home. She 3 the driver where he should go. Kate was 4 that it was not the in direction of her home.
5?” Kate asked. The lady smiled.
When they came to a quiet road, a big rough man 6, on the road. He stopped the taxi driver, knocked him down, and threw him out of the 7. At the same time, Miss Green took out of a knife and 8 it at Kate. She asked Kate to keep 9. The man then started the taxi.
“ Oh, my God! I’m being kidnapped,” Kate said to herself.
She tried to escape, but not 10. Suddenly an 11 came to her. She took out a lipstick(口红) from her pocket, wrote ‘SOS’ on the window, and covered the word with her 12.
A few minutes later, a police car 13 and the policemen saw the sign. When the kidnappers saw the policemen they stopped the taxi, jumped into the grass, and ran away.
The policemen then 14 Kate up and sent her home. When her parents knew what had happened, they were greatly surprised. But they were also 15 because their daughter had finally come back safely.
小题1:
A.schoolB.taxiC.shopD.friend’s
小题2:
A.knewB.believedC.thankedD.remembered
小题3:
A.toldB.askedC.wonderedD.checked
小题4:
A.sureB.excitedC.surprisedD.pleased
小题5:
A.WhatB.WhereC.WhenD.Why
小题6:
A.droveB.climbedC.fellD.appeared
小题7:
A.roadB.sightC.taxiD.home
小题8:
A.shoutedB.playedC.hurtD.pointed
小题9: 
A.healthyB.aliveC.relaxedD.quiet
小题10:
A.happenedB.failedC.succeededD.hurried
小题11:
A.ideaB.answerC.interestD.order
小题12:
A.handsB.backC.dressD.lipstick
小题13:
A.soppedB.leftC.passedD.turned
小题14:
A.liftedB.heldC.putD.picked
小题15:
A.worriedB.happyC.proudD.successful
填空题