问题 选择题

如图所示的电路,电源电压和灯泡电阻都保持不变,当滑动变阻器R的滑片P由中点向右移动时,下列判断中正确的是(  )

A.电流表和电压表的示数都增大,灯变亮

B.电流表和电压表的示数都减小,灯变暗

C.电流表的示数减小,电压表的示数增大,灯变暗

D.电流表的示数减小,电压表的示数不变,灯的亮度不变

答案

(1)分析电路结构,画出等效电路图如图所示;

(2)由等效电路图知电压表测并联电压,即电源两端的电压,

由于电源电压U不变,所以,滑动变阻器滑片向右移动时,

电压表示数不变,滑片向右移动,滑动变阻器接入电路的阻值R变大,

由I=

U
R
知:流过滑动变阻器的电流变小,电流表示数变小;

由于灯泡两端电压不变,灯泡电阻不变,则灯泡的功率P=

U2
R
不变,灯泡亮度不变;

故选D.

完形填空

A seeker asks, “I want to make a difference in the world, but there are so many causes crying for attention that I feel deeply confused. I don't know where to put my energy to have the greatest   21 . Where do I begin?”

Lynn Answers:

There is no one “  22 ” place to begin. Each of us has a different   23 place, and the place where we will be of greatest service has to do with where we most want to   24 . If we want to have an effect on the world around us, it's important to   25 what I think of as our "Area of Power." Our Area of Power is where we feel the most passion to act and have the most   26 that results are   27 .

If we pray for world peace, but have no vision of what this would look like and no faith that our   28 will help, our effect is less than if we pray for peace and harmony in our own   29  with a clear picture of what this means and excitement that healing is possible. Without faith that we can   30 , our power to help is decreased.

21. A. power             B. ease                 C. effect                    D. result

22. A. right           B. real                      C. similar                D. exact

23. A. amusing          B. ending                 C. starting                    D. finishing

24. A. give           B. live               C. act                   D. dream

25. A. work              B. regard              C. consider                  D. identify

26. A. power             B. peace               C. faith                   D. energy

27. A. visible        B. possible            C. reasonable         D. accessible

28. A. prayers          B. players            C. seekers                D. watchers

29. A. language         B. way                 C. world                      D. family

30. A. make an effort                          B. make it               

C. make a difference                            D. make ends meet

单项选择题