问题 选择题

用控制变量法,可以研究影响电荷间相互作用力的因素.如图所示,O是一个带电的物体,若把系在丝线上的带电小球先后挂在横杆上的P1、P2、P3等位置,可以比较小球在不同位置所受带电物体的作用力的大小.这个力的大小可以通过丝线偏离竖直方向的角度θ显示出来.若物体O的电荷量用Q表示,小球的电荷量用q表示,物体与小球间距离用d表示,物体和小球之间的作用力大小用F表示.则以下对该实验现象的判断正确的是(  )

A.保持Q、q不变,增大d,则θ变大,说明F与d有关

B.保持Q、q不变,减小d,则θ变大,说明F与d成反比

C.保持Q、d不变,减小q,则θ变小,说明F与q有关

D.保持q、d不变,减小Q,则θ变小,说明F与Q成正比

答案

A、保持Q、q不变,根据库仑定律公式F=k

Qq
r2
,增大d,库仑力变小,则θ变小,减小d,库仑力变大,则θ变大.F与d的二次方成反比.故A、B错误.

    C、保持Q、d不变,减小q,则库仑力变小,θ变小,知F与q有关.故C正确.

    D、保持q、d不变,减小Q,则库仑力变小,θ变小,根据库仑定律公式F=k

Qq
r2
,知F与两电荷的乘积成正比.故D错误.

故选C.

完形填空

第二节:完形填空(共20小题;每小题1.5分,满分30分)

阅读下面短文,从短文后各题所给的四个选项(A、B、C和D)中,选出可以填入空白处的最佳选项,并在答题卡上将该项涂黑。

I’ve loved my mother’s desk since I was just tall enough to see above the top of it as mother sat doing letters. Standing by her chair, looking at the ink bottle, pen, and white paper, I decided that the act of ___21___ must be the most ___22___ thing in the world.

Years later, during her final illness, mother ___23__ different things for my sister and brother. “But the ___24___”, she said, “is for Elizabeth”.

I never saw her angry, and never saw her cry. I knew she ___25___ me, she showed it in action. But ___26___ a young girl, I wanted heart-to-heart talks ___27___ mother and daughter. They never happened. And a gulf(深渊) opened between us. I was “too emotional”. ___28___ she lived “on the surface”.

As years passed and I graduated from college, I loved my mother and I wrote to her in ___29__ words and asked her to let me know in any way she chose that she did ___30___ me.

I posted the letter and waited for her answer. ___31___ came. My hope turned to ___32___, then little interest, finally, peace --- it seemed that nothing happened. I couldn’t be sure that the ___33___ had even got to Mother. I only knew that I had written it, and I could ___34___ trying to make her into someone she was not.

Now the ___35___ of her desk told me, as she’d ___36___ been able to, that she was ___37___ that writing was my chosen work. I ___38___ the desk carefully and found some papers ___39___---- a photo of my father and a one-page letter, folded and refolded many times.

“Give me an answer”, my letter asks, “in any way you chose”. Mother, you always chose the ___40___ that speaks louder than words.

21. A.Speaking         B.writing                   C.looking                  D.listening

22. A.Wonderful       B.tiring                     C.funny                    D. Productive

23. A. bought               B. gave                        C. designed                  D. kept

24. A. pen                    B. paper                       C. chair                       D. desk

25. A. loved                 B. disliked                   C. appreciated              D. sympathized

26. A. like                   B. as                        C. be                        D. unlike

27. A. with                  B. among                     C. beside                     D. between

28. A. So                     B. And                         C. But                     D. Or

29. A. careful               B. active                      C. thankful                  D. serious

30. A. ignore                B. accept                      C. forgive                    D. dislike

31. A. No one              B. None                    C. Something               D. Neither

32. A. surprise           B. joy                       C. disappointment         D. happiness

33. A. ides                   B. information              C. news                       D. letter

34. A. stand                 B. stop                         C. continue                D. practice

35. A. present               B. appearance               C. shape                      D. sight

36. A. always               B. ever                        C. never                      D. often

37. A. sorry                 B. encouraged              C. regretful                  D. pleased

38. A. moved               B. cleaned                 C. fixed                       D. emptied

39. A. inside                B. outside                    C. below                      D. above

40. A. gesture               B. method                    C. action                   D. way

判断题