题干

图所示电路中,电源两端电压保持不变,在电路中M、N两点间接入一只标有“2.5V 0.75W”的小灯泡L1,闭合开关S,调节滑动变阻器滑片,使L1恰好正常发光.保持滑动变阻器滑片位置不变,若在M、N两点间换接另一只标有“2.5V 2W”的小灯泡L2(L1和L2的灯丝电阻均保持不变),下列说法中正确的是(  )

A:电流表的示数为0.3A

B:L2可能不发光或发出较暗的光

C:L2的实际功率大于2W

D:要使L2正常发光,需将滑动变阻器滑片适当向右调节

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答案(点此获取答案解析)

B

同类题5

七选五。根据短文内容,从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。

    My mother is a diligent and kind woman. She is very busy from morning till night. As a teacher, she works hard. ____Both my brother and I love her dearly as she loves us.

    My mother has been teaching math at a middle school in my hometown. She goes to work early in the morning and does not return home until late in the afternoon. ____She treats them with patience and teaches them well. For her excellent quality and very good teaching results, she has been elected as a model teacher several times.

    ____ Every day, when she comes back home from work, she sets about doing housework, sweeping the living room and bedrooms or cleaning the furniture, and putting everything in good order. She seems to be busy all the time. As she has been very busy working every day, she looks older than her age. But she looks as cheerful and happy as ever. Mother never buys expensive dresses for herself, but she often buys some inexpensive but high quality clothes for us. ____She just eats a plain meal outside when she is too busy to cook herself. She lives a busy yet simple life, without any complaints.

    Often she says to us, “work while you work, and play while you play. That is the way to be happy and gay. If you do not work, you will become lazy and be of no use to society”. What a piece of good advice this is! ____This advice of hers will always serve as a guide to my behavior. My mother is great indeed, and I always feel proud of her.

A. She enjoys listening to classic music.

B. As a mother, she takes good care of us and gives us every comfort.

C. She loves her students and cares for them.

D. She never goes to expensive restaurants to enjoy meals.

E. My mother is hard-working and never wastes money.

F. I never forget it and always bear it in my mind.

G. Can you tell us something about your mother?