题干

如图电路中,电源电压保持不变.闭合开关S,当滑片移到滑动变阻器的b端时,电压表的示数为8伏,10秒内定值电阻R1做功为20焦;当滑片P移到滑动变阻器的中点时,电压表的示数为6伏.下列结果正确的是(  )

A:电源电压为14伏

B:滑动变阻器R的最大阻值为8欧

C:滑片在b端,电流表示数为0.75安

D:电路先后两次消耗的总电功率之比为2:3

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D

同类题5

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。选项中有一项为多余选项。                                                            

     Why do we play sports? You might say “to get exercise” and you'd be right. To have fun? That's true, too. But there's more. ____ According to a study, girls who play sports get a lot more than just fit.

  Girls who play sports do better in school. You might think that playing sports will take up all your study time. ____  Exercise improves learning, and memory, which can give active girls an advantage in the classroom.

Girls who play sports learn teamwork and goal-setting skills. ____ When you work with coaches, trainers, and teammates to win games and achieve goals, you're learning how to be successful. Those skills will serve you well at work and in family life.

  Playing sports improves self-confidence.  ____ Why? It builds confidence when you know you can practice, improve, and achieve your goals. Sports are also a feel-good activity because they help girls get in shape, keep a healthy weight, and make new friends.

  ____ Playing sports can reduce stress and help you feel a little happier. How? The brain chemicals released during exercise improve a person's mood. Friends are another mood-lifter.And being on a team creates tight bonds between friends. It's good to know your teammates will support you-both on and off the field!

A. Exercise cuts the pressure.

B. Sports teach valuable life skills.

C. In fact, there are at least 4 more reasons.

D. Girls who play sports feel better about themselves.

E. Plying sports offers children more than just physical benefits.

F. But research shows that girls who play sports do better in school than those who don't.