题干

如图所示的电路中,电源电压和灯泡电阻都保持不变,闭合开关S,滑动变阻器的滑片P由中点向右移动时,下列判断正确的是(  )

A:电压表和电流表的示数都增大,电路总功率变大

B:电压表和电流表的示数都减小,电路总功率变小

C:电流表示数增大,电压表示数变大,灯泡变亮

D:电流表示数变小,电压表示数不变,灯泡亮度不变

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答案(点此获取答案解析)

D

同类题1

    One afternoon, my son came home from school and asked me, “Are all people the same even if their skin color is different?” I thought for a moment, then I said, “I'll explain. Let's go to a fruit store first. I have something interesting to show you.”
At the store, I told him that we needed to buy apples. And we bought some red apples, green apples and yellow apples.
   After we got home, I told Adam, “It’s time to answer your question.” I put one of each type of apple on the table: first a red apple, followed by a green apple and then a yellow apple. Then I looked at Adam, who was sitting on the other side of the table.
   “Adam, people are just like apples. They come in different colors, shapes and sizes. See, some may not even look as delicious as others.” As I was talking, Adam was examining each one carefully.
   Then, I took each of the apples and peeled them, placing them back on the table, but in a different place.“OK, Adam, tell me which one is the red apple, the green apple and the yellow apple.”He said, “I can’t tell. They all look the same now.”“Take a bite(一口) of each one. See if that helps you tell which one is which.”He took big bites, and then a huge smile came across his face. “People are just like apples! They are all different, but if you take off the outside, they’re pretty much the same on the inside.”“Right,” I agreed. “Just like everyone has their own features but they are nearly the same.”
   He completely got it. I didn’t need to say or do anything else.
   Now, when I eat an apple, it tastes a little sweeter than before. What perfect fruit it is!