在如图所示的电路中，灯泡L正常发光．当滑动变阻器的滑片P向左滑动的过程中，下列说法正确的是（ ）
A．灯泡的实际功率变大
B．灯泡的实际功率变小
C．电流表示数变大
D．电压表示数变大
（1）由电路图可知，当滑动变阻器的滑片P向左滑动时，滑动变阻器接入电路的阻值变大，
滑动变阻器分压变大，电压表示数变大，故D正确；
（2）滑动变阻器接入电路阻值变大，电路总电阻变大，电源电压不变，由欧姆定律可知，
电路电流变小，电流表示数变小，故C错误；
（3）电源电压不变，滑动变阻器分压变大，灯泡两端电压U变小，电路电流I变小，
灯泡实际功率P=UI变小，故A错误，B正确；
故选BD．
“Sending thank-you notes is becoming a lost art,” mourns May Mitchell, a syndicated columnist known as “Ms Demeanor” and author of six etiquette(礼节) books. In her view, each generation, compared with the one before, is losing a sense of consideration for other people. “Without respect,” she says, “you have conflict.” Ms. Demeanor would be proud of me: I have figured out a way to ensure that my children always send thank-you notes. And such a gesture is important, says Ms. Demeanor, because “a grateful attitude is a tremendous life skill, an efficient and inexpensive way to set ourselves apart in the work force and in our adult lives. Teach your children that the habit of manners comes from inside---it’s an attitude based on respecting other people.” A few years ago, as my children descended like piranhas (一种南美淡水鱼，喜吞食或攻击) on their presents under the Christmas tree, the only attitude I could see was greed. Where was the appreciation of time and effort? A thank-you note should contain three things: an acknowledgement of the gift (Love the tie with the picture of a hose on it); a recognition of the time and effort spent to select it (You must have shopped all over the state find such a unique item!); a prediction of how you will use your gift or the way it has enhanced your life (I’ll be sure to wear it to the next Mr. Ed convention!). So, five years ago, in one of my rare flashes of parental insight, I decided that the most appropriate time to teach this basic courtesy is while the tinsel (装饰用光亮金属) is hot. To the horror of my children, I announced that henceforth every gift received will be an occasion for a thank-you note written immediately, on the spot. I have reluctantly given my kids the green light to send e-mail thank-you notes; though hand-lettered ones (at least to me) still seem friendlier. But pretty much any thank-you makes the gift giver feel special—just as, we hope, the recipient feels. It’s a gesture that perfectly captures the spirit of the holidays. 41. 小题1:in Ms. Demeanor’s point of view, children born in the ______ is probably the least respectful generation.
|