如图1所示，电源电压保持不变，小灯泡的额定电压为12V．闭合开关S后，当滑片P从最右端滑到最左端的过程中，小灯泡的I-U关系图象如图2所示．则小灯泡的额定功率为______W，电源电压为______V，滑动变阻器的最大阻值为______Ω．
①由图象知，在灯泡两端电压为U额=12V时，通过的电流为I额=2A
所以灯泡的额定功率为P额=U额I额=12V×2A=24W；
②当滑片位于最左端时，滑动变阻器阻值为0，此时灯泡两端电压等于电源电压
所以电源电压为U=U额=12V；
③当滑片在最右端时，滑动变阻器全部接入电路，由图象知，此时灯泡两端电压为UL=3V，电路电流为I=1A
所以滑动变阻器两端电压为UR=U-UL=12V-3V=9V
滑动变阻器的最大阻值为R=
=UR I
=9Ω．9V 1A
故答案为：24；12；9．
. 第四部分: 任务型填空( 共10小题,满分10分) Teaching kids to fish sometimes puzzles us parents. Now I’d like to give you a few tips. First of all, start them young. Get them in a boat, or on a pier(码头), or on the bank at as young an age as you possibly can. Obviously this means being extremely conscious about their safety. Whatever you do, DON’T plan on any fishing yourself. If fishing is going to happen, the fishing will be done by the kids with your help! This lets you pay attention to them and not ignore them while you fish. Next, make sure you plan the first trips to someplace where you can actually catch a lot of fish. At this point, it doesn’t matter what kind or how big, just make sure they can catch some. A small child’s patience is very short, and waiting 30 minutes for a bite will turn them off in a hurry. You may need to go to a small pond where the fish are dying to eat bread balls. Any type of fish will do. Remember, this is for them, not for you. As they fish, cheer for every fish they catch. Make a really big deal out of it. Take pictures. And if it’s possible, take some home to clean. Let the child help you clean with a table knife, so he can’t get hurt. Make sure he makes and sees the connection from catching to cleaning to cooking. As soon as you have the fish cleaned, it’s into the kitchen to start cooking. Make him flour and cornmeal the fish. Let him see the fish cooking, and talk about how good they are. Then when it’s ready, make sure you brag（吹嘘） on the fact that he (or she ) caught these fish, and “aren’t they good?” In this way, I’m sure your kids will be interested in fishing and good at fishing. Title: Teach a kid to fish
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