题目

用标有“6V 3W”的灯L1和“6V 6W”的灯L2及“18Ω 2A”的滑动变阻器等元件设计了如图所示电路。当闭合开关S、S1、S2，滑动变阻器的滑片移至最右端时，两灯都正常发光（灯丝电阻不变），此时电流表示数为_____A；在电流表有示数的前提下，该电路最小功率为_____W。 答案：【答案】1.5 1.2 【解析】[1]当闭合开关S、S1、S2，滑动变阻器的滑片移至最右端时，两灯并联且都正常发光，电流表测干路中的电流，根据可得，灯L1中的电流灯L2中的电流因为两灯并联，所以电路中的总电流即电流表的示数为1.5A。[2]当变阻器R的阻值最大，且和两灯中电阻较大的灯泡串联时，电路中的总20、Mr. Smith left his car outside his house one night as usual．But when he came out the next morning，he found his car wasn’t there．He called the police to tell them about it，and they said they would try to find it．     When Mr. Smith came home from his office that evening，the car was back again in its usual place in front of his house．He looked it over carefully and found it OK．But there were two tickets on one of the seats with a letter．It said，“We’re sorry we used your car for a day．Thank you very much．The tickets are for you．We hope you’ll enjoy yourselves．”     The Smiths went to the cinema with the tickets at night．When they got home，they found nearly everything in the house was gone． 根据短文内容，判断正（T）、误（F）。 （   ）1．Mr. Smith came out the next morning but he couldn’t find his ear． （   ）2．Someone used his car for three days． （   ）3．The Smiths called the police but they would not like to help them． （   ）4．The two tickets on the seat showed real sorry to the Smiths． （   ）5．The thief gave Mr. Smith two tickets and took away almost everything．