Question

如图所示，电源电压恒定不变，小灯泡L上标有“6V•3W”字样，滑动变阻器R最大阻值36Ω，灯泡电阻不随温度变化．闭合S、S1、S2，当滑动变阻器滑片位于最右端时，电压表示数为3V；闭合S、S1，断开S2，当滑动变阻器滑片位于最左端时，灯泡正常发光. 求：

             

⑴电源电压；                                                                                                                  

                                                                                                                                

⑵R0的阻值．                                                                                                                 

                                                                                                                                

                                                                                                    

                                                                                                                                

                                                                                                                                

Answer 1

⑴灯L的额定电流I额=P额/U额=3W/6V=0.5A，R灯=U额/I额=12Ω。当闭合开关S1、S2、S3时，且滑片在最右端时，电路中R和L串联。电压表测L两端电压。                                                                                                       

I=U/R=3V/12Ω=0.25A                                                                                                                       

UR=IR=0.25A×36Ω=9V则电源电压U总=9V+3V=12V                                                                                                 

⑵当滑片在最左端时，电路中L和R0串联。此时L正常工作说明分到6V的电压。                                                                                                     

UR0=U总—UR=12V-6V=6V，此时的I等于灯泡L的额定电流0.5A，                                                                                                          

则R0=U0/I=6V/0.5A=12Ω