Question

如圖所示，電源電壓恒定不變，小燈泡L上標(biāo)有“6V•3W”字樣，滑動變阻器R最大阻值36Ω，燈泡電阻不隨溫度變化．閉合S、S1、S2，當(dāng)滑動變阻器滑片位于最右端時，電壓表示數(shù)為3V；閉合S、S1，斷開S2，當(dāng)滑動變阻器滑片位于最左端時，燈泡正常發(fā)光. 求：

             

⑴電源電壓；                                                                                                                  

                                                                                                                                

⑵R0的阻值．                                                                                                                 

                                                                                                                                

                                                                                                    

                                                                                                                                

                                                                                                                                

Answer 1

⑴燈L的額定電流I額=P額/U額=3W/6V=0.5A，R燈=U額/I額=12Ω。當(dāng)閉合開關(guān)S1、S2、S3時，且滑片在最右端時，電路中R和L串聯(lián)。電壓表測L兩端電壓。                                                                                                       

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

UR=IR=0.25A×36Ω=9V則電源電壓U總=9V+3V=12V                                                                                                 

⑵當(dāng)滑片在最左端時，電路中L和R0串聯(lián)。此時L正常工作說明分到6V的電壓。                                                                                                     

UR0=U總—UR=12V-6V=6V，此時的I等于燈泡L的額定電流0.5A，                                                                                                          

則R0=U0/I=6V/0.5A=12Ω