R1和R2串联,P1:P2=R1:R2=2:1
I=3I'=3*根号下W2:R2t=3*根号下120J:8Ω*60s=1.5A开关S1、S2闭合时,R1和R3并联如电路;I3=IR1:R3=1.5A*4Ω:8Ω=0.75A
干路电流:I''=I+I3=1.5A+0.75A=2.25A
R1和R2串联,P1:P2=R1:R2=2:1
I=3I'=3*根号下W2:R2t=3*根号下120J:8Ω*60s=1.5A开关S1、S2闭合时,R1和R3并联如电路;I3=IR1:R3=1.5A*4Ω:8Ω=0.75A
干路电流:I''=I+I3=1.5A+0.75A=2.25A