把两个电阻并联接入电路,R'=2R",干路的电流为2.7A若将它们串联接入同一电路,电流是多少?

并联时,1/R1=1/R'+1/R'',1/R1=1/2R''+1/R'',R1=2R''/3
U=I1R1=2.7×(2R''/3)=1.8R''
串联时,U=1.8R'',R2=R'+R''=3R'',I2=U/R2=1.8R''/3R''=0.6(A)
答：略.