串联电路中,R总=R1+R2串联电路电流处处相等,I=I1=I2总电压等于各电压之和,U=U1+U2R总=U/I=(U1+U2)/I=U1/I+U2/I=U1/I1+U2/I2=R1+R2
并联电路中,R总=R1R2/(R1+R2)并联电路中,各支路电压相等,U=U1=U2干路电流等于各支路电压之和,I=I1+I2R总=U/I=U/(I1+I2)1/R总=(I1+I2)/U=I1/U+I2/U=I1/U1+I2/U2=1/R1+1/R21/R总=(R1+R2)/(R1R2)R总=R1R2/(R1+R2)