R=R1+R2怎么推导

问题描述:

R=R1+R2怎么推导
(串联电路)

串联电路:U1+U2=U,
I1=I2=I,
R1=U1/I1=U1/I
R2=U2/I2=U2/I
R=U/I
U1/I+U2/I=(U1+U2)/I=U/I=R
所以R=R1+R2