+) Mắc nối tiếp:
\(R_{tđ}=R_1+R_2=30+10=40\left(\Omega\right)\)
\(I=I_1=I_2=\dfrac{U}{R_{tđ}}=\dfrac{12}{40}=0,3\left(A\right)\)
\(\left\{{}\begin{matrix}U_1=I_1.R_1=0,3.30=9\left(V\right)\\U_2=I_2.R_2=0,3.10=3\left(V\right)\end{matrix}\right.\)
+) Mắc song song:
\(U=U_1=U_2=12V\)