Bài 19:
\(MCD:R_1nt\left(R_2//R_3\right)\)
\(R_{23}=\dfrac{R_2.R_3}{R_2+R_3}=\dfrac{15.10}{15+10}=6\left(\Omega\right)\)
\(R_{tđ}=R_1+R_{23}=9+6=15\left(\Omega\right)\)
Do mắc nối tiếp nên \(I=I_1=I_{23}=0,5\left(A\right)\)
\(U_{23}=U_2=U_3=I_{23}.R_{23}=0,5.6=3\left(V\right)\)
\(\left\{{}\begin{matrix}I_2=\dfrac{U_2}{R_2}=\dfrac{3}{15}=0,2\left(A\right)\\I_3=\dfrac{U_3}{R_3}=\dfrac{3}{10}=0,3\left(A\right)\end{matrix}\right.\)
\(U_1=I_1.R_1=0,5.9=4,5\left(V\right)\)
Bài 20:
\(MCD:R_1//\left(R_2ntR_3\right)\)
\(R_{23}=R_2+R_3=20+10=30\left(\Omega\right)\)
\(R_{tđ}=\dfrac{R_1.R_{23}}{R_1+R_{23}}=\dfrac{20.30}{20+30}=12\left(\Omega\right)\)
Do mắc song song nên: \(U=U_1=U_{23}=30V\)
\(I_1=\dfrac{U_1}{R_1}=\dfrac{30}{20}=1,5\left(A\right)\)
\(I=\dfrac{U}{R_{tđ}}=\dfrac{30}{12}=2,5\left(A\right)\)
\(I_{23}=I_2=I_3=\dfrac{U_{23}}{R_{23}}=\dfrac{30}{30}=1\left(A\right)\)
\(\left\{{}\begin{matrix}U_2=I_2.R_2=1.20=20\left(V\right)\\U_3=I_3.R_3=1.10=10\left(V\right)\end{matrix}\right.\)
