R₁=20 Ω
R₂=40 Ω
R₃=60 Ω
I₃=2 A
P₁ = ?
[tex]R_{12}=R_1+R_2=20+40=60 \ \Omega\\ \\U_{12}=U_3=U\\ \\I_3=\frac{U}{R_3} \ \ \rightarrow U=I_3*R_3=2 \ [A]*60 \ [\Omega]=120 \ V[/tex]
[tex]R_{12}=R_3 \ \ \rightarrow \ \ I_{12}=I_3[/tex]
[tex]U_1=I_{12}*R_1=2 \ [A]*20 \ [\Omega]=40 \ V\\ \\P_1=U_1*I_{12}=40 \ [V]*2 \ [A]=80 \ W[/tex]
lub
[tex]P_1=U_1*I_{12} \ \ \ U_1=I_{12}*R_1 \ \ \rightarrow \ \ P_1=(I_{12}*R_1)*I_{12}=I_{12}^2*R_1=2^2*20=4*20=80 \ W[/tex]
