a) vì R1 nt R2 nên [tex]R_{td}=R_1+R_2=5+8=13\Omega[/tex]
b) vì R1 nt R2 nên [tex]I_C=I_1=I_2=\frac{U}{R_{td}}=\frac{7}{13}(V)[/tex]
c) [tex]\left\{\begin{matrix} P_1=I_1^2.R_1=(\frac{7}{13})^2.5 & & \\ P_2=I_1^2.R_2=(\frac{7}{13})^2.8 & & \end{matrix}\right.[/tex]
d) [tex]A=U.I.T=7.\frac{7}{13}.(30.4.60.60)[/tex]
e) [tex]I_{dm_{D}}=\frac{P}{U}=\frac{1}{2} R_{D}=\frac{U_D^2}{P_D}=10(\Omega )\Rightarrow I'=T_D=I_2=\frac{U}{R_{td}'}=\frac{U}{R_D+R_2}=\frac{7}{10+8}=\frac{7}{18}\Rightarrow I_D < I_{dm_{D}} \Rightarrow [/tex] đèn sáng yếu