Question

Giúp mik vs

Answer 1

\(MCD:R_1//R_2\)

\(\Rightarrow R_{td}=\dfrac{R_1\cdot R_2}{R_1+R_2}=\dfrac{18\cdot12}{18+12}=7,2\Omega\)

Ta có: \(U=U_1=U_2=18V\Rightarrow\left\{{}\begin{matrix}I=\dfrac{U}{R}=\dfrac{18}{7,2}=2,5A\\I_1=\dfrac{U_1}{R_1}=\dfrac{18}{18}=1A\\I_2=\dfrac{U_2}{R_2}=\dfrac{18}{12}=1,5A\end{matrix}\right.\)

\(\Rightarrow\left\{{}\begin{matrix}Q=UIt=18\cdot2,5\cdot30\cdot60=81000J\\Q_1=U_1I_1t=18\cdot1\cdot30\cdot60=32400J\\Q_2=U_2I_2t=18\cdot1,5\cdot30\cdot60=48600J\end{matrix}\right.\)

Ta có: \(P'=2P=2UI=2\cdot18\cdot1,5=54\)W

\(P'=UI'\Rightarrow I'=\dfrac{P'}{U}=\dfrac{54}{18}=3A\)

\(\Rightarrow R_3=\dfrac{U_3}{I_3}=\dfrac{18}{3-1,5}=12\Omega\)