Bài 1:
a) \(R_{tđ}=R_1+R_2=5+15=20\left(\Omega\right)\)
b) \(I=I_1=I_2=0,2\left(A\right)\)
\(\left\{{}\begin{matrix}U_1=I_1.R_1=0,2.5=1\left(V\right)\\U_2=I_2.R_2=0,2.15=3\left(V\right)\\U_m=U_1+U_2=1+3=4\left(V\right)\end{matrix}\right.\)
c) \(P_1=U_1.I_1=1.0,2=0,2\left(W\right)\)
\(Q_{tỏa}=A=P.t=U.I.t=4.0,2.30.60=1440\left(J\right)\)
Bài 2:
a) \(R_{tđ}=\dfrac{U}{I}=\dfrac{9}{0,3}=30\left(\Omega\right)\)
\(R_{tđ}=R_1+R_2\Rightarrow R_2=R_{tđ}-R_1=30-5=25\left(\Omega\right)\)
b) \(P=U.I=9.0,3=2,7\left(W\right)\)
c) \(I=I_1=I_2=0,3\left(A\right)\)
\(Q_{tỏa_1}=A_1=P_1.t=I_1^2.R.t=0,3^2.5.10.60=270\left(J\right)\)
Bài 3:
a) \(R_{tđ}=R_1+R_2=12+36=48\left(\Omega\right)\)
\(I=I_1=I_2=\dfrac{U}{R_{tđ}}=\dfrac{12}{48}=0,25\left(A\right)\)
b) \(R_1=\rho_1\dfrac{l_1}{S_1}\Rightarrow l_1=\dfrac{R_1.S_1}{\rho_1}=\dfrac{12.0,4.10^{-6}}{0,4.10^{-6}}=12\left(m\right)\)
c) \(P_2=I_2^2.R_2=0,25^2.36=2,25\left(W\right)\)
\(Q_{tỏa}=A=P.t=U.I.t=0,25.12.20.60=3600\left(J\right)=1.10^{-3}\left(kWh\right)\)
