Câu 14:
\(\dfrac{1}{R_{tđ}}=\dfrac{1}{R_1}+\dfrac{1}{R_2}+\dfrac{1}{R_3}=\dfrac{1}{2}+\dfrac{1}{3}+\dfrac{1}{6}=1\Rightarrow R_{tđ}=1\left(\Omega\right)\)
\(I=\dfrac{U}{R_{tđ}}=\dfrac{6}{1}=6\left(A\right)\left(B\right)\)
Câu 15:
\(R_1=\rho\dfrac{l_1}{S_1},R_2=\rho\dfrac{l_2}{S_2}\)
\(\Rightarrow\dfrac{R_1}{R_2}=\dfrac{\dfrac{l_1}{S_1}}{\dfrac{l_2}{S_2}}=\dfrac{l_1}{S_1}:\dfrac{3l_1}{\dfrac{1}{2}S_1}=\dfrac{\dfrac{1}{2}}{3}=\dfrac{1}{6}\Rightarrow R_2=6R_1\left(A\right)\)
Bài 17:
\(R_{tđ}=R_1+R_2=2+10=12\left(\Omega\right)\)
\(I=I_1=I_2=\dfrac{U_1}{R_1}=\dfrac{5}{2}\left(A\right)\)
\(U=I.R_{tđ}=\dfrac{5}{2}.12=30\left(V\right)\)
