b) Cường độ dòng điện qua \[{{\rm{R}}_{\rm{3}}}\]là 1A

Sai

Từ mạch điện ta thấy

\[{{\rm{R}}_{\rm{1}}}\,{\rm{nt }}\left( {{{\rm{R}}_{\rm{2}}}\,{\rm{//}}\,{{\rm{R}}_{\rm{3}}}} \right)\, \Rightarrow \left\{ \begin{array}{l}I\,{\rm{ = }}\,{{\rm{I}}_{\rm{1}}}\,{\rm{ = }}\,{{\rm{I}}_{{\rm{23}}}}\,{\rm{ = }}\,{\rm{4 A}}\\{{\rm{U}}_{{\rm{23}}}}\,{\rm{ = }}\,{{\rm{U}}_{\rm{2}}}\,{\rm{ = }}\,{{\rm{U}}_{\rm{3}}}\\{{\rm{I}}_{{\rm{23}}}}\,{\rm{ = }}\,{{\rm{I}}_{\rm{2}}}\,{\rm{ + }}\,{{\rm{I}}_{\rm{3}}}\end{array} \right.\, \Rightarrow \,\left\{ \begin{array}{l}{I_2}\, + \,{I_3}\, = 4A\\{I_2}{R_2}\, = \,{I_3}{R_3}\end{array} \right.\, \Leftrightarrow \left\{ \begin{array}{l}{I_2}\, + \,{I_3}\, = 4A\\3{I_2} = \,{I_3}\end{array} \right.\,\left\{ \begin{array}{l}{I_2}\, = 1\,A\\{I_3}\, = \,3\,A\end{array} \right.\]