$1.$ $-$ Tóm tắt: $\\$$R_1 = 15\ \Omega$ $\\$ $R_2 = 4\ \Omega$, $R_3 = 6\ \Omega$ $\\$ $R_4 = 8\ \Omega$ $\\$ $I = 2,5 A$ $\\$ $------------$ $\\$ Sơ đồ mạch điện: $\\$ $[R_1 // (R_2$ $ nối$ $tiếp$ $R_3)]$ $nối$ $tiếp $ $R_4$. $\\$ $⇒ R_{23} = R_2 + R_3 = 4 + 6 = 10$ $(\Omega)$ $\\$ $⇒ R_{123} = \dfrac{R_1 . R_{23}}{R_1 + R_{23}} = \dfrac{15 . 10}{15 + 10} = 6$ $(\Omega)$ $\\$ $⇒ R_{AB} = R_{123} + R_4 = 6 + 8 = 14$ $(\Omega)$ $(đpcm)$ $\\$ $R_4$ mắc $nt$ với mạch chính $⇒ I_4 = I = 2,5$ $(A)$. $\\$ $U_{123} = I .R_{123} = 2,5 . 6 = 15$ $(V)$. $\\$ $I_1 = \dfrac{U_{123}}{R_1} = \dfrac{15}{15} = 1$ $(A)$. $\\$ $I_2 = I_3 = \dfrac{U_{123}}{R_{23}} = \dfrac{15}{10} = 1,5$ $(A)$. $\\$ $------------------------------$ $\\$ $2.$ $-$ Tóm tắt: $\\$ $R_1 = 3\ \Omega, R_2 = 6\ \Omega$ $\\$ $R_3 = 10\ \Omega, R_4 = 15\ \Omega$ $\\$ $U_{AB} = 16V$ $\\$ $------------$ $\\$ $-$ Sơ đồ mạch điện: $\\$ $(R_1 // R_2)$ $nối$ $tiếp$ $(R_3 // R_4)$. $\\$ $R_{12} = \dfrac{R_1 .R_2}{R_1 + R_2} = \dfrac{3 . 6}{3 + 6} = 2$ $\Omega$$\\$ $R_{34} = \dfrac{R_3 . R_4}{R_3 + R_4} = \dfrac{10 .15}{10 + 15} = 6$ $\Omega$.$\\$ $R_{AB} = R_{12} + R_{34} = 2 + 6 = 8$ $\Omega$. $(đpcm)$ $\\$ $I = \dfrac{U_{AB}}{R_{AB}} = \dfrac{16}{8} = 2A$. $\\$ $U_{12} = I . R_{12} = 2 . 2 = 4V$. $\\$ $U_{34} = I . R_{34} = 2 . 6 = 12V$. $\\$ $I_1 = \dfrac{U_{12}}{R_1} = \dfrac{4}{3} ≈ 1,33A$. $\\$ $I_2 = \dfrac{U_{12}}{R_2} = \dfrac{4}{6} ≈ 0,67A$. $\\$ $I_3 = \dfrac{U_{34}}{R_3} = \dfrac{12}{10} = 1,2A$. $\\$ $I_4 = \dfrac{U_{34}}{R_4} = \dfrac{12}{15} = 0,8A$. $\\$ $------------------------------$ $\\$ $\color{red}{MINH} \color{yellow}{NGUYEN} \color{red}{5751}$